Dépouillements

A method for three-dimensional Navier–Stokes simulations of large-scale regions of the human lung airway / D. Keith Walters in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : A method for three-dimensional Navier–Stokes simulations of large-scale regions of the human lung airway Type de document : texte imprimé Auteurs : D. Keith Walters, Auteur ; William H. Luke, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  computational  fluid  dynamics;  engineering  simulation;  bifurcation;  boundary-value  problems;  geometry;  lung;  tree  (data  structure) Résumé : A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented. The new approach provides a means for detailed resolution of the flow features via three-dimensional Navier–Stokes CFD simulation without the need for full resolution of the entire flow geometry, which is well beyond the reach of available computing power now and in the foreseeable future. The method is based on a finite number of flow paths, each of which is fully resolved, to provide a detailed description of the entire complex small-scale flowfield. A stochastic coupling approach is used for the unresolved flow path boundary conditions, yielding a virtual flow geometry that allows accurate statistical resolution of the flow at all scales for any set of flow conditions. Results are presented for multigenerational lung models based on the Weibel morphology and the anatomical data of and (1992, “Physical Models of the Smaller Pulmonary Airways,” J. Appl. Physiol., 72(6), pp. 2402–2414). Validation simulations are performed for a portion of the bronchiole region (generations 4–12) using the flow path ensemble method, and compared with simulations that are geometrically fully resolved. Results are obtained for three inspiratory flowrates and compared in terms of pressure drop, flow distribution characteristics, and flow structure. Results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by up to an order of magnitude. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] A method for three-dimensional Navier–Stokes simulations of large-scale regions of the human lung airway [texte imprimé] / D. Keith Walters, Auteur ; William H. Luke, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : pressure;  flow  (dynamics);  computational  fluid  dynamics;  engineering  simulation;  bifurcation;  boundary-value  problems;  geometry;  lung;  tree  (data  structure) Résumé : A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented. The new approach provides a means for detailed resolution of the flow features via three-dimensional Navier–Stokes CFD simulation without the need for full resolution of the entire flow geometry, which is well beyond the reach of available computing power now and in the foreseeable future. The method is based on a finite number of flow paths, each of which is fully resolved, to provide a detailed description of the entire complex small-scale flowfield. A stochastic coupling approach is used for the unresolved flow path boundary conditions, yielding a virtual flow geometry that allows accurate statistical resolution of the flow at all scales for any set of flow conditions. Results are presented for multigenerational lung models based on the Weibel morphology and the anatomical data of and (1992, “Physical Models of the Smaller Pulmonary Airways,” J. Appl. Physiol., 72(6), pp. 2402–2414). Validation simulations are performed for a portion of the bronchiole region (generations 4–12) using the flow path ensemble method, and compared with simulations that are geometrically fully resolved. Results are obtained for three inspiratory flowrates and compared in terms of pressure drop, flow distribution characteristics, and flow structure. Results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by up to an order of magnitude. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Analysis and prevention of vortex breakdown in the simplified discharge cone of a Francis turbine / Romeo Susan-Resiga in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 15 p. Titre : Analysis and prevention of vortex breakdown in the simplified discharge cone of a Francis turbine Type de document : texte imprimé Auteurs : Romeo Susan-Resiga, Auteur ; Sebastian Muntean, Auteur ; Hasmatuchi, Vlad, Auteur Année de publication : 2010 Article en page(s) : 15 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  turbulence;  kinetic  energy;  stress;  diffusers;  turbines;  vortices;  electrical  discharge;  swirling  flow;  Francis  turbines Résumé : We perform a numerical analysis of the decelerated swirling flow into the discharge cone of a model Francis turbine operated at variable discharge and constant head, using an axisymmetric turbulent swirling flow model and a corresponding simplified computational domain. Inlet boundary conditions correspond to velocity and turbulent kinetic energy profiles measured downstream the Francis runner. Our numerical results are validated against experimental data on a survey section further downstream in the cone, showing that the Reynolds stress turbulence model with a quadratic pressure-strain term correctly captures the flow field. It is shown that the diffuser performance quickly deteriorates as the turbine discharge decreases, due to the occurrence and development of vortex breakdown, with a central quasistagnant region. We investigate a novel flow control technique, which uses a water jet injected from the runner crown tip along the axis. It is shown that the jet discharge can be optimized for minimum overall losses, while the vortex breakdown is eliminated. This flow control method is useful for mitigating the Francis turbine flow instabilities when operating at partial discharge. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Analysis and prevention of vortex breakdown in the simplified discharge cone of a Francis turbine [texte imprimé] / Romeo Susan-Resiga, Auteur ; Sebastian Muntean, Auteur ; Hasmatuchi, Vlad, Auteur . - 2010 . - 15 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 15 p. Mots-clés : pressure;  flow  (dynamics);  turbulence;  kinetic  energy;  stress;  diffusers;  turbines;  vortices;  electrical  discharge;  swirling  flow;  Francis  turbines Résumé : We perform a numerical analysis of the decelerated swirling flow into the discharge cone of a model Francis turbine operated at variable discharge and constant head, using an axisymmetric turbulent swirling flow model and a corresponding simplified computational domain. Inlet boundary conditions correspond to velocity and turbulent kinetic energy profiles measured downstream the Francis runner. Our numerical results are validated against experimental data on a survey section further downstream in the cone, showing that the Reynolds stress turbulence model with a quadratic pressure-strain term correctly captures the flow field. It is shown that the diffuser performance quickly deteriorates as the turbine discharge decreases, due to the occurrence and development of vortex breakdown, with a central quasistagnant region. We investigate a novel flow control technique, which uses a water jet injected from the runner crown tip along the axis. It is shown that the jet discharge can be optimized for minimum overall losses, while the vortex breakdown is eliminated. This flow control method is useful for mitigating the Francis turbine flow instabilities when operating at partial discharge. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

LES of the slipstream of a rotating train / Hassan Hemida in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Titre : LES of the slipstream of a rotating train Type de document : texte imprimé Auteurs : Hassan Hemida, Auteur ; Nahia Gil, Auteur ; Chris Baker, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  boundary  layers;  trains;  slipstream Résumé : The slipstream of a high-speed train was investigated using large-eddy simulation (LES). The subgrid stresses were modeled using the standard Smagorinsky model. The train model consisted of a four-coach of a 1/25 scale of the ICE2 train. The model was attached to a 3.61 m diameter rotating rig. The LES was made at two Reynolds numbers of 77,000 and 94,000 based on the height of the train and its speed. Three different computational meshes were used in the simulations: course, medium and fine. The coarse, medium, and fine meshes consisted of 6×106, 10×106, and 15×106 nodes, respectively. The results of the fine mesh are in fairly agreement with the experimental data. Different flow regions were obtained using the LES: upstream region, nose region, boundary layer region, intercarriage gap region, tail region, and wake region. Localized velocity peak was obtained near the nose of the train. The maximum and minimum pressure values are also noticed near to the nose tip. Coherent structures were born at the nose and roof of the train. These structures were swept by the radial component of the velocity toward the outer side of the train. These structures extended for a long distance behind the train in the far wake flow. The intercarriage gaps and the underbody complexities, in the form of supporting cylinders, were shown to have large influences on the slipstream velocity. The results showed that the slipstream velocity is linearly proportional to the speed of the train in the range of our moderate Reynolds numbers. