Dépouillements

Numerical simulation of emergency shutdown process of ring gate in hydraulic turbine runaway / Juliang Xiao in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Titre : Numerical simulation of emergency shutdown process of ring gate in hydraulic turbine runaway Type de document : texte imprimé Auteurs : Juliang Xiao, Auteur ; Enqiang Zhu, Auteur ; Guodong Wang, Auteur Année de publication : 2013 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  computer  simulation;  gates  (closures);  turbines;  hydraulic  turbines Résumé : A numerical model that considers the interaction between the ring gate and its neighboring components was used to simulate the emergency shutdown process of a ring gate in hydraulic turbine runaway. The three-dimensional, unsteady Navier–Stokes equations with renormalization group (RNG) k-ε turbulence models, multiphase flow models, dynamic mesh, and sliding mesh technology were applied to model the entire flow passage of the Francis hydraulic turbine, including the spiral case, stay vanes, ring gate, guide vanes, runner, and draft tube. We present a detailed analysis on the working conditions of the turbine during its runaway quitting process, the inside and outside surface pressure distributions of the ring gate, the pressure and velocity distributions of the spiral case, stay vanes, and guide vanes at different gate openings, and the loading condition of the ring gate during its closing process. The theoretical basis for improving the dynamic quality of the transient process and for hydraulic designing and optimization is provided by analyses. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Numerical simulation of emergency shutdown process of ring gate in hydraulic turbine runaway [texte imprimé] / Juliang Xiao, Auteur ; Enqiang Zhu, Auteur ; Guodong Wang, Auteur . - 2013 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Mots-clés : pressure;  flow  (dynamics);  computer  simulation;  gates  (closures);  turbines;  hydraulic  turbines Résumé : A numerical model that considers the interaction between the ring gate and its neighboring components was used to simulate the emergency shutdown process of a ring gate in hydraulic turbine runaway. The three-dimensional, unsteady Navier–Stokes equations with renormalization group (RNG) k-ε turbulence models, multiphase flow models, dynamic mesh, and sliding mesh technology were applied to model the entire flow passage of the Francis hydraulic turbine, including the spiral case, stay vanes, ring gate, guide vanes, runner, and draft tube. We present a detailed analysis on the working conditions of the turbine during its runaway quitting process, the inside and outside surface pressure distributions of the ring gate, the pressure and velocity distributions of the spiral case, stay vanes, and guide vanes at different gate openings, and the loading condition of the ring gate during its closing process. The theoretical basis for improving the dynamic quality of the transient process and for hydraulic designing and optimization is provided by analyses. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Hagen–poiseuille flow in semi-elliptic microchannels / Rajai S. Alassar in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 04 p. Titre : Hagen–poiseuille flow in semi-elliptic microchannels Type de document : texte imprimé Auteurs : Rajai S. Alassar, Auteur ; Mohammed Abushoshah, Auteur Année de publication : 2013 Article en page(s) : 04 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : friction;  channels  (hydraulic  engineering);  cross  section  (physics);  shear  (mechanics);  stress  concentration;  equations;  poiseuille  flow;  microchannels Résumé : In this paper, an exact solution of Hagen–Poiseuille flow in microchannels with semi-elliptic cross sections is obtained. The velocity, shear stress distribution, and the friction factor are calculated and compared to known approximate solutions in the literature. The solution is also verified by comparing the limiting case when the axis ratio approaches unity to the exact solution obtained for semicircular channels. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Hagen–poiseuille flow in semi-elliptic microchannels [texte imprimé] / Rajai S. Alassar, Auteur ; Mohammed Abushoshah, Auteur . - 2013 . - 04 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 04 p. Mots-clés : friction;  channels  (hydraulic  engineering);  cross  section  (physics);  shear  (mechanics);  stress  concentration;  equations;  poiseuille  flow;  microchannels Résumé : In this paper, an exact solution of Hagen–Poiseuille flow in microchannels with semi-elliptic cross sections is obtained. The velocity, shear stress distribution, and the friction factor are calculated and compared to known approximate solutions in the literature. The solution is also verified by comparing the limiting case when the axis ratio approaches unity to the exact solution obtained for semicircular channels. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Influence of blade number on the performance and pressure pulsations in a pump used as a turbine / Sun-Sheng Yang in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 10 p. Titre : Influence of blade number on the performance and pressure pulsations in a pump used as a turbine Type de document : texte imprimé Auteurs : Sun-Sheng Yang, Auteur ; Fan-Yu Kong, Auteur ; Xiao-Yun Qu, Auteur Année de publication : 2013 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  impellers;  pumps;  turbines;  blades Résumé : The rotor-stator interaction of a rotating impeller and a stationary volute could cause strong pressure pulsations and generate flow induced noise and vibration in a pump used as a turbine (PAT). Blade number is one of the main geometric parameters of the impeller. In this paper, a numerical investigation of the PAT’s unsteady pressure field with different blade numbers was performed. The accuracy of global performance prediction by computational fluid dynamics (CFD) was first verified through comparison between numerical and experimental results. Unsteady pressure fields of the PAT with different blade numbers were simulated, and the pulsations were extracted at various locations covering the PAT’s three main hydraulic parts. A detailed analysis of the unsteady pressure field distributions within the PAT’s control volume and comparison of unsteady pressure difference caused by the increase of blade number were performed. The transient flow results provided the unsteady pressure distribution within PAT and showed that increasing the blade number could effectively reduce the amplitude of pressure pulsations. Finally, unsteady pressure field tests were performed and some unsteady results obtained by unsteady field analysis were validated. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Influence of blade number on the performance and pressure pulsations in a pump used as a turbine [texte imprimé] / Sun-Sheng Yang, Auteur ; Fan-Yu Kong, Auteur ; Xiao-Yun Qu, Auteur . - 2013 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 10 p. Mots-clés : pressure;  flow  (dynamics);  impellers;  pumps;  turbines;  blades Résumé : The rotor-stator interaction of a rotating impeller and a stationary volute could cause strong pressure pulsations and generate flow induced noise and vibration in a pump used as a turbine (PAT). Blade number is one of the main geometric parameters of the impeller. In this paper, a numerical investigation of the PAT’s unsteady pressure field with different blade numbers was performed. The accuracy of global performance prediction by computational fluid dynamics (CFD) was first verified through comparison between numerical and experimental results. Unsteady pressure fields of the PAT with different blade numbers were simulated, and the pulsations were extracted at various locations covering the PAT’s three main hydraulic parts. A detailed analysis of the unsteady pressure field distributions within the PAT’s control volume and comparison of unsteady pressure difference caused by the increase of blade number were performed. The transient flow results provided the unsteady pressure distribution within PAT and showed that increasing the blade number could effectively reduce the amplitude of pressure pulsations. Finally, unsteady pressure field tests were performed and some unsteady results obtained by unsteady field analysis were validated. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

An aerodynamic investigation of an isolated rotating formula 1 wheel assembly / John Axerio-Cilies in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 16 p. Titre : An aerodynamic investigation of an isolated rotating formula 1 wheel assembly Type de document : texte imprimé Auteurs : John Axerio-Cilies, Auteur ; Gianluca Iaccarino, Auteur Année de publication : 2013 Article en page(s) : 16 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  turbulence;  manufacturing;  stress;  wakes;  computational  fluid  dynamics;  engineering  simulation;  vortices;  formulas;  geometry;  tires;  wheels;  wind  tunnels Résumé : The flowfield around a 60% scale rotating Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was examined computationally and experimentally. The goal of this study was to assess the accuracy of unsteady Reynolds-averaged Navier–Stokes (URANS) equations and confirm the existence of large scale vortical and flow recirculating features. A replica deformable F1 tire model that includes four tire treads and all brake components was used to determine the sensitivity of the wake to cross flow within the tire hub as well as the flow blockage caused by the brake assembly. Several turbulence closures were employed and the one that matched closest to the experimental PIV data was the Reynolds stress model. The variability between the six turbulence closures is shown by comparing velocity