Dépouillements

Separated flows around the rear window of a simplified car geometry / Mathieu Rouméas in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 10 p. Titre : Separated flows around the rear window of a simplified car geometry Type de document : texte imprimé Auteurs : Mathieu Rouméas, Auteur ; Patrick Gilliéron, Auteur ; Azeddine Kourta, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (dynamics);  computer  simulation;  wakes;  vortices;  geometry;  vehicles;  computation;  pressure;  vorticity;  automobiles Résumé : A 3D numerical simulation based on the lattice Boltzmann method is carried out on a simplified car geometry (initially proposed by Ahmed, Ramm, and Falting, 1984, SAE Technical Paper series No. 840300) to analyze and establish a method for controlling the near-wake flow topology of a generic blunt body model. The results indicate the existence of a complex flow topology consisting of transverse and longitudinal vortices emanating from flow separations that occur on the top and the lateral edges of the slanted rear window, respectively. The topology of each structure is detailed and the numerical results are compared with the experimental results in the literature. The results presented in this paper can then be used to develop and parametrize active control solutions conducive to improving the aerodynamic performances of automobile vehicles. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Separated flows around the rear window of a simplified car geometry [texte imprimé] / Mathieu Rouméas, Auteur ; Patrick Gilliéron, Auteur ; Azeddine Kourta, Auteur . - 2009 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 10 p. Mots-clés : Flow  (dynamics);  computer  simulation;  wakes;  vortices;  geometry;  vehicles;  computation;  pressure;  vorticity;  automobiles Résumé : A 3D numerical simulation based on the lattice Boltzmann method is carried out on a simplified car geometry (initially proposed by Ahmed, Ramm, and Falting, 1984, SAE Technical Paper series No. 840300) to analyze and establish a method for controlling the near-wake flow topology of a generic blunt body model. The results indicate the existence of a complex flow topology consisting of transverse and longitudinal vortices emanating from flow separations that occur on the top and the lateral edges of the slanted rear window, respectively. The topology of each structure is detailed and the numerical results are compared with the experimental results in the literature. The results presented in this paper can then be used to develop and parametrize active control solutions conducive to improving the aerodynamic performances of automobile vehicles. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

A differential quadrature solution of MHD natural convection in an inclined enclosure with a partition / Kamil Kahveci in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 14 p. Titre : A differential quadrature solution of MHD natural convection in an inclined enclosure with a partition Type de document : texte imprimé Auteurs : Kamil Kahveci, Auteur ; Semiha Öztuna, Auteur Année de publication : 2009 Article en page(s) : 14 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Magnetic  fields;  interior  walls;  Rayleigh  number;  flow  (dynamics);  heat  transfer;  vorticity;  natural  convection;  equations;  Prandtl  number;  fluids;  convection;  boundary  layers;  corners  (structural  elements) Résumé : Magnetohydrodynamics natural convection in an inclined enclosure with a partition is studied numerically using a differential quadrature method. Governing equations for the fluid flow and heat transfer are solved for the Rayleigh number varying from 104 to 106, the Prandtl numbers (0.1, 1, and 10), four different Hartmann numbers (0, 25, 50, and 100), the inclination angle ranging from 0degto90deg, and the magnetic field with the x and y directions. The results show that the convective flow weakens considerably with increasing magnetic field strength, and the x-directional magnetic field is more effective in reducing the convection intensity. As the inclination angle increases, multicellular flows begin to develop on both sides of the enclosure for higher values of the Hartmann number if the enclosure is under the x-directional magnetic field. The vorticity generation intensity increases with increase of Rayleigh number. On the other hand, increasing Hartmann number has a negative effect on vorticity generation. With an increase in the inclination angle, the intensity of vorticity generation is observed to shift to top left corners and bottom right corners. Vorticity generation loops in each region of enclosure form due to multicelluar flow for an x-directional magnetic field when the inclination angle is increased further. In addition, depending on the boundary layer developed, the vorticity value on the hot wall increases first sharply with increasing y and then begins to decrease gradually. For the high Rayleigh numbers, the average Nusselt number shows an increasing trend as the inclination angle increases and a peak value is detected. Beyond the peak point, the foregoing trend reverses to decrease with the further increase of the inclination angle. The results also show that the Prandtl number has only a marginal effect on the flow and heat transfer. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] A differential quadrature solution of MHD natural convection in an inclined enclosure with a partition [texte imprimé] / Kamil Kahveci, Auteur ; Semiha Öztuna, Auteur . - 2009 . - 14 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 14 p. Mots-clés : Magnetic  fields;  interior  walls;  Rayleigh  number;  flow  (dynamics);  heat  transfer;  vorticity;  natural  convection;  equations;  Prandtl  number;  fluids;  convection;  boundary  layers;  corners  (structural  elements) Résumé : Magnetohydrodynamics natural convection in an inclined enclosure with a partition is studied numerically using a differential quadrature method. Governing equations for the fluid flow and heat transfer are solved for the Rayleigh number varying from 104 to 106, the Prandtl numbers (0.1, 1, and 10), four different Hartmann numbers (0, 25, 50, and 100), the inclination angle ranging from 0degto90deg, and the magnetic field with the x and y directions. The results show that the convective flow weakens considerably with increasing magnetic field strength, and the x-directional magnetic field is more effective in reducing the convection intensity. As the inclination angle increases, multicellular flows begin to develop on both sides of the enclosure for higher values of the Hartmann number if the enclosure is under the x-directional magnetic field. The vorticity generation intensity increases with increase of Rayleigh number. On the other hand, increasing Hartmann number has a negative effect on vorticity generation. With an increase in the inclination angle, the intensity of vorticity generation is observed to shift to top left corners and bottom right corners. Vorticity generation loops in each region of enclosure form due to multicelluar flow for an x-directional magnetic field when the inclination angle is increased further. In addition, depending on the boundary layer developed, the vorticity value on the hot wall increases first sharply with increasing y and then begins to decrease gradually. For the high Rayleigh numbers, the average Nusselt number shows an increasing trend as the inclination angle increases and a peak value is detected. Beyond the peak point, the foregoing trend reverses to decrease with the further increase of the inclination angle. The results also show that the Prandtl number has only a marginal effect on the flow and heat transfer. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

The effect of free surface on the vortex shedding from inclined circular cylinders / P. P. Vlachos in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Titre : The effect of free surface on the vortex shedding from inclined circular cylinders Type de document : texte imprimé Auteurs : P. P. Vlachos, Auteur ; D. P. Telionis, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (dynamics);  measurement;  flow  visualization;  wakes;  bubbles;  vortices;  cylinders;  laser  doppler  anemometry;  vortex  shedding;  hydrogen;  visualization;  circular  cylinders;  particle  flow Résumé : Spectral analysis of laser Doppler velocimetry measurements and flow visualization are employed to study the wake of inclined cylinders piercing a free surface. The results indicate that the free surface affects vortex shedding almost two to three cylinder diameters below the free surface. Variation of the vortex axis inclination and cells of shedding were visually observed. These effects induce a phase difference in the vortex-shedding mechanism. Streamwise vortical structures are formed along the primary vortex axis. Furthermore, for the case of the highest Froude number, evidence is provided that vortex shedding is suppressed in the region near the free surface. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] The effect of free surface on the vortex shedding from inclined circular cylinders [texte imprimé] / P. P. Vlachos, Auteur ; D. P. Telionis, Auteur . - 2009 . - 9 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Mots-clés : Flow  (dynamics);  measurement;  flow  visualization;  wakes;  bubbles;  vortices;  cylinders;  laser  doppler  anemometry;  vortex  shedding;  hydrogen;  visualization;  circular  cylinders;  particle  flow Résumé : Spectral analysis of laser Doppler velocimetry measurements and flow visualization are employed to study the wake of inclined cylinders piercing a free surface. The results indicate that the free surface affects vortex shedding almost two to three cylinder diameters below the free surface. Variation of the vortex axis inclination and cells of shedding were visually observed. These effects induce a phase difference in the vortex-shedding mechanism. Streamwise vortical structures are formed along the primary vortex axis. Furthermore, for the case of the highest Froude number, evidence is provided that vortex shedding is suppressed in the region near the free surface. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Multiobjective design study of a flapping wing power generator / Eriko Shimizu in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) Titre : Multiobjective design study of a flapping wing power generator Type de document : texte imprimé Auteurs : Eriko Shimizu, Auteur ; Koji Isogai, Auteur ; Shigeru Obayashi, Auteur Année de publication : 2009 Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Design;  functions;  generators;  wings;  motion;  data  mining;  delays;  oscillations Résumé : In conventional windmills, the high tip speed creates aerodynamic noise, and when they are used at very low Reynolds numbers, their performance deteriorates due to laminar separation. These are important issues in modern windmills. Present study deals with a new windmill concept, the “flapping wing power generator,” which would solve such problems. The concept is to extract energy via the flutter phenomena and the concept has been developed by some researchers. In 2003, Isogai2003, “Design Study of Elastically Supported Flapping Wing Power Generator ,” International Forum on Aeroelasticity and Structural Dynamics, Amsterdam) proposed a new system. The system utilizes dynamic stall vortices efficiently and generates high power. The dynamic stall vortex is something that should be avoided in conventional windmills. They optimized the system to maximize the efficiency and obtained the set of design parameters, which achieved best efficiency. The system works at low frequencies and it enables high efficiency. To realize the system, it is necessary to consider the power and the efficiency. Thus, the present study optimized the system to maximize both the power and the efficiency. To obtain nondominated solutions, which are widely distributed in the design space, adaptive neighboring search, which is one of evolutionary algorithms, has been extended to handle multiple objectives and was used in the present study. Self-organizing map was used for the data mining. The trade-off between the power and the efficiency has been visualized. The trade-off curve was shaped by the constraints on the reduced frequency and the phase delay angle, which were imposed so that the dynamic stall phenomenon gives favorable effects on the power generation. The heaving amplitude was a parameter correlated to the objective functions. The reduced frequency and the phase delay angle change to control the heaving amplitude. Consequently, when the power is emphasized, the system undergoes a large heaving motion with a low frequency. On the other hand, when the efficiency is emphasized, the system undergoes a small heaving motion with a high frequency. Multiobjective optimization and data mining revealed the trade-off of the objective functions and the parameters correlated to the objective functions. The power obtained was comparable to that of present windmills at low tip-speed ratio region. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Multiobjective design study of a flapping wing power generator [texte imprimé] / Eriko Shimizu, Auteur ; Koji Isogai, Auteur ; Shigeru Obayashi, Auteur . - 2009. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) Mots-clés : Design;  functions;  generators;  wings;  motion;  data  mining;  delays;  oscillations Résumé : In conventional windmills, the high tip speed creates aerodynamic noise, and when they are used at very low Reynolds numbers, their performance deteriorates due to laminar separation. These are important issues in modern windmills. Present study deals with a new windmill concept, the “flapping wing power generator,” which would solve such problems. The concept is to extract energy via the flutter phenomena and the concept has been developed by some researchers. In 2003, Isogai2003, “Design Study of Elastically Supported Flapping Wing Power Generator ,” International Forum on Aeroelasticity and Structural Dynamics, Amsterdam) proposed a new system. The system utilizes dynamic stall vortices efficiently and generates high power. The dynamic stall vortex is something that should be avoided in conventional windmills. They optimized the system to maximize the efficiency and obtained the set of design parameters, which achieved best efficiency. The system works at low frequencies and it enables high efficiency. To realize the system, it is necessary to consider the power and the efficiency. Thus, the present study optimized the system to maximize both the power and the efficiency. To obtain nondominated solutions, which are widely distributed in the design space, adaptive neighboring search, which is one of evolutionary algorithms, has been extended to handle multiple objectives and was used in the present study. Self-organizing map was used for the data mining. The trade-off between the power and the efficiency has been visualized. The trade-off curve was shaped by the constraints on the reduced frequency and the phase delay angle, which were imposed so that the dynamic stall phenomenon gives favorable effects on the power generation. The heaving amplitude was a parameter correlated to the objective functions. The reduced frequency and the phase delay angle change to control the heaving amplitude. Consequently, when the power is emphasized, the system undergoes a large heaving motion with a low frequency. On the other hand, when the efficiency is emphasized, the system undergoes a small heaving motion with a high frequency. Multiobjective optimization and data mining revealed the trade-off of the objective functions and the parameters correlated to the objective functions. The power obtained was comparable to that of present windmills at low tip-speed ratio region. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Analysis of the cavitating draft tube vortex in a Francis turbine using particle image velocimetry measurements in two-phase flow / Monica Sanda Iliescu in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 10 p. Titre : Analysis of the cavitating draft tube vortex in a Francis turbine using particle image velocimetry measurements in two-phase flow Type de document : texte imprimé Auteurs : Monica Sanda Iliescu, Auteur ; Gabriel Dan Ciocan, Auteur ; François Avellan, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Particulate  matter;  vortices;  ropes;  Francis  turbines;  flow  (dynamics);  measurement;  cavitation Résumé : Partial flow rate operation of hydroturbines with constant pitch blades causes complex unstable cavitating flow in the diffuser cone. A particle image velocimetry (PIV) system allows investigating the flow velocity field in the case of a developing cavitation vortex, the so-called vortex rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows applying the ensemble averaging by phase technique to extract both the periodic velocity components and the rope shape. The influence of the turbine setting level on the volume of the cavity rope and its centerline is investigated, providing a physical knowledge about the hydrodynamic complex phenomena involved in the development of the cavitation rope in Francis turbine operating regimes. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Analysis of the cavitating draft tube vortex in a Francis turbine using particle image velocimetry measurements in two-phase flow [texte imprimé] / Monica Sanda Iliescu, Auteur ; Gabriel Dan Ciocan, Auteur ; François Avellan, Auteur . - 2009 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 10 p. Mots-clés : Particulate  matter;  vortices;  ropes;  Francis  turbines;  flow  (dynamics);  measurement;  cavitation Résumé : Partial flow rate operation of hydroturbines with constant pitch blades causes complex unstable cavitating flow in the diffuser cone. A particle image velocimetry (PIV) system allows investigating the flow velocity field in the case of a developing cavitation vortex, the so-called vortex rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows applying the ensemble averaging by phase technique to extract both the periodic velocity components and the rope shape. The influence of the turbine setting level on the volume of the cavity rope and its centerline is investigated, providing a physical knowledge about the hydrodynamic complex phenomena involved in the development of the cavitation rope in Francis turbine operating regimes. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Performance of two-equation turbulence models for flat plate flows with leading edge bubbles / S. Collie in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 11 p. Titre : Performance of two-equation turbulence models for flat plate flows with leading edge bubbles Type de document : texte imprimé Auteurs : S. Collie, Auteur ; M. Gerritsen, Auteur ; P. Jackson, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Shear  (mechanics);  bubbles;  boundary  layers;  flow  (dynamics);  turbulence;  flat  plates;  computational  fluid  dynamics;  kinetic  energy;  equations Résumé : This paper investigates the performance of the popular k-ω and SST turbulence models for the two-dimensional flow past the flat plate at shallow angles of incidence. Particular interest is paid to the leading edge bubble that forms as the flow separates from the sharp leading edge. This type of leading edge bubble is most commonly found in flows past thin airfoils, such as turbine blades, membrane wings, and yacht sails. Validation is carried out through a comparison to wind tunnel results compiled by Crompton (2001, “The Thin Aerofoil Leading Edge Bubble, ” Ph.D. thesis, University of Bristol). This flow problem presents a new and demanding test case for turbulence models. The models were found to capture the leading edge bubble well with the Shear-Stress Transport (SST) model predicting the reattachment length within 7% of the experimental values. Downstream of reattachment both models predicted a slower boundary layer recovery than the experimental results. Overall, despite their simplicity, these two-equation models do a surprisingly good job for this demanding test case. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Performance of two-equation turbulence models for flat plate flows with leading edge bubbles [texte imprimé] / S. Collie, Auteur ; M. Gerritsen, Auteur ; P. Jackson, Auteur . - 2009 . - 11 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 11 p. Mots-clés : Shear  (mechanics);  bubbles;  boundary  layers;  flow  (dynamics);  turbulence;  flat  plates;  computational  fluid  dynamics;  kinetic  energy;  equations Résumé : This paper investigates the performance of the popular k-ω and SST turbulence models for the two-dimensional flow past the flat plate at shallow angles of incidence. Particular interest is paid to the leading edge bubble that forms as the flow separates from the sharp leading edge. This type of leading edge bubble is most commonly found in flows past thin airfoils, such as turbine blades, membrane wings, and yacht sails. Validation is carried out through a comparison to wind tunnel results compiled by Crompton (2001, “The Thin Aerofoil Leading Edge Bubble, ” Ph.D. thesis, University of Bristol). This flow problem presents a new and demanding test case for turbulence models. The models were found to capture the leading edge bubble well with the Shear-Stress Transport (SST) model predicting the reattachment length within 7% of the experimental values. Downstream of reattachment both models predicted a slower boundary layer recovery than the experimental results. Overall, despite their simplicity, these two-equation models do a surprisingly good job for this demanding test case. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Sensitivity analysis and multiobjective optimization for LES numerical parameters / J.-C. Jouhaud in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Titre : Sensitivity analysis and multiobjective optimization for LES numerical parameters Type de document : texte imprimé Auteurs : J.-C. Jouhaud, Auteur ; P. Sagaut, Auteur ; B. Enaux, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Optimization;  errors;  functions;  response  surface  methodology;  flow  (dynamics);  sensitivity  analysis;  pareto  optimization;  viscosity;  simulation Résumé : Accuracy and reliability of large-eddy simulation data in a really complex industrial geometry are invesigated. An original methodology based on a response surface for LES data is introduced. This surrogate model for the full LES problem is built using the Kriging technique, which enables a low-cost optimal linear interpolation of a restricted set of large-eddy simulation (LES) solutions. Therefore, it can be used in most realistic industrial applications. Using this surrogate model, it is shown that (i) optimal sets of simulation parameters (subgrid model constant and artificial viscosity parameter in the present case) can be found; (ii) optimal values, as expected, depend on the cost functional to be minimized. Here, a realistic approach, which takes into account experimental data sparseness, is introduced. It is observed that minimization of the error evaluated using a too small subset of reference data may yield a global deterioration of the results. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Sensitivity analysis and multiobjective optimization for LES numerical parameters [texte imprimé] / J.-C. Jouhaud, Auteur ; P. Sagaut, Auteur ; B. Enaux, Auteur . - 2009 . - 9 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Mots-clés : Optimization;  errors;  functions;  response  surface  methodology;  flow  (dynamics);  sensitivity  analysis;  pareto  optimization;  viscosity;  simulation Résumé : Accuracy and reliability of large-eddy simulation data in a really complex industrial geometry are invesigated. An original methodology based on a response surface for LES data is introduced. This surrogate model for the full LES problem is built using the Kriging technique, which enables a low-cost optimal linear interpolation of a restricted set of large-eddy simulation (LES) solutions. Therefore, it can be used in most realistic industrial applications. Using this surrogate model, it is shown that (i) optimal sets of simulation parameters (subgrid model constant and artificial viscosity parameter in the present case) can be found; (ii) optimal values, as expected, depend on the cost functional to be minimized. Here, a realistic approach, which takes into account experimental data sparseness, is introduced. It is observed that minimization of the error evaluated using a too small subset of reference data may yield a global deterioration of the results. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Rotational motion of large particulate doublets in poiseuille flow in a capillary / E. J. McKeever in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Titre : Rotational motion of large particulate doublets in poiseuille flow in a capillary Type de document : texte imprimé Auteurs : E. J. McKeever, Auteur ; K. V. Sharp, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Rotation;  particulate  matter;  shear  (mechanics);  poiseuille  flow;  center  of  mass Résumé : Doublets of 48-μm-diameter polystyrene latex particles are experimentally tracked in a Poiseuille flow in a capillary tube. The rotational motion of nine doublets is observed using video microscopy with a translating stage. The particle diameter to capillary diameter ratio is 0.17, volume concentration 0.5%, and Reynolds number approximately 0.5. The rotational motions of the “large” particulate doublets are compared with theory originally developed for doublets with particle-to-tube diameters of the order of 0.04; the doublet rotations in the present experiments agree reasonably well with the earlier theory when the shear rate for the large doublet is defined based on the location of the centroid of shear rather than the shear rate at the radial center of mass of the rotating doublet. Additionally, these doublets are readily classified as primary or secondary on the basis of the rotational period. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Rotational motion of large particulate doublets in poiseuille flow in a capillary [texte imprimé] / E. J. McKeever, Auteur ; K. V. Sharp, Auteur . - 2009 . - 9 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 9 p. Mots-clés : Rotation;  particulate  matter;  shear  (mechanics);  poiseuille  flow;  center  of  mass Résumé : Doublets of 48-μm-diameter polystyrene latex particles are experimentally tracked in a Poiseuille flow in a capillary tube. The rotational motion of nine doublets is observed using video microscopy with a translating stage. The particle diameter to capillary diameter ratio is 0.17, volume concentration 0.5%, and Reynolds number approximately 0.5. The rotational motions of the “large” particulate doublets are compared with theory originally developed for doublets with particle-to-tube diameters of the order of 0.04; the doublet rotations in the present experiments agree reasonably well with the earlier theory when the shear rate for the large doublet is defined based on the location of the centroid of shear rather than the shear rate at the radial center of mass of the rotating doublet. Additionally, these doublets are readily classified as primary or secondary on the basis of the rotational period. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Suppression of cavitation instabilities in an inducer by J groove / Noriyuki Shimiya in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 7 p. Titre : Suppression of cavitation instabilities in an inducer by J groove Type de document : texte imprimé Auteurs : Noriyuki Shimiya, Auteur ; Akira Fujii, Auteur ; Hironori Horiguchi, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Cavitation;  blades;  leakage;  vortices;  flow  (dynamics) Résumé : The suppression of cavitation instabilities was attempted through the control of tip leakage vortex cavitation. The control was made by using shallow grooves, called J groove, on the casing wall. With J grooves, the onset regions of the rotating cavitation and the asymmetric cavitation could be diminished. However, a cavitation surge appeared at higher cavitation numbers. From the observation of cavitation, it was found that the cavitation surge occurred when the tip leakage vortex cavitation started to interact with the leading edge of the next blade. This type of cavitation surge could be avoided by extending the leading edge of the J groove upstream. However, in this case, another type of cavitation surge occurred at much lower cavitation numbers, which was caused by the cavitation between the blade surface and the tip leakage vortex cavitation. These results highlight the importance of the tip leakage vortex cavitation for cavitation instabilities. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Suppression of cavitation instabilities in an inducer by J groove [texte imprimé] / Noriyuki Shimiya, Auteur ; Akira Fujii, Auteur ; Hironori Horiguchi, Auteur . - 2009 . - 7 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 7 p. Mots-clés : Cavitation;  blades;  leakage;  vortices;  flow  (dynamics) Résumé : The suppression of cavitation instabilities was attempted through the control of tip leakage vortex cavitation. The control was made by using shallow grooves, called J groove, on the casing wall. With J grooves, the onset regions of the rotating cavitation and the asymmetric cavitation could be diminished. However, a cavitation surge appeared at higher cavitation numbers. From the observation of cavitation, it was found that the cavitation surge occurred when the tip leakage vortex cavitation started to interact with the leading edge of the next blade. This type of cavitation surge could be avoided by extending the leading edge of the J groove upstream. However, in this case, another type of cavitation surge occurred at much lower cavitation numbers, which was caused by the cavitation between the blade surface and the tip leakage vortex cavitation. These results highlight the importance of the tip leakage vortex cavitation for cavitation instabilities. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Lumped parameter analysis of an enclosed incompressible squeeze film and a central gas bubble / M. Anderson in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 8 p. Titre : Lumped parameter analysis of an enclosed incompressible squeeze film and a central gas bubble Type de document : texte imprimé Auteurs : M. Anderson, Auteur ; C. Richards, Auteur ; R. Richards, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Motion;  bubbles;  damping;  cavities;  computation;  thickness Résumé : A lumped-parameter dynamic model for an enclosed incompressible squeeze film with a central gas bubble has been derived. A new approach was applied to derive closed-form expressions for the lumped-parameter mass and damping coefficients caused by liquid motion. It was assumed that plate motions were small and the fluid behaved as a continuum. The values of the lumped-parameter mass and damping were found to depend on the aspect ratio and nondimensional squeeze-film thickness. The nondimensional thickness was given by the ratio of the actual squeeze-film thickness to the viscous penetration depth of the liquid. A nondimensional squeeze-film thickness of a value of 5 was found to divide between categories of thick and thin incompressible squeeze films. Amplification of the liquid mass and damping over and above squeeze films open to the atmosphere at the edges was found. The amplification was attributed to converging flow caused by enclosed boundaries. Comparisons between the lumped-parameter model predictions and finite-element computations showed a surprising degree of accuracy for the lumped-parameter model despite large liquid velocities in the squeeze film. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Lumped parameter analysis of an enclosed incompressible squeeze film and a central gas bubble [texte imprimé] / M. Anderson, Auteur ; C. Richards, Auteur ; R. Richards, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 8 p. Mots-clés : Motion;  bubbles;  damping;  cavities;  computation;  thickness Résumé : A lumped-parameter dynamic model for an enclosed incompressible squeeze film with a central gas bubble has been derived. A new approach was applied to derive closed-form expressions for the lumped-parameter mass and damping coefficients caused by liquid motion. It was assumed that plate motions were small and the fluid behaved as a continuum. The values of the lumped-parameter mass and damping were found to depend on the aspect ratio and nondimensional squeeze-film thickness. The nondimensional thickness was given by the ratio of the actual squeeze-film thickness to the viscous penetration depth of the liquid. A nondimensional squeeze-film thickness of a value of 5 was found to divide between categories of thick and thin incompressible squeeze films. Amplification of the liquid mass and damping over and above squeeze films open to the atmosphere at the edges was found. The amplification was attributed to converging flow caused by enclosed boundaries. Comparisons between the lumped-parameter model predictions and finite-element computations showed a surprising degree of accuracy for the lumped-parameter model despite large liquid velocities in the squeeze film. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Frequency in shedding/discharging cavitation clouds determined by visualization of a submerged cavitating jet / Ezddin A. F. Hutli in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 8 p. Titre : Frequency in shedding/discharging cavitation clouds determined by visualization of a submerged cavitating jet Type de document : texte imprimé Auteurs : Ezddin A. F. Hutli, Auteur ; Milos S. Nedeljkovic, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure;  cavitation;  nozzles;  visualization;  geometry;  sonoluminescence;  bubbles;  shapes Résumé : Visualization of a highly submerged cavitating water jet was done by high-speed camera photography in order to study and understand the jet structure and the behavior of cloud cavitation within time and space. The influencing parameters, such as injection pressure, nozzle diameter and geometry, and nozzle direction (convergent and divergent), were experimentally proven to be very significant. Periodical shedding and discharging of cavitation clouds have been also analyzed and the corresponding frequency was determined by cloud shape analysis. Additionally, the dependence of this frequency on injection pressure and nozzle geometry has been analyzed and a simple formula of correspondence has been proposed. The formula has been tested on self-measured and literature data. The recordings of sonoluminescence phenomenon proved the bubble collapse everywhere along the jet. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Frequency in shedding/discharging cavitation clouds determined by visualization of a submerged cavitating jet [texte imprimé] / Ezddin A. F. Hutli, Auteur ; Milos S. Nedeljkovic, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 8 p. Mots-clés : Pressure;  cavitation;  nozzles;  visualization;  geometry;  sonoluminescence;  bubbles;  shapes Résumé : Visualization of a highly submerged cavitating water jet was done by high-speed camera photography in order to study and understand the jet structure and the behavior of cloud cavitation within time and space. The influencing parameters, such as injection pressure, nozzle diameter and geometry, and nozzle direction (convergent and divergent), were experimentally proven to be very significant. Periodical shedding and discharging of cavitation clouds have been also analyzed and the corresponding frequency was determined by cloud shape analysis. Additionally, the dependence of this frequency on injection pressure and nozzle geometry has been analyzed and a simple formula of correspondence has been proposed. The formula has been tested on self-measured and literature data. The recordings of sonoluminescence phenomenon proved the bubble collapse everywhere along the jet. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Influence of wall inclination angles on the onset of gas entrainment during single and dual discharges from a reservoir / M. Ahmed in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 2 (Fevrier 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 16 p. Titre : Influence of wall inclination angles on the onset of gas entrainment during single and dual discharges from a reservoir Type de document : texte imprimé Auteurs : M. Ahmed, Auteur Année de publication : 2009 Article en page(s) : 16 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Bifurcation;  flow  (dynamics) Résumé : A theoretical analysis was carried out to predict the influences of wall inclination angles of large reservoirs on the onset of gas entrainment during single and dual discharges from a stratified two-phase region. The findings reveal that when the wall inclination angle differs from zero, along with low values of Froude number, two distinct flow regimes occur: the gas-entrainment and no gas-entrainment regimes. A new criterion has been developed to predict the critical Froude number at the transition from the gas-entrainment to the no-gas-entrainment regime. The critical Froude number is defined as a function of the wall inclination angle for a single discharge. For dual discharge, the critical Froude number is found to be dependent on the wall inclination angle, the separating distance between the centerlines of the two branches, as well as the Froude number of the second branch. Furthermore, four different flow regions are mapped, representing the flow regime, as well as the two-phase flow for each branch. These maps serve to predict the flow regions, mass flow rates, and quality during single and dual two-phase discharges. For the gas-entrainment regime, the predicted values of the critical height at the onset of gas entrainment are compared with the experimental data reported in literatures. Comparisons showed good concurrence between the measured and predicted results. Furthermore, the influence of the wall inclination angle on the flow regions, the predicted critical height, and the location of the gas entrainment are presented and discussed at different values of independent variables. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Influence of wall inclination angles on the onset of gas entrainment during single and dual discharges from a reservoir [texte imprimé] / M. Ahmed, Auteur . - 2009 . - 16 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 2 (Fevrier 2008) . - 16 p. Mots-clés : Bifurcation;  flow  (dynamics) Résumé : A theoretical analysis was carried out to predict the influences of wall inclination angles of large reservoirs on the onset of gas entrainment during single and dual discharges from a stratified two-phase region. The findings reveal that when the wall inclination angle differs from zero, along with low values of Froude number, two distinct flow regimes occur: the gas-entrainment and no gas-entrainment regimes. A new criterion has been developed to predict the critical Froude number at the transition from the gas-entrainment to the no-gas-entrainment regime. The critical Froude number is defined as a function of the wall inclination angle for a single discharge. For dual discharge, the critical Froude number is found to be dependent on the wall inclination angle, the separating distance between the centerlines of the two branches, as well as the Froude number of the second branch. Furthermore, four different flow regions are mapped, representing the flow regime, as well as the two-phase flow for each branch. These maps serve to predict the flow regions, mass flow rates, and quality during single and dual two-phase discharges. For the gas-entrainment regime, the predicted values of the critical height at the onset of gas entrainment are compared with the experimental data reported in literatures. Comparisons showed good concurrence between the measured and predicted results. Furthermore, the influence of the wall inclination angle on the flow regions, the predicted critical height, and the location of the gas entrainment are presented and discussed at different values of independent variables. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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