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] LES of the slipstream of a rotating train [texte imprimé] / Hassan Hemida, Auteur ; Nahia Gil, Auteur ; Chris Baker, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Mots-clés : pressure;  flow  (dynamics);  boundary  layers;  trains;  slipstream Résumé : The slipstream of a high-speed train was investigated using large-eddy simulation (LES). The subgrid stresses were modeled using the standard Smagorinsky model. The train model consisted of a four-coach of a 1/25 scale of the ICE2 train. The model was attached to a 3.61 m diameter rotating rig. The LES was made at two Reynolds numbers of 77,000 and 94,000 based on the height of the train and its speed. Three different computational meshes were used in the simulations: course, medium and fine. The coarse, medium, and fine meshes consisted of 6×106, 10×106, and 15×106 nodes, respectively. The results of the fine mesh are in fairly agreement with the experimental data. Different flow regions were obtained using the LES: upstream region, nose region, boundary layer region, intercarriage gap region, tail region, and wake region. Localized velocity peak was obtained near the nose of the train. The maximum and minimum pressure values are also noticed near to the nose tip. Coherent structures were born at the nose and roof of the train. These structures were swept by the radial component of the velocity toward the outer side of the train. These structures extended for a long distance behind the train in the far wake flow. The intercarriage gaps and the underbody complexities, in the form of supporting cylinders, were shown to have large influences on the slipstream velocity. The results showed that the slipstream velocity is linearly proportional to the speed of the train in the range of our moderate Reynolds numbers. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Influence of the slant angle of 3D bluff bodies on longitudinal vortex formation / Patrick Gilliéron in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Titre : Influence of the slant angle of 3D bluff bodies on longitudinal vortex formation Type de document : texte imprimé Auteurs : Patrick Gilliéron, Auteur ; Annie Leroy, Auteur ; Sandrine Aubrun, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  vortices;  pressure  gradient;  swirling  flow Résumé : This paper presents the experimental results and analytical arguments concerning simplified geometries of the rear window and windscreen of automotive vehicles in order to contribute to a better understanding of the swirling structure formation and vortex bursting processes. Static pressure distributions and skin friction line visualizations on both sides of the edge where the swirling structure is generated on the rear window of an Ahmed body are presented for different slant angles. Results show the influence of the slant angle on the swirling structure formation and further show that the vortex bursting process can be promoted by small rear window angles. These results are then extrapolated with the help of analytical demonstrations to the windscreen configuration to demonstrate that large windscreen slopes would have the same disintegration effect. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Influence of the slant angle of 3D bluff bodies on longitudinal vortex formation [texte imprimé] / Patrick Gilliéron, Auteur ; Annie Leroy, Auteur ; Sandrine Aubrun, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Mots-clés : pressure;  flow  (dynamics);  vortices;  pressure  gradient;  swirling  flow Résumé : This paper presents the experimental results and analytical arguments concerning simplified geometries of the rear window and windscreen of automotive vehicles in order to contribute to a better understanding of the swirling structure formation and vortex bursting processes. Static pressure distributions and skin friction line visualizations on both sides of the edge where the swirling structure is generated on the rear window of an Ahmed body are presented for different slant angles. Results show the influence of the slant angle on the swirling structure formation and further show that the vortex bursting process can be promoted by small rear window angles. These results are then extrapolated with the help of analytical demonstrations to the windscreen configuration to demonstrate that large windscreen slopes would have the same disintegration effect. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Particle trajectory study in submerged flows with baffles using ν2¯−f and k−ε turbulence models / A. Mehdizadeh in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 10 p. Titre : Particle trajectory study in submerged flows with baffles using ν2¯−f and k−ε turbulence models Type de document : texte imprimé Auteurs : A. Mehdizadeh, Auteur ; B. Firoozabadi, Auteur ; S. A. Sherif, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  particulate  matter;  turbulence;  trajectories  (physics);  erosion;  equations Résumé : In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (ν2¯−f model) has been used to simulate this submerged flow. In recent years, the ν2¯−f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the ν2¯−f model is superior to other Reynolds-averaged Navier-Stokes (RANS) methods in many flows where complex flow features are present. In this study, we compare the results of the ν2¯−f model with available experimental data. Since erosion and deposition are coupled, the study of this problem should consider both of these phenomena using a proper approach. In addition to erosion over the bed, the trajectory of the particles is examined using a Lagrangian–Eulerian approach, the distribution of deposited particles over the bed is predicted for a two-phase test case based on a series of numerical simulations. Results show that the maximum erosion happens in a place in which no particle can be deposited, which causes the bed to deform very rapidly in that region. This should help prevent or reduce erosion over the bed. On the other hand, the study will help predict the trajectory of particles and the deposition rates at any section of the channel, and should thus provide useful information to control the erosion and deposition on the channel bed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Particle trajectory study in submerged flows with baffles using ν2¯−f and k−ε turbulence models [texte imprimé] / A. Mehdizadeh, Auteur ; B. Firoozabadi, Auteur ; S. A. Sherif, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 10 p. Mots-clés : flow  (dynamics);  particulate  matter;  turbulence;  trajectories  (physics);  erosion;  equations Résumé : In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (ν2¯−f model) has been used to simulate this submerged flow. In recent years, the ν2¯−f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the ν2¯−f model is superior to other Reynolds-averaged Navier-Stokes (RANS) methods in many flows where complex flow features are present. In this study, we compare the results of the ν2¯−f model with available experimental data. Since erosion and deposition are coupled, the study of this problem should consider both of these phenomena using a proper approach. In addition to erosion over the bed, the trajectory of the particles is examined using a Lagrangian–Eulerian approach, the distribution of deposited particles over the bed is predicted for a two-phase test case based on a series of numerical simulations. Results show that the maximum erosion happens in a place in which no particle can be deposited, which causes the bed to deform very rapidly in that region. This should help prevent or reduce erosion over the bed. On the other hand, the study will help predict the trajectory of particles and the deposition rates at any section of the channel, and should thus provide useful information to control the erosion and deposition on the channel bed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Investigation of the flow field in a rectangular vessel equipped with a side-entering agitator / C. Gómez in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 13 p. Titre : Investigation of the flow field in a rectangular vessel equipped with a side-entering agitator Type de document : texte imprimé Auteurs : C. Gómez, Auteur ; C. P. J. Bennington, Auteur ; F. Taghipour, Auteur Année de publication : 2010 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  lasers;  measurement;  particulate  matter;  impellers;  computational  fluid  dynamics;  blades;  errors;  vessels Résumé : The hydrodynamics of stirred vessels with side-entering impellers, which are used in numerous process industries including petroleum, foods, and pulp and paper manufacturing, have received limited attention. In the present work, the flow in a reduced size rectangular tank equipped with a side-entering axial flow impeller, scaled down from the industrial agitation of low consistency pulp fiber suspensions, was investigated using particle image velocimetry (PIV) and computational fluid dynamics (CFD), in the laminar regime (18≤Re≤120). Tuning of the PIV measuring parameters for an optimum capture of valid velocity vectors within a representative portion of the vessel is described. A detailed description of the construction and refinement of the grid and quantification of the discretization error in the CFD results is also presented. The simulation predictions were extensively evaluated by comparing the measured planar flow patterns and velocity fields at various locations in the mixing vessel. Very good agreement was found between PIV measurements and computed velocities confirming the efficiency of CFD in the analysis of mixing systems. The prediction of global mixing parameters was also evaluated. The computed impeller torque and impeller power number agreed very well with experimental measurements over the range of Re studied. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Investigation of the flow field in a rectangular vessel equipped with a side-entering agitator [texte imprimé] / C. Gómez, Auteur ; C. P. J. Bennington, Auteur ; F. Taghipour, Auteur . - 2010 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 13 p. Mots-clés : flow  (dynamics);  lasers;  measurement;  particulate  matter;  impellers;  computational  fluid  dynamics;  blades;  errors;  vessels Résumé : The hydrodynamics of stirred vessels with side-entering impellers, which are used in numerous process industries including petroleum, foods, and pulp and paper manufacturing, have received limited attention. In the present work, the flow in a reduced size rectangular tank equipped with a side-entering axial flow impeller, scaled down from the industrial agitation of low consistency pulp fiber suspensions, was investigated using particle image velocimetry (PIV) and computational fluid dynamics (CFD), in the laminar regime (18≤Re≤120). Tuning of the PIV measuring parameters for an optimum capture of valid velocity vectors within a representative portion of the vessel is described. A detailed description of the construction and refinement of the grid and quantification of the discretization error in the CFD results is also presented. The simulation predictions were extensively evaluated by comparing the measured planar flow patterns and velocity fields at various locations in the mixing vessel. Very good agreement was found between PIV measurements and computed velocities confirming the efficiency of CFD in the analysis of mixing systems. The prediction of global mixing parameters was also evaluated. The computed impeller torque and impeller power number agreed very well with experimental measurements over the range of Re studied. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