profiles, pressure distributions, and vortex eccentricity. The sensitivity of the wake to four different hub geometries, contact patch boundary conditions, multiple reference frame (MRF) rotor and spoke treatment, and time step size are also discussed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] An aerodynamic investigation of an isolated rotating formula 1 wheel assembly [texte imprimé] / John Axerio-Cilies, Auteur ; Gianluca Iaccarino, Auteur . - 2013 . - 16 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 16 p. Mots-clés : pressure;  flow  (dynamics);  turbulence;  manufacturing;  stress;  wakes;  computational  fluid  dynamics;  engineering  simulation;  vortices;  formulas;  geometry;  tires;  wheels;  wind  tunnels Résumé : The flowfield around a 60% scale rotating Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was examined computationally and experimentally. The goal of this study was to assess the accuracy of unsteady Reynolds-averaged Navier–Stokes (URANS) equations and confirm the existence of large scale vortical and flow recirculating features. A replica deformable F1 tire model that includes four tire treads and all brake components was used to determine the sensitivity of the wake to cross flow within the tire hub as well as the flow blockage caused by the brake assembly. Several turbulence closures were employed and the one that matched closest to the experimental PIV data was the Reynolds stress model. The variability between the six turbulence closures is shown by comparing velocity profiles, pressure distributions, and vortex eccentricity. The sensitivity of the wake to four different hub geometries, contact patch boundary conditions, multiple reference frame (MRF) rotor and spoke treatment, and time step size are also discussed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Dependency on runner geometry for reversible-pump turbine characteristics in turbine mode of operation / Grunde Olimstad in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Titre : Dependency on runner geometry for reversible-pump turbine characteristics in turbine mode of operation Type de document : texte imprimé Auteurs : Grunde Olimstad, Auteur ; Torbjørn Nielsen, Auteur ; Bjarne Børresen, Auteur Année de publication : 2013 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : rotation;  flow  (dynamics);  pump  turbines;  pumps;  turbines;  blades;  geometry;  shapes Résumé : Characteristics of a reversible-pump turbine have been measured with five different leading edge profiles in turbine mode. These profiles varied the inlet blade angle and the radius of curvature. Further geometry parameters have been investigated through numerical simulations. The pump turbine tested has much steeper flow-speed characteristics than a comparable Francis turbine. The most obvious geometry difference is the inlet part of the runner blades, where the blade angle for the pump turbine is much smaller than for the Francis turbine. Two different blade angles have been tested on a physical model and computational fluid dynamics (CFD) simulations have been performed on four different angles. Both methods show that a smaller blade angle gives less steep characteristics in turbine mode, whereas the measured s-shape in turbine brake- and turbine pumping mode gets more exaggerated. Long-radius leading edges result in less steep characteristics. The unstable pump turbine characteristics are in the literature shown to be a result of vortex formation in the runner and guide vane channels. A leading edge with longer curvature radius moves the formation of vortices towards higher speed of rotation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Dependency on runner geometry for reversible-pump turbine characteristics in turbine mode of operation [texte imprimé] / Grunde Olimstad, Auteur ; Torbjørn Nielsen, Auteur ; Bjarne Børresen, Auteur . - 2013 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Mots-clés : rotation;  flow  (dynamics);  pump  turbines;  pumps;  turbines;  blades;  geometry;  shapes Résumé : Characteristics of a reversible-pump turbine have been measured with five different leading edge profiles in turbine mode. These profiles varied the inlet blade angle and the radius of curvature. Further geometry parameters have been investigated through numerical simulations. The pump turbine tested has much steeper flow-speed characteristics than a comparable Francis turbine. The most obvious geometry difference is the inlet part of the runner blades, where the blade angle for the pump turbine is much smaller than for the Francis turbine. Two different blade angles have been tested on a physical model and computational fluid dynamics (CFD) simulations have been performed on four different angles. Both methods show that a smaller blade angle gives less steep characteristics in turbine mode, whereas the measured s-shape in turbine brake- and turbine pumping mode gets more exaggerated. Long-radius leading edges result in less steep characteristics. The unstable pump turbine characteristics are in the literature shown to be a result of vortex formation in the runner and guide vane channels. A leading edge with longer curvature radius moves the formation of vortices towards higher speed of rotation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