A study of cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow in an IC engine / Mayank Mittal in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : A study of cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow in an IC engine Type de document : texte imprimé Auteurs : Mayank Mittal, Auteur ; Harold J. Schock, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  measurement;  fuels;  turbulence;  engines;  kinetic  energy;  motion  control;  computer-aided  design;  internal  combustion  engines;  valves;  compression;  cycles;  cylinders;  engine  cylinders;  flow  measurement Résumé : An experimental study is performed to investigate the cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow measurement inside an internal combustion engine assembly. Molecular tagging velocimetry (MTV) is used to obtain the multiple point measurement of the instantaneous velocity field. MTV is a molecular counterpart of particle-based techniques, and it eliminates the use of seed particles. A two-component velocity field is obtained at various crank angle degrees for tumble and swirl measurement planes inside an optical engine assembly (1500 rpm and 2500 rpm engine speeds). Effects of charge motion control are studied considering different cases of: (i) charge motion control valve (CMCV) deactivated and (ii) CMCV activated. Both the measurement planes are used in each case to study the cycle-to-cycle variability inside an engine cylinder. Probability density functions of the normalized circulation are calculated from the instantaneous planar velocity to quantify the cycle-to-cycle variations of in-cylinder flows. In addition, the turbulent kinetic energy of flow is calculated and compared with the results of the probability density function. Different geometries of CMCV produce different effects on the in-cylinder flow field. It is found that the charge motion control used in this study has a profound effect on cycle-to-cycle variations during the intake and early compression; however, its influence reduces during the late compression. Therefore, it can be assumed that CMCV enhances the fuel-air mixing more than the flame speed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] A study of cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow in an IC engine [texte imprimé] / Mayank Mittal, Auteur ; Harold J. Schock, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : flow  (dynamics);  measurement;  fuels;  turbulence;  engines;  kinetic  energy;  motion  control;  computer-aided  design;  internal  combustion  engines;  valves;  compression;  cycles;  cylinders;  engine  cylinders;  flow  measurement Résumé : An experimental study is performed to investigate the cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow measurement inside an internal combustion engine assembly. Molecular tagging velocimetry (MTV) is used to obtain the multiple point measurement of the instantaneous velocity field. MTV is a molecular counterpart of particle-based techniques, and it eliminates the use of seed particles. A two-component velocity field is obtained at various crank angle degrees for tumble and swirl measurement planes inside an optical engine assembly (1500 rpm and 2500 rpm engine speeds). Effects of charge motion control are studied considering different cases of: (i) charge motion control valve (CMCV) deactivated and (ii) CMCV activated. Both the measurement planes are used in each case to study the cycle-to-cycle variability inside an engine cylinder. Probability density functions of the normalized circulation are calculated from the instantaneous planar velocity to quantify the cycle-to-cycle variations of in-cylinder flows. In addition, the turbulent kinetic energy of flow is calculated and compared with the results of the probability density function. Different geometries of CMCV produce different effects on the in-cylinder flow field. It is found that the charge motion control used in this study has a profound effect on cycle-to-cycle variations during the intake and early compression; however, its influence reduces during the late compression. Therefore, it can be assumed that CMCV enhances the fuel-air mixing more than the flame speed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Fluid force moment on the backshroud of a Francis turbine runner in precession motion / Bingwei Song in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : Fluid force moment on the backshroud of a Francis turbine runner in precession motion Type de document : texte imprimé Auteurs : Bingwei Song, Auteur ; Hironori Horiguchi, Auteur ; Yumeto Nishiyama, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  pressure;  rotation;  flow  (dynamics);  fluids;  motion;  clearances  (engineering);  disks;  computation;  leakage  flows;  Francis  turbines Résumé : The fundamental characteristics of rotordynamic fluid force moment on the backshroud of a Francis turbine runner in precession motion were studied using model tests and computations based on a bulk flow model. The runner is modeled by a disk positioned close to a casing with a small axial clearance. An inward leakage flow is produced by an external pump in the model test. The effects of the leakage flow rate, the preswirl velocity at the inlet of the clearance, and the axial clearance on the fluid force moment were examined. It was found that the fluid force moment encourages the precession motion at small forward precession angular velocity ratios and the region encouraging the precession motion is affected by the preswirl velocity. Through the comparisons of the fluid force moment with and without the rotation of the disk, it was found that the normal moment without the disk rotation did not have the effect to encourage the precession motion. Thus, the swirl flow due to disk rotation was found to be responsible for the encouragement of the precession motion. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Fluid force moment on the backshroud of a Francis turbine runner in precession motion [texte imprimé] / Bingwei Song, Auteur ; Hironori Horiguchi, Auteur ; Yumeto Nishiyama, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : force;  pressure;  rotation;  flow  (dynamics);  fluids;  motion;  clearances  (engineering);  disks;  computation;  leakage  flows;  Francis  turbines Résumé : The fundamental characteristics of rotordynamic fluid force moment on the backshroud of a Francis turbine runner in precession motion were studied using model tests and computations based on a bulk flow model. The runner is modeled by a disk positioned close to a casing with a small axial clearance. An inward leakage flow is produced by an external pump in the model test. The effects of the leakage flow rate, the preswirl velocity at the inlet of the clearance, and the axial clearance on the fluid force moment were examined. It was found that the fluid force moment encourages the precession motion at small forward precession angular velocity ratios and the region encouraging the precession motion is affected by the preswirl velocity. Through the comparisons of the fluid force moment with and without the rotation of the disk, it was found that the normal moment without the disk rotation did not have the effect to encourage the precession motion. Thus, the swirl flow due to disk rotation was found to be responsible for the encouragement of the precession motion. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Axial flow fan tip leakage flow control using tip platform extensions / Ali Aktürk in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 10 p. Titre : Axial flow fan tip leakage flow control using tip platform extensions Type de document : texte imprimé Auteurs : Ali Aktürk, Auteur ; Cengiz Camci, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  measurement;  clearances  (engineering);  rotors;  axial  flow;  blades;  leakage  flows;  leakage Résumé : Performance of an axial flow fan unit is closely related to its tip leakage mass flow rate and level of tip/casing interactions. The present experimental study uses a stereoscopic particle image velocimeter to quantify the three dimensional mean flow observed near the blade tip, just downstream of a ducted fan unit. After a comprehensive description of the exit flow from the baseline fan, a number of novel tip treatments based on custom designed pressure side extensions are introduced. Various tip leakage mitigation schemes are introduced by varying the chordwise location and the width of the extension in the circumferential direction. The current study shows a proper selection of the pressure side bump location and width are the two critical parameters influencing the success of each tip leakage mitigation approach. Significant gains in the axial mean velocity component are observed when a proper pressure side tip extension is used. It is also observed that a proper tip leakage mitigation scheme significantly reduces the tangential velocity component near the tip of the axial fan blade. Reduced tip clearance related flow interactions are essential in improving the energy efficiency of ducted fan systems. A reduction or elimination of the momentum deficit in tip vortices is also essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Axial flow fan tip leakage flow control using tip platform extensions [texte imprimé] / Ali Aktürk, Auteur ; Cengiz Camci, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 10 p. Mots-clés : pressure;  flow  (dynamics);  measurement;  clearances  (engineering);  rotors;  axial  flow;  blades;  leakage  flows;  leakage Résumé : Performance of an axial flow fan unit is closely related to its tip leakage mass flow rate and level of tip/casing interactions. The present experimental study uses a stereoscopic particle image velocimeter to quantify the three dimensional mean flow observed near the blade tip, just downstream of a ducted fan unit. After a comprehensive description of the exit flow from the baseline fan, a number of novel tip treatments based on custom designed pressure side extensions are introduced. Various tip leakage mitigation schemes are introduced by varying the chordwise location and the width of the extension in the circumferential direction. The current study shows a proper selection of the pressure side bump location and width are the two critical parameters influencing the success of each tip leakage mitigation approach. Significant gains in the axial mean velocity component are observed when a proper pressure side tip extension is used. It is also observed that a proper tip leakage mitigation scheme significantly reduces the tangential velocity component near the tip of the axial fan blade. Reduced tip clearance related flow interactions are essential in improving the energy efficiency of ducted fan systems. A reduction or elimination of the momentum deficit in tip vortices is also essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Prediction of the nonuniform tip clearance effect on the axial compressor flow field / Young-Seok Kang in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Titre : Prediction of the nonuniform tip clearance effect on the axial compressor flow field Type de document : texte imprimé Auteurs : Young-Seok Kang, Auteur ; Shin-Hyoung Kang, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  pressure;  flow  (dynamics);  compressors;  clearances  (engineering);  design;  modeling;  rotors;  blades;  equations Résumé : It is well-known that nonuniform tip clearance in an axial compressor induces pressure and velocity perturbations along the circumferential direction. This study develops a numerical modeling to predict perturbed flows in an axial compressor with a nonuniform tip clearance and presents a mechanism of the flow redistribution in the axial compressor at design and off-design conditions. The modeling results are compared with CFD results (2006, “Prediction of the Fluid Induced Instability Force of an Axial Compressor,” ASME FEDSM 2006 , Miami, FL) not only to validate the present modeling, but also to investigate more detailed flow fields. In an axial compressor, nonuniform tip clearance varies local flow passage area and resultant axial velocity along the circumferential direction. There are small axial velocity differences between maximum and minimum clearances near the design condition, while large pressure differences are investigated according to local locations. However, contribution of the main flow region overrides the tip clearance effect as the flow coefficient deviates from the design condition. Moreover, the flow field redistribution becomes noticeably strong when the off-design effects are incorporated. In case of high flow coefficients, the low relative flow angle near the minimum clearance regions results in a large negative incidence angle and forms a large flow recirculation region and a corresponding large amount of loss occurs near the blade pressure surface. It further promotes strong flow field perturbations at the off-design conditions. The integration of these pressure and blade loading perturbations with a control volume analysis leads to the well-known Alford’s force. Alford’s force is always negative near the design condition; however, it reverses its sign to positive at the high flow coefficients. At the high flow coefficients, tip leakage flow effects lessen, while increased off-design effects amplify blade loading perturbations and a steep increase in Alford’s force. This study enables that nonuniform flow field, and the resultant Alford’s force, which may result in an unstable rotor-dynamic behavior, can be easily evaluated and assessed during the compressor, fan, or blower design process. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Prediction of the nonuniform tip clearance effect on the axial compressor flow field [texte imprimé] / Young-Seok Kang, Auteur ; Shin-Hyoung Kang, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Mots-clés : force;  pressure;  flow  (dynamics);  compressors;  clearances  (engineering);  design;  modeling;  rotors;  blades;  equations Résumé : It is well-known that nonuniform tip clearance in an axial compressor induces pressure and velocity perturbations along the circumferential direction. This study develops a numerical modeling to predict perturbed flows in an axial compressor with a nonuniform tip clearance and presents a mechanism of the flow redistribution in the axial compressor at design and off-design conditions. The modeling results are compared with CFD results (2006, “Prediction of the Fluid Induced Instability Force of an Axial Compressor,” ASME FEDSM 2006 , Miami, FL) not only to validate the present modeling, but also to investigate more detailed flow fields. In an axial compressor, nonuniform tip clearance varies local flow passage area and resultant axial velocity along the circumferential direction. There are small axial velocity differences between maximum and minimum clearances near the design condition, while large pressure differences are investigated according to local locations. However, contribution of the main flow region overrides the tip clearance effect as the flow coefficient deviates from the design condition. Moreover, the flow field redistribution becomes noticeably strong when the off-design effects are incorporated. In case of high flow coefficients, the low relative flow angle near the minimum clearance regions results in a large negative incidence angle and forms a large flow recirculation region and a corresponding large amount of loss occurs near the blade pressure surface. It further promotes strong flow field perturbations at the off-design conditions. The integration of these pressure and blade loading perturbations with a control volume analysis leads to the well-known Alford’s force. Alford’s force is always negative near the design condition; however, it reverses its sign to positive at the high flow coefficients. At the high flow coefficients, tip leakage flow effects lessen, while increased off-design effects amplify blade loading perturbations and a steep increase in Alford’s force. This study enables that nonuniform flow field, and the resultant Alford’s force, which may result in an unstable rotor-dynamic behavior, can be easily evaluated and assessed during the compressor, fan, or blower design process. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Flow and dipole source evaluation of a generic SUV / Jonas Ask in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 12 p. Titre : Flow and dipole source evaluation of a generic SUV Type de document : texte imprimé Auteurs : Jonas Ask, Auteur ; Lars Davidson, Auteur Année de publication : 2010 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  measurement;  acoustics;  dipoles  (electromagnetism);  resolution  (optics);  noise  (sound);  engineering  simulation;  vehicles;  geometry;  mirrors Résumé : Accurately predicting both average flow quantities and acoustic sources at the front window of today’s ground vehicles are still a considerable challenge to automotive companies worldwide. One of the most important aspects in terms of obtaining not only trustworthy results but also the most tedious one and therefore perhaps overlooked, is the control and outcome of the mesh generation process. Generating unstructured volume meshes suitable for large eddy simulations with high level representation of geometrical details is both a time consuming and an extremely computer demanding activity. This work investigates two different mesh generation processes with its main aim to evaluate their outcome with respect to the prediction of the two dominating dipole sources in a temporal form of the Curle’s equation. Only a handful of papers exists that report a high level representation of the vehicle geometry and the aim of predicting the fluctuating exterior noise sources. To the author’s knowledge no studies have been conducted in which both these source terms are evaluated quantitatively against measurements. The current paper investigates the degree to which the amplitude of these two source terms can be predicted by using the traditional law-of-the-wall and hex-dominant meshes with isotropic resolution boxes for a detailed ground vehicle geometry. For this purpose, the unstructured segregated commercial FLUENT finite volume method code is used. The flow field is treated as incompressible and the Smagorinsky–Lilly model is used to compute the subgrid stresses. Mean flow quantities are measured with a 14 hole probe for 14 rakes downstream of the side mirror. The dynamic pressure sensors are distributed at 16 different positions over the side window to capture the fluctuating pressure signals. All measurements in this work were conducted at Ford’s acoustic wind tunnel in Cologne. All three simulations accurately predict the velocity magnitude closest to the window and downstream of the mirror head recirculation zone. Some variations in the size and shape of this recirculation zone are found between the different meshes, most probably caused by differences in the detachment of the mirror head boundary layer. The Strouhal number of the shortest simulation was computed from the fundamental frequency of the drag force coefficient. The computed Strouhal number agrees well with the corresponding results from similar objects and gives an indication of an acceptable simulation time. The dynamic pressure sensors at 16 different locations at the vehicle side window were also used to capture the levels of the two dipole source terms. These results are compared with the three simulations. With the exception of three positions, at least one of the three simulations accurately captures the levels of both source terms up to about 1000 Hz. The three positions with less agreement as compared with measurements were found to be in regions sensitive to small changes in the local flow direction. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Flow and dipole source evaluation of a generic SUV [texte imprimé] / Jonas Ask, Auteur ; Lars Davidson, Auteur . - 2010 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 12 p. Mots-clés : pressure;  flow  (dynamics);  measurement;  acoustics;  dipoles  (electromagnetism);  resolution  (optics);  noise  (sound);  engineering  simulation;  vehicles;  geometry;  mirrors Résumé : Accurately predicting both average flow quantities and acoustic sources at the front window of today’s ground vehicles are still a considerable challenge to automotive companies worldwide. One of the most important aspects in terms of obtaining not only trustworthy results but also the most tedious one and therefore perhaps overlooked, is the control and outcome of the mesh generation process. Generating unstructured volume meshes suitable for large eddy simulations with high level representation of geometrical details is both a time consuming and an extremely computer demanding activity. This work investigates two different mesh generation processes with its main aim to evaluate their outcome with respect to the prediction of the two dominating dipole sources in a temporal form of the Curle’s equation. Only a handful of papers exists that report a high level representation of the vehicle geometry and the aim of predicting the fluctuating exterior noise sources. To the author’s knowledge no studies have been conducted in which both these source terms are evaluated quantitatively against measurements. The current paper investigates the degree to which the amplitude of these two source terms can be predicted by using the traditional law-of-the-wall and hex-dominant meshes with isotropic resolution boxes for a detailed ground vehicle geometry. For this purpose, the unstructured segregated commercial FLUENT finite volume method code is used. The flow field is treated as incompressible and the Smagorinsky–Lilly model is used to compute the subgrid stresses. Mean flow quantities are measured with a 14 hole probe for 14 rakes downstream of the side mirror. The dynamic pressure sensors are distributed at 16 different positions over the side window to capture the fluctuating pressure signals. All measurements in this work were conducted at Ford’s acoustic wind tunnel in Cologne. All three simulations accurately predict the velocity magnitude closest to the window and downstream of the mirror head recirculation zone. Some variations in the size and shape of this recirculation zone are found between the different meshes, most probably caused by differences in the detachment of the mirror head boundary layer. The Strouhal number of the shortest simulation was computed from the fundamental frequency of the drag force coefficient. The computed Strouhal number agrees well with the corresponding results from similar objects and gives an indication of an acceptable simulation time. The dynamic pressure sensors at 16 different locations at the vehicle side window were also used to capture the levels of the two dipole source terms. These results are compared with the three simulations. With the exception of three positions, at least one of the three simulations accurately captures the levels of both source terms up to about 1000 Hz. The three positions with less agreement as compared with measurements were found to be in regions sensitive to small changes in the local flow direction. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Flows and their stability in rotating cylinders with a porous lining / M. Subotic in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Titre : Flows and their stability in rotating cylinders with a porous lining Type de document : texte imprimé Auteurs : M. Subotic, Auteur ; F. C. Lai, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : stability;  flow  (dynamics);  fluids;  linings  (textiles);  cylinders;  thickness Résumé : Flow fields in an annulus between two rotating cylinders with a porous lining have been numerically examined in this study. While the outer cylinder is stationary, the inner cylinder is rotating with a constant angular speed. A homogeneous and isotropic porous layer is press-fit to the inner surface of the outer cylinder. The porous sleeve is saturated with the fluid that fills the annulus. The effects of porous sleeve thickness and its properties on the flows and their stability in the annulus are numerically investigated. Three-dimensional momentum equations for the porous and fluid layers are formulated separately and solved simultaneously in terms of velocity and vorticity. The solutions have covered a wide range of the governing parameters (10−5≤Da≤10−2, 2000≤Ta≤5000, 0.8≤b¯≤0.95). The results obtained show that the presence of a porous sleeve generally has a stabilizing effect on the flows in the annulus. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Flows and their stability in rotating cylinders with a porous lining [texte imprimé] / M. Subotic, Auteur ; F. C. Lai, Auteur . - 2010 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Mots-clés : stability;  flow  (dynamics);  fluids;  linings  (textiles);  cylinders;  thickness Résumé : Flow fields in an annulus between two rotating cylinders with a porous lining have been numerically examined in this study. While the outer cylinder is stationary, the inner cylinder is rotating with a constant angular speed. A homogeneous and isotropic porous layer is press-fit to the inner surface of the outer cylinder. The porous sleeve is saturated with the fluid that fills the annulus. The effects of porous sleeve thickness and its properties on the flows and their stability in the annulus are numerically investigated. Three-dimensional momentum equations for the porous and fluid layers are formulated separately and solved simultaneously in terms of velocity and vorticity. The solutions have covered a wide range of the governing parameters (10−5≤Da≤10−2, 2000≤Ta≤5000, 0.8≤b¯≤0.95). The results obtained show that the presence of a porous sleeve generally has a stabilizing effect on the flows in the annulus. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Active control of flow separation in a radial blower / Greenblatt, David in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 06 p. Titre : Active control of flow separation in a radial blower Type de document : texte imprimé Auteurs : Greenblatt, David, Auteur ; Guy Arzuan, Auteur Année de publication : 2010 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  separation  (technology);  acoustics;  Reynolds  number;  impellers;  flow  visualization;  shear  (mechanics);  actuators;  blades;  flat  plates;  flow  separation;  frequency;  airfoils Résumé : An experimental investigation was undertaken as a proof-of-concept study for active separation control in a radial blower. Acoustic perturbations were introduced into the impeller housing of a small radial blower with fully stalled blades. Increases in the plenum pressure of 35% were achieved and, based on tuft-based flow visualization, it was concluded that the pressure increases were brought about due to excitation and deflection of the leading-edge separated shear layer. Within the parameter range considered here, the optimum dimensionless control frequencies were found to be O(0.5), irrespective of the blade orientation or number of blades. Moreover, the maximum pressure rise was achieved with an investment of only 2% of the fan input power. Backward bladed impeller blades exhibited slightly larger increases in pressure coefficients when compared with their forward bladed counterparts. The dependence of blower performance on reduced frequency was remarkably similar to that seen on flat plate airfoils at similar Reynolds numbers under periodic excitation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Active control of flow separation in a radial blower [texte imprimé] / Greenblatt, David, Auteur ; Guy Arzuan, Auteur . - 2010 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 06 p. Mots-clés : pressure;  separation  (technology);  acoustics;  Reynolds  number;  impellers;  flow  visualization;  shear  (mechanics);  actuators;  blades;  flat  plates;  flow  separation;  frequency;  airfoils Résumé : An experimental investigation was undertaken as a proof-of-concept study for active separation control in a radial blower. Acoustic perturbations were introduced into the impeller housing of a small radial blower with fully stalled blades. Increases in the plenum pressure of 35% were achieved and, based on tuft-based flow visualization, it was concluded that the pressure increases were brought about due to excitation and deflection of the leading-edge separated shear layer. Within the parameter range considered here, the optimum dimensionless control frequencies were found to be O(0.5), irrespective of the blade orientation or number of blades. Moreover, the maximum pressure rise was achieved with an investment of only 2% of the fan input power. Backward bladed impeller blades exhibited slightly larger increases in pressure coefficients when compared with their forward bladed counterparts. The dependence of blower performance on reduced frequency was remarkably similar to that seen on flat plate airfoils at similar Reynolds numbers under periodic excitation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Spectral linear stochastic estimation of the turbulent velocity in a square three-dimensional wall jet / Joseph W. Hall in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Titre : Spectral linear stochastic estimation of the turbulent velocity in a square three-dimensional wall jet Type de document : texte imprimé Auteurs : Joseph W. Hall, Auteur ; Daniel Ewing, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  fluids;  channels  (hydraulic  engineering);  turbulence;  fluctuations  (physics) Résumé : The instantaneous turbulent velocity field in a three-dimensional wall jet was estimated from the fluctuating wall pressure using a spectral linear stochastic estimation technique. The wall jet investigated issued from a long square channel with Reynolds number of 90,000. Two downstream positions in the intermediate field were examined, x/h=10 and x/h=20, owing to the rapid changes in wall jet development over this region. The results indicate that the passage of the large-scale structures cause large, coherent lateral sweeps of fluid across the entire span of the wall jet. These sweeps are caused by the passage of half horseshoe-like structures and appear to be responsible for the larger lateral development of this flow. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Spectral linear stochastic estimation of the turbulent velocity in a square three-dimensional wall jet [texte imprimé] / Joseph W. Hall, Auteur ; Daniel Ewing, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 09 p. Mots-clés : pressure;  flow  (dynamics);  fluids;  channels  (hydraulic  engineering);  turbulence;  fluctuations  (physics) Résumé : The instantaneous turbulent velocity field in a three-dimensional wall jet was estimated from the fluctuating wall pressure using a spectral linear stochastic estimation technique. The wall jet investigated issued from a long square channel with Reynolds number of 90,000. Two downstream positions in the intermediate field were examined, x/h=10 and x/h=20, owing to the rapid changes in wall jet development over this region. The results indicate that the passage of the large-scale structures cause large, coherent lateral sweeps of fluid across the entire span of the wall jet. These sweeps are caused by the passage of half horseshoe-like structures and appear to be responsible for the larger lateral development of this flow. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Experimental study of turbulence transport in a dilute surfactant solution flow investigated by PIV / Weiguo Gu in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Titre : Experimental study of turbulence transport in a dilute surfactant solution flow investigated by PIV Type de document : texte imprimé Auteurs : Weiguo Gu, Auteur ; Yasuo Kawaguchi, Auteur ; Dezhong Wang, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  turbulence;  viscosity;  kinetic  energy;  drag  (fluid  dynamics);  Reynolds  number;  stress;  rheology;  fluctuations  (physics);  shear  (mechanics);  transportation  systems;  drag  reduction;  surfactants;  water Résumé : Drag-reducing flow of dilute surfactant solution in the two-dimensional channel is investigated experimentally by using particle image velocimetry (PIV) system. Five hundred instantaneous velocity frames of u-v in the x-y plane are taken by PIV for every condition. Fluctuation intensity and instantaneous velocity distributions are discussed in order to study the turbulence transport in the drag-reducing flow. As compared with water, the results show that wall-normal velocity fluctuations in the drag-reducing flow are suppressed significantly, and instantaneous velocity distributions display different features. Moreover, the drag-reducing flow exhibits the reduced inclination angle of turbulence transport and appearance of “zero Reynolds shear stress.” High shear dissipation also appears in some solutions. Based on the analysis of the balance of mean and mean turbulent kinetic energies, it is found that the complex rheology, i.e., the elasticity and viscosity of the solution, is considered as the main factor that change the characteristics of turbulence transport. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Experimental study of turbulence transport in a dilute surfactant solution flow investigated by PIV [texte imprimé] / Weiguo Gu, Auteur ; Yasuo Kawaguchi, Auteur ; Dezhong Wang, Auteur . - 2010 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  turbulence;  viscosity;  kinetic  energy;  drag  (fluid  dynamics);  Reynolds  number;  stress;  rheology;  fluctuations  (physics);  shear  (mechanics);  transportation  systems;  drag  reduction;  surfactants;  water Résumé : Drag-reducing flow of dilute surfactant solution in the two-dimensional channel is investigated experimentally by using particle image velocimetry (PIV) system. Five hundred instantaneous velocity frames of u-v in the x-y plane are taken by PIV for every condition. Fluctuation intensity and instantaneous velocity distributions are discussed in order to study the turbulence transport in the drag-reducing flow. As compared with water, the results show that wall-normal velocity fluctuations in the drag-reducing flow are suppressed significantly, and instantaneous velocity distributions display different features. Moreover, the drag-reducing flow exhibits the reduced inclination angle of turbulence transport and appearance of “zero Reynolds shear stress.” High shear dissipation also appears in some solutions. Based on the analysis of the balance of mean and mean turbulent kinetic energies, it is found that the complex rheology, i.e., the elasticity and viscosity of the solution, is considered as the main factor that change the characteristics of turbulence transport. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Flow characteristics of microglass fiber suspension in polymeric fluids in spherical gaps / Hiroshi Yamaguchi in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : Flow characteristics of microglass fiber suspension in polymeric fluids in spherical gaps Type de document : texte imprimé Auteurs : Hiroshi Yamaguchi, Auteur ; Xin-Rong Zhang, Auteur ; Niu, Xiao-Dong, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  fluids;  fibers;  Reynolds  number Résumé : An experimental study is carried out to investigate the effects of microglass fiber suspensions in the non-Newtonian fluids in a gap between an inner rotating sphere and an outer whole stationary sphere. In the experiments, the microglass fibers with different aspect ratios are mixed with a macromolecule polymeric fluid to obtain different suspension fluids. For comparison, a Newtonian fluid and the non-Newtonian polymeric fluid are also studied. The stationary torques of the inner sphere that the test fluids acted on are measured under conditions of various concentric spherical gaps and rotational Reynolds numbers. It is found that the polymeric fluid could be governed by the Couette flow at a gap ratio of less than 0.42 and the Reynolds number of less than 100, while the fiber-suspended polymeric fluids could expand the Couette flow region more than the Reynolds number of 100 at the same gap ratios. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Flow characteristics of microglass fiber suspension in polymeric fluids in spherical gaps [texte imprimé] / Hiroshi Yamaguchi, Auteur ; Xin-Rong Zhang, Auteur ; Niu, Xiao-Dong, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : flow  (dynamics);  fluids;  fibers;  Reynolds  number Résumé : An experimental study is carried out to investigate the effects of microglass fiber suspensions in the non-Newtonian fluids in a gap between an inner rotating sphere and an outer whole stationary sphere. In the experiments, the microglass fibers with different aspect ratios are mixed with a macromolecule polymeric fluid to obtain different suspension fluids. For comparison, a Newtonian fluid and the non-Newtonian polymeric fluid are also studied. The stationary torques of the inner sphere that the test fluids acted on are measured under conditions of various concentric spherical gaps and rotational Reynolds numbers. It is found that the polymeric fluid could be governed by the Couette flow at a gap ratio of less than 0.42 and the Reynolds number of less than 100, while the fiber-suspended polymeric fluids could expand the Couette flow region more than the Reynolds number of 100 at the same gap ratios. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Shape optimization of symmetric cylinder shape on buoyancy using Fourier series approximation / Hyeongkeun Kim in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : Shape optimization of symmetric cylinder shape on buoyancy using Fourier series approximation Type de document : texte imprimé Auteurs : Hyeongkeun Kim, Auteur ; Dongmin Choi, Auteur ; Youngjin Kim, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  buoyancy;  modeling;  optimization;  approximation;  cylinders;  Fourier  series;  rods;  shapes;  water Résumé : The hydrophobicity of water striders and fisher spiders shows the geometrical property of microsetae with elaborate nanogrooves. Studying such geometrical morphology naturally leads to the question: what is an optimal shape for buoyancy? In this paper, we present a methodology to find suboptimal shapes for star-shaped cross-sectional rods, which maximizes the buoyant force by modeling the cross-sectional shapes with Fourier series representation in the polar coordinate. We provide four suboptimal cross-sectional shapes and their experimental results. Our results support the importance of the geometrical shape for buoyant force and might be helpful in designing water repelling devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Shape optimization of symmetric cylinder shape on buoyancy using Fourier series approximation [texte imprimé] / Hyeongkeun Kim, Auteur ; Dongmin Choi, Auteur ; Youngjin Kim, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : force;  buoyancy;  modeling;  optimization;  approximation;  cylinders;  Fourier  series;  rods;  shapes;  water Résumé : The hydrophobicity of water striders and fisher spiders shows the geometrical property of microsetae with elaborate nanogrooves. Studying such geometrical morphology naturally leads to the question: what is an optimal shape for buoyancy? In this paper, we present a methodology to find suboptimal shapes for star-shaped cross-sectional rods, which maximizes the buoyant force by modeling the cross-sectional shapes with Fourier series representation in the polar coordinate. We provide four suboptimal cross-sectional shapes and their experimental results. Our results support the importance of the geometrical shape for buoyant force and might be helpful in designing water repelling devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Separation