URANS calculations for smooth circular cylinder flow in a wide range of Reynolds numbers / Guilherme F. Rosetti in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 18 p. Titre : URANS calculations for smooth circular cylinder flow in a wide range of Reynolds numbers : solution verification and validation Type de document : texte imprimé Auteurs : Guilherme F. Rosetti, Auteur ; Guilherme Vaz, Auteur ; André L. C. Fujarra, Auteur Année de publication : 2013 Article en page(s) : 18 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  separation  (technology);  turbulence;  eddies  (fluid  dynamics);  suction;  drag  (fluid  dynamics);  Reynolds  number;  shear  (mechanics);  wakes;  boundary  layers;  modeling;  cylinders;  errors;  uncertainty Résumé : The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply verification & validation (V&V) procedures to draw conclusions regarding numerical error and, afterwards, assess the modeling errors and capabilities of this (U)RANS method to solve the problem. Eight Reynolds numbers between Re = 10 and Re=5×105 will be presented with, at least, four geometrically similar grids and five discretization in time for each case (when unsteady), together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. Two-dimensional RANS, steady or unsteady, laminar or turbulent calculations are performed. The original 1994 k-ω SST turbulence model by Menter is used to model turbulence. The validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] URANS calculations for smooth circular cylinder flow in a wide range of Reynolds numbers : solution verification and validation [texte imprimé] / Guilherme F. Rosetti, Auteur ; Guilherme Vaz, Auteur ; André L. C. Fujarra, Auteur . - 2013 . - 18 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 18 p. Mots-clés : flow  (dynamics);  separation  (technology);  turbulence;  eddies  (fluid  dynamics);  suction;  drag  (fluid  dynamics);  Reynolds  number;  shear  (mechanics);  wakes;  boundary  layers;  modeling;  cylinders;  errors;  uncertainty Résumé : The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply verification & validation (V&V) procedures to draw conclusions regarding numerical error and, afterwards, assess the modeling errors and capabilities of this (U)RANS method to solve the problem. Eight Reynolds numbers between Re = 10 and Re=5×105 will be presented with, at least, four geometrically similar grids and five discretization in time for each case (when unsteady), together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. Two-dimensional RANS, steady or unsteady, laminar or turbulent calculations are performed. The original 1994 k-ω SST turbulence model by Menter is used to model turbulence. The validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Plasma control for a maneuvering low-aspect-ratio wing at low Reynolds number / Donald P. Rizzetta in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 19 p. Titre : Plasma control for a maneuvering low-aspect-ratio wing at low Reynolds number Type de document : texte imprimé Auteurs : Donald P. Rizzetta, Auteur ; Miguel R. Visbal, Auteur Année de publication : 2013 Article en page(s) : 19 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  flow  (dynamics);  aerodynamics;  fluids;  motion;  eddies  (fluid  dynamics);  Reynolds  number;  plasmas  (ionized  gases);  plasma  confinement;  chords  (trusses);  actuators;  computation;  wings Résumé : Plasma-based flow control was explored as a means of enhancing the performance of a maneuvering flat-plate wing. For this purpose, a numerical investigation was conducted via large-eddy simulation (LES). The wing has a rectangular planform, a thickness to chord ratio of 0.016, and an aspect ratio of 2.0. Computations were carried out at a chord-based Reynolds number of 20,000, such that the configuration and flow conditions are typical of those commonly utilized in a small unmanned air system (UAS). Solutions were obtained to the Navier–Stokes equations, that were augmented by source terms used to represent body forces imparted by plasma actuators on the fluid. A simple phenomenological model provided these body forces resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity time-implicit scheme and an implicit LES approach, which were applied to obtain solutions on an overset mesh system. Specific maneuvers considered in the investigation all began at 0 deg angle of attack, and consisted of a pitch-up and return, a pitch-up and hold, and a pitch-up to 60 deg. The maximum angle of attack for the first two maneuvers was 35 deg, which is well above that for static stall. Two different pitch rates were imposed for each of the specified motions. In control situations, a plasma actuator was distributed in the spanwise direction along the wing leading edge, or extended in the chordwise direction along the wing tip. Control solutions were compared with baseline results without actuation in order to assess the benefits of flow control and to determine its effectiveness. In all cases, it was found that plasma control can appreciably improve the time integrated lift over the duration of the maneuvers. The wing-tip actuator could achieve up to a 40% increase in the integrated lift, above that of the baseline value. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Plasma control for a maneuvering low-aspect-ratio wing at low Reynolds number [texte imprimé] / Donald P. Rizzetta, Auteur ; Miguel R. Visbal, Auteur . - 2013 . - 19 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 19 p. Mots-clés : force;  flow  (dynamics);  aerodynamics;  fluids;  motion;  eddies  (fluid  dynamics);  Reynolds  number;  plasmas  (ionized  gases);  plasma  confinement;  chords  (trusses);  actuators;  computation;  wings Résumé : Plasma-based flow control was explored as a means of enhancing the performance of a maneuvering flat-plate wing. For this purpose, a numerical investigation was conducted via large-eddy simulation (LES). The wing has a rectangular planform, a thickness to chord ratio of 0.016, and an aspect ratio of 2.0. Computations were carried out at a chord-based Reynolds number of 20,000, such that the configuration and flow conditions are typical of those commonly utilized in a small unmanned air system (UAS). Solutions were obtained to the Navier–Stokes equations, that were augmented by source terms used to represent body forces imparted by plasma actuators on the fluid. A simple phenomenological model provided these body forces resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity time-implicit scheme and an implicit LES approach, which were applied to obtain solutions on an overset mesh system. Specific maneuvers considered in the investigation all began at 0 deg angle of attack, and consisted of a pitch-up and return, a pitch-up and hold, and a pitch-up to 60 deg. The maximum angle of attack for the first two maneuvers was 35 deg, which is well above that for static stall. Two different pitch rates were imposed for each of the specified motions. In control situations, a plasma actuator was distributed in the spanwise direction along the wing leading edge, or extended in the chordwise direction along the wing tip. Control solutions were compared with baseline results without actuation in order to assess the benefits of flow control and to determine its effectiveness. In all cases, it was found that plasma control can appreciably improve the time integrated lift over the duration of the maneuvers. The wing-tip actuator could achieve up to a 40% increase in the integrated lift, above that of the baseline value. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Characteristics of turbulent wakes generated by twin parallel cylinders / M. A. Nosier in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 10 p. Titre : Characteristics of turbulent wakes generated by twin parallel cylinders Type de document : texte imprimé Auteurs : M. A. Nosier, Auteur ; A. R. Elbaz, Auteur ; T. N. Aboul Fetouh, Auteur Année de publication : 2013 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence;  wakes;  cylinders Résumé : This research aims to study the characteristics of the wake generated by twin cylinders. The cylinders are arranged in parallel side-by-side and staggered arrangements. The mainstream velocity is varied between 18 m/s and 20 m/s, which are equivalent to cylinder Reynolds numbers between 4750 and 5300. The cross-stream spacing ratios are 2, 3, 4, and 6 times the cylinder's diameter for the side-by-side arrangements. For the staggered arrangement, the cross-stream and streamwise spacing were varied between 2 and 4 times the cylinder diameter. The results show that the spacing ratio s/d has a significant effect on the wake development and interactions. The wakes of the side-by-side cylinders tend to merge into a single wake for cross-stream spacing of 2d and 3d at early stations, equivalent to 15 and 30 times the cylinder diameter, respectively, and merge completely at 50 and 100 times the cylinder diameter for 4d and 6d, respectively. Velocity measurements are used to develop a correlation that relates the wake merging distance to the cylinder spacing. Turbulence measurements are used to develop a correlation between the turbulence intensity and the streamwise distance. The comprehensive survey of the results and the correlations developed are provided in order to facilitate numerical model development and evaluation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Characteristics of turbulent wakes generated by twin parallel cylinders [texte imprimé] / M. A. Nosier, Auteur ; A. R. Elbaz, Auteur ; T. N. Aboul Fetouh, Auteur . - 2013 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 10 p. Mots-clés : flow  (dynamics);  turbulence;  wakes;  cylinders Résumé : This research aims to study the characteristics of the wake generated by twin cylinders. The cylinders are arranged in parallel side-by-side and staggered arrangements. The mainstream velocity is varied between 18 m/s and 20 m/s, which are equivalent to cylinder Reynolds numbers between 4750 and 5300. The cross-stream spacing ratios are 2, 3, 4, and 6 times the cylinder's diameter for the side-by-side arrangements. For the staggered arrangement, the cross-stream and streamwise spacing were varied between 2 and 4 times the cylinder diameter. The results show that the spacing ratio s/d has a significant effect on the wake development and interactions. The wakes of the side-by-side cylinders tend to merge into a single wake for cross-stream spacing of 2d and 3d at early stations, equivalent to 15 and 30 times the cylinder diameter, respectively, and merge completely at 50 and 100 times the cylinder diameter for 4d and 6d, respectively. Velocity measurements are used to develop a correlation that relates the wake merging distance to the cylinder spacing. Turbulence measurements are used to develop a correlation between the turbulence intensity and the streamwise distance. The comprehensive survey of the results and the correlations developed are provided in order to facilitate numerical model development and evaluation. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Turbulent flow in D-type corrugated pipes / H. Stel in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Titre : Turbulent flow in D-type corrugated pipes : flow pattern and friction factor Type de document : texte imprimé Auteurs : H. Stel, Auteur ; A. T. Franco, Auteur ; S. L. M. Junqueira, Auteur Année de publication : 2013 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  friction;  turbulence;  Reynolds  number;  pipes Résumé : Turbulent flow in d-type corrugated pipes of various aspect ratios has been numerically investigated in terms of flow pattern and friction factor, for Reynolds numbers ranging from 5000 to 100,000. The present numerical model was verified by comparing the friction factor with experimental and numerical results from the literature. The numerical analysis suggested that d-type behavior exists for groove aspect ratios up to w/k = (groove width/rib height) = 2 independent of the pitch. However, for a ratio of w/k = 3 an important change in the flow pattern occurs so that the pressure drag exerted by the groove walls becomes important. It is shown that the friction factor is independent of the groove height as long as the flow is similar to a flow in a d-type corrugated pipe. Moreover, the friction factor curve for d-type pipes shows a logarithmic behavior as function of the Reynolds number, so that a simple method can be used to derive an expression for the friction factor as a function of the Reynolds number and the relative groove width only. The results may be useful to engineering projects that require a better prediction of the friction factor in d-type corrugated pipes. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Turbulent flow in D-type corrugated pipes : flow pattern and friction factor [texte imprimé] / H. Stel, Auteur ; A. T. Franco, Auteur ; S. L. M. Junqueira, Auteur . - 2013 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Mots-clés : flow  (dynamics);  friction;  turbulence;  Reynolds  number;  pipes Résumé : Turbulent flow in d-type corrugated pipes of various aspect ratios has been numerically investigated in terms of flow pattern and friction factor, for Reynolds numbers ranging from 5000 to 100,000. The present numerical model was verified by comparing the friction factor with experimental and numerical results from the literature. The numerical analysis suggested that d-type behavior exists for groove aspect ratios up to w/k = (groove width/rib height) = 2 independent of the pitch. However, for a ratio of w/k = 3 an important change in the flow pattern occurs so that the pressure drag exerted by the groove walls becomes important. It is shown that the friction factor is independent of the groove height as long as the flow is similar to a flow in a d-type corrugated pipe. Moreover, the friction factor curve for d-type pipes shows a logarithmic behavior as function of the Reynolds number, so that a simple method can be used to derive an expression for the friction factor as a function of the Reynolds number and the relative groove width only. The results may be useful to engineering projects that require a better prediction of the friction factor in d-type corrugated pipes. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Thermal instability of Rivlin–Ericksen elastico-viscous nanofluid saturated by a porous medium / Ramesh Chand in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 07 p. Titre : Thermal instability of Rivlin–Ericksen elastico-viscous nanofluid saturated by a porous medium Type de document : texte imprimé Auteurs : Ramesh Chand, Auteur ; G. C. Rana, Auteur Année de publication : 2013 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Fluids,  Porous  materials,  Viscoelasticity,  Waves,  Rayleigh  number,  Nanoparticles,  Convection,  Nanofluids Résumé : Thermal instability in a horizontal layer of Rivlin–Ericksen elastico-viscous nanofluid in a porous medium is considered. A linear stability analysis based upon normal mode analysis is used to find a solution of the fluid layer confined between two free boundaries. The onset criterion for stationary and oscillatory convection is derived analytically and graphs have been plotted by giving numerical values to various parameters to depict the stability characteristics. The effects of the concentration Rayleigh number, Vadasz number, capacity ratio, Lewis number, and kinematics viscoelasticity parameter on the stability of the system are investigated. Regimes of oscillatory and nonoscillatory convection for various parameters are derived and discussed in detail. The sufficient conditions for the nonexistence of oscillatory convection have also been obtained. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Thermal instability of Rivlin–Ericksen elastico-viscous nanofluid saturated by a porous medium [texte imprimé] / Ramesh Chand, Auteur ; G. C. Rana, Auteur . - 2013 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 07 p. Mots-clés : Fluids,  Porous  materials,  Viscoelasticity,  Waves,  Rayleigh  number,  Nanoparticles,  Convection,  Nanofluids Résumé : Thermal instability in a horizontal layer of Rivlin–Ericksen elastico-viscous nanofluid in a porous medium is considered. A linear stability analysis based upon normal mode analysis is used to find a solution of the fluid layer confined between two free boundaries. The onset criterion for stationary and oscillatory convection is derived analytically and graphs have been plotted by giving numerical values to various parameters to depict the stability characteristics. The effects of the concentration Rayleigh number, Vadasz number, capacity ratio, Lewis number, and kinematics viscoelasticity parameter on the stability of the system are investigated. Regimes of oscillatory and nonoscillatory convection for various parameters are derived and discussed in detail. The sufficient conditions for the nonexistence of oscillatory convection have also been obtained. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Dual-frequency severe slugging in horizontal pipeline-riser systems / Reza Malekzadeh in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Titre : Dual-frequency severe slugging in horizontal pipeline-riser systems Type de document : texte imprimé Auteurs : Reza Malekzadeh, Auteur ; Robert F. Mudde, Auteur ; Ruud A. W. M. Henkes, Auteur Année de publication : 2013 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : oscillations;  flow  (dynamics);  pipelines;  pipeline  risers;  water Résumé : A new type of severe slugging is found that can occur in two-phase flow of gas and liquid in pipeline-riser systems. This instability, which will be referred to as dual-frequency severe slugging (DFSS), generates a different class of flow oscillations compared to the classical severe slugging cycle, having a dominant single frequency that is commonly found in a pipe downward inclined by a few degrees from the horizontal connected to a vertical riser. The DFSS flow pattern was found in laboratory experiments carried out in a 100 m long, 50.8 mm diameter horizontal pipeline followed by a 15 m high, 50.8 mm diameter vertical riser operating at atmospheric end pressure. The experimental facility also included a 400 liter gas buffer vessel, placed upstream of the pipeline, to obtain extra pipeline compressibility. Air and water were used as the experimental fluids. At constant inflow conditions, we observed a type of severe slugging exhibiting a dual-frequency behavior. The relatively high-frequency fluctuations, which are in the order of 0.01 Hz, are related to the classical severe slugging cycle or to an unstable oscillatory process. The relatively low-frequency fluctuations, which are in the order of 0.001 Hz, are associated with the gradual cyclic transition of the system between two metastable states, i.e., severe slugging and unstable oscillations. Numerical simulations were performed using OLGA, a one-dimensional two-fluid flow model. The numerical model predicts the relatively low-frequency fluctuations associated with the DFSS flow regime. The laboratory experiments and the numerical simulations showed that the evolution of the DFSS is proportional to the length of the pipeline. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Dual-frequency severe slugging in horizontal pipeline-riser systems [texte