of a two-phase slug flow in branched 90 deg elbows / F. Sanchez-Silva in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Titre : Separation of a two-phase slug flow in branched 90 deg elbows Type de document : texte imprimé Auteurs : F. Sanchez-Silva, Auteur ; V. Hernandez-Perez, Auteur ; I. Carvajal-Mariscal, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  pipes;  bifurcation;  junctions;  phase  separation;  pressure  drop;  slug Résumé : Novel experimental data for phase separation of air-water mixtures in horizontal 90 deg branched elbows are presented in this work. The branched elbows were formed by attaching a pipe to a 90 deg elbow on the side of maximum radius of curvature, and halfway between the inlet and outlet sections of the elbow. All three arms coming from the junction were in the horizontal plane. Both the branch orientation and branch diameter were varied. Three different branch/elbow diameter ratios were tested, as well as three different branch inclination angles. In addition, the static pressure was monitored at different points along the ramified elbow using a set of pressure transducers in order to analyze and associate the pressure drop with the phase separation. At the inlet section of the elbow, the two-phase flow pattern was mainly slug flow. Based on the experimental data, a correlation for the liquid phase separation is proposed. Finally, the volume-weighted phase separation in the branched elbow was compared with the phase separations on the T-junction, and it was found that in some cases the branched elbows have a similar performance to that of the T-junctions. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Separation of a two-phase slug flow in branched 90 deg elbows [texte imprimé] / F. Sanchez-Silva, Auteur ; V. Hernandez-Perez, Auteur ; I. Carvajal-Mariscal, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 08 p. Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  pipes;  bifurcation;  junctions;  phase  separation;  pressure  drop;  slug Résumé : Novel experimental data for phase separation of air-water mixtures in horizontal 90 deg branched elbows are presented in this work. The branched elbows were formed by attaching a pipe to a 90 deg elbow on the side of maximum radius of curvature, and halfway between the inlet and outlet sections of the elbow. All three arms coming from the junction were in the horizontal plane. Both the branch orientation and branch diameter were varied. Three different branch/elbow diameter ratios were tested, as well as three different branch inclination angles. In addition, the static pressure was monitored at different points along the ramified elbow using a set of pressure transducers in order to analyze and associate the pressure drop with the phase separation. At the inlet section of the elbow, the two-phase flow pattern was mainly slug flow. Based on the experimental data, a correlation for the liquid phase separation is proposed. Finally, the volume-weighted phase separation in the branched elbow was compared with the phase separations on the T-junction, and it was found that in some cases the branched elbows have a similar performance to that of the T-junctions. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Microbubble drag reduction downstream of ventilated partial cavity / Eduard Amromin in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 05 p. Titre : Microbubble drag reduction downstream of ventilated partial cavity Type de document : texte imprimé Auteurs : Eduard Amromin, Auteur Année de publication : 2010 Article en page(s) : 05 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : density;  flow  (dynamics);  friction;  drag  (fluid  dynamics);  bubbles;  boundary  layers;  cavities;  computation;  drag  reduction;  flat  plates;  integral  equations;  thickness Résumé : The effect of air flux from ventilated partial cavities on drag of bodies was studied. An integral equation method for estimation of air bubble effects on drag was employed and validated with earlier known experimental data for flat plates and bodies. The qualitative difference in the effects of flow speed and air supply rate on drag of flat plates and bodies was numerically confirmed and explained as a combined effect of the boundary layer density decrease and the increase in its displacement thickness. The numerical analysis shows reduction in the total drag of ventilated bodies with increasing air flux rate up to an optimum, but the drag rise for greater rates. A synergy of friction reduction under attached ventilated cavity and microbubble drag reduction downstream of it was shown. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Microbubble drag reduction downstream of ventilated partial cavity [texte imprimé] / Eduard Amromin, Auteur . - 2010 . - 05 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 05 p. Mots-clés : density;  flow  (dynamics);  friction;  drag  (fluid  dynamics);  bubbles;  boundary  layers;  cavities;  computation;  drag  reduction;  flat  plates;  integral  equations;  thickness Résumé : The effect of air flux from ventilated partial cavities on drag of bodies was studied. An integral equation method for estimation of air bubble effects on drag was employed and validated with earlier known experimental data for flat plates and bodies. The qualitative difference in the effects of flow speed and air supply rate on drag of flat plates and bodies was numerically confirmed and explained as a combined effect of the boundary layer density decrease and the increase in its displacement thickness. The numerical analysis shows reduction in the total drag of ventilated bodies with increasing air flux rate up to an optimum, but the drag rise for greater rates. A synergy of friction reduction under attached ventilated cavity and microbubble drag reduction downstream of it was shown. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Mitigation of damage to solid surfaces from the collapse of cavitation bubble clouds / Parag V. Chitnis in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 06 p. Titre : Mitigation of damage to solid surfaces from the collapse of cavitation bubble clouds Type de document : texte imprimé Auteurs : Parag V. Chitnis, Auteur ; Nicholas J. Manzi, Auteur ; Robin O. Cleveland, Auteur Année de publication : 2010 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  ceramics;  cavitation;  bubbles;  collapse Résumé : The collapse of transient bubble clouds near a solid surface was investigated to test a scheme for mitigation of cavitation-induced damage. The target was a porous ceramic disk through which air could be forced. Transient cavitation bubbles were created using a shock-wave lithotripter focused on the surface of the disk. The dynamics of bubble clouds near the ceramic disks were studied for two boundary conditions: no back pressure resulting in surface free of bubbles and 10 psi (0.7 atm) of back pressure, resulting in a surface with a sparse (30% of area) bubble layer. Images of the cavitation near the surface were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5 MHz focused acoustic transducer) was aligned with the surface. Both the images and the acoustic measurements indicated that bubble clouds near a ceramic face without a bubble layer collapsed onto the boundary, subsequently leading to surface erosion. When a sparse bubble layer was introduced, bubble clouds collapsed away from the surface, thus mitigating cavitation damage. The erosion damage to the ceramic disks after 300 shock waves was quantified using micro-CT imaging. Pitting up to 1 mm deep was measured for the bubble-free surface, and the damage to the bubble surface was too small to be detected. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Mitigation of damage to solid surfaces from the collapse of cavitation bubble clouds [texte imprimé] / Parag V. Chitnis, Auteur ; Nicholas J. Manzi, Auteur ; Robin O. Cleveland, Auteur . - 2010 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 06 p. Mots-clés : pressure;  ceramics;  cavitation;  bubbles;  collapse Résumé : The collapse of transient bubble clouds near a solid surface was investigated to test a scheme for mitigation of cavitation-induced damage. The target was a porous ceramic disk through which air could be forced. Transient cavitation bubbles were created using a shock-wave lithotripter focused on the surface of the disk. The dynamics of bubble clouds near the ceramic disks were studied for two boundary conditions: no back pressure resulting in surface free of bubbles and 10 psi (0.7 atm) of back pressure, resulting in a surface with a sparse (30% of area) bubble layer. Images of the cavitation near the surface were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5 MHz focused acoustic transducer) was aligned with the surface. Both the images and the acoustic measurements indicated that bubble clouds near a ceramic face without a bubble layer collapsed onto the boundary, subsequently leading to surface erosion. When a sparse bubble layer was introduced, bubble clouds collapsed away from the surface, thus mitigating cavitation damage. The erosion damage to the ceramic disks after 300 shock waves was quantified using micro-CT imaging. Pitting up to 1 mm deep was measured for the bubble-free surface, and the damage to the bubble surface was too small to be detected. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Shape optimization of a multi-element foil using an evolutionary algorithm / Yu-Tai Lee in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 11 p. Titre : Shape optimization of a multi-element foil using an evolutionary algorithm Type de document : texte imprimé Auteurs : Yu-Tai Lee, Auteur ; Vineet Ahuja, Auteur ; Ashvin Hosangadi, Auteur Année de publication : 2010 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  torque;  flow  (dynamics);  computational  fluid  dynamics;  design;  engineering  simulation;  optimization;  evolutionary  algorithms;  shapes Résumé : A movable flap with a NACA foil cross section serves as a common control surface for underwater marine vehicles. To augment the functionality of the control surface, a tab assisted control (TAC) surface was experimentally tested to improve its performance especially at large angles of operation. The advantage of the TAC foil could be further enhanced with shape memory alloy (SMA) actuators to control the rear portion of the control surface to form a flexible tab (or FlexTAC) surface. Hybrid unstructured Reynolds averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) calculations were used to understand the flow physics associated with the multi-element FlexTAC foil with a stabilizer, a flap, and a flexible tab. The prediction results were also compared with the measured data obtained from both the TAC and the FlexTAC experiments. The simulations help explain subtle differences in performance of the multi-element airfoil concepts. The RANS solutions also predict the forces and moments on the surface of the hydrofoil with reasonable accuracy and the RANS procedure is found to be critical for use in a design optimization framework because of the importance of flow separation/turbulent effects in the gap region between the stabilizer and the flap. A systematic optimization study was also carried out with a genetic algorithm (GA) based design optimization procedure. This procedure searches the complex design landscape in an efficient and parallel manner. The fitness evaluations in the optimization procedure were performed with the RANS based CFD simulations. The mesh regeneration was carried out in an automated manner through a scripting process within the grid generator. The optimization calculation is performed simultaneously on both the stabilizer and the nonflexible portion of the flap. Shape changes to the trailing edge of the stabilizer strongly influence the secondary flow patterns that set up in the gap region between the stabilizer and the flap. They were found to have a profound influence on force and moment characteristics of the multi-element airfoil. A new control surface (OptimTAC) was constructed as a result of the design optimization calculation and was shown to have improved lift, drag, and torque characteristics over the original FlexTAC airfoil at high flap angles. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] Shape optimization of a multi-element foil using an evolutionary algorithm [texte imprimé] / Yu-Tai Lee, Auteur ; Vineet Ahuja, Auteur ; Ashvin Hosangadi, Auteur . - 2010 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 11 p. Mots-clés : force;  torque;  flow  (dynamics);  computational  fluid  dynamics;  design;  engineering  simulation;  optimization;  evolutionary  algorithms;  shapes Résumé : A movable flap with a NACA foil cross section serves as a common control surface for underwater marine vehicles. To augment the functionality of the control surface, a tab assisted control (TAC) surface was experimentally tested to improve its performance especially at large angles of operation. The advantage of the TAC foil could be further enhanced with shape memory alloy (SMA) actuators to control the rear portion of the control surface to form a flexible tab (or FlexTAC) surface. Hybrid unstructured Reynolds averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) calculations were used to understand the flow physics associated with the multi-element FlexTAC foil with a stabilizer, a flap, and a flexible tab. The prediction results were also compared with the measured data obtained from both the TAC and the FlexTAC experiments. The simulations help explain subtle differences in performance of the multi-element airfoil concepts. The RANS solutions also predict the forces and moments on the surface of the hydrofoil with reasonable accuracy and the RANS procedure is found to be critical for use in a design optimization framework because of the importance of flow separation/turbulent effects in the gap region between the stabilizer and the flap. A systematic optimization study was also carried out with a genetic algorithm (GA) based design optimization procedure. This procedure searches the complex design landscape in an efficient and parallel manner. The fitness evaluations in the optimization procedure were performed with the RANS based CFD simulations. The mesh regeneration was carried out in an automated manner through a scripting process within the grid generator. The optimization calculation is performed simultaneously on both the stabilizer and the nonflexible portion of the flap. Shape changes to the trailing edge of the stabilizer strongly influence the secondary flow patterns that set up in the gap region between the stabilizer and the flap. They were found to have a profound influence on force and moment characteristics of the multi-element airfoil. A new control surface (OptimTAC) was constructed as a result of the design optimization calculation and was shown to have improved lift, drag, and torque characteristics over the original FlexTAC airfoil at high flap angles. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

A serendipitous application of supercavitation theory to the water-running basilisk lizard / Eric R. White in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Titre : A serendipitous application of supercavitation theory to the water-running basilisk lizard Type de document : texte imprimé Auteurs : Eric R. White, Auteur ; Timothy F. Miller, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : dynamics  (mechanics);  simulation;  disks;  cavities;  water Résumé : The classic study of the water entry of a body has applications ranging from hydroballistics to behavior of basilisk lizards. The availability of Russian supercavitation theory in recent years has allowed for an even greater understanding, and was used to develop a model to predict the dynamic size, shape, and pressure of a naturally or artificially produced underwater cavity. This model combines supercavitation theory, rigid body dynamics, and hydrodynamic theory into a comprehensive model capable of determining the motional behavior of underwater objects. This model was used as the basis for modeling the vertical water entry of solid objects into a free water surface. Results from simulation of water entry of various-sized thin disks compared favorably with published experimental data from the technical literature. Additional simulated data support a disk radius dependence on a relative object depth at cavity closure that was not previously recognized. Cavity closure times are also presented. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] A serendipitous application of supercavitation theory to the water-running basilisk lizard [texte imprimé] / Eric R. White, Auteur ; Timothy F. Miller, Auteur . - 2010 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 07 p. Mots-clés : dynamics  (mechanics);  simulation;  disks;  cavities;  water Résumé : The classic study of the water entry of a body has applications ranging from hydroballistics to behavior of basilisk lizards. The availability of Russian supercavitation theory in recent years has allowed for an even greater understanding, and was used to develop a model to predict the dynamic size, shape, and pressure of a naturally or artificially produced underwater cavity. This model combines supercavitation theory, rigid body dynamics, and hydrodynamic theory into a comprehensive model capable of determining the motional behavior of underwater objects. This model was used as the basis for modeling the vertical water entry of solid objects into a free water surface. Results from simulation of water entry of various-sized thin disks compared favorably with published experimental data from the technical literature. Additional simulated data support a disk radius dependence on a relative object depth at cavity closure that was not previously recognized. Cavity closure times are also presented. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

On the derivation of pressure field distribution at the entrance of a rectangular capillary / Prashant R. Waghmare in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 04 p. Titre : On the derivation of pressure field distribution at the entrance of a rectangular capillary Type de document : texte imprimé Auteurs : Prashant R. Waghmare, Auteur ; Sushanta K. Mitra, Auteur Année de publication : 2010 Article en page(s) : 04 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  momentum;  flow  (dynamics);  channels  (hydraulic  engineering);  equations Résumé : In capillary flow, integral momentum approach is used to derive the governing equation, which requires an expression for the pressure field at the inlet of the capillary. Generally, the pressure field for circular capillary is deduced with hemispherical control volume. This expression has been extended for other noncircular capillaries with an equivalent radius approximation. In case of high aspect ratio channels, the semicylindrical control volume needs to be considered. In the present study, the correct expression for the entrance pressure field for high aspect ratio capillaries is derived with such appropriate control volume. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...] [article] On the derivation of pressure field distribution at the entrance of a rectangular capillary [texte imprimé] / Prashant R. Waghmare, Auteur ; Sushanta K. Mitra, Auteur . - 2010 . - 04 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 5 (Mai 2010) . - 04 p. Mots-clés : pressure;  momentum;  flow  (dynamics);  channels  (hydraulic  engineering);  equations Résumé : In capillary flow, integral momentum approach is used to derive the governing equation, which requires an expression for the pressure field at the inlet of the capillary. Generally, the pressure field for circular capillary is deduced with hemispherical control volume. This expression has been extended for other noncircular capillaries with an equivalent radius approximation. In case of high aspect ratio channels, the semicylindrical control volume needs to be considered. In the present study, the correct expression for the entrance pressure field for high aspect ratio capillaries is derived with such appropriate control volume. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27418 [...]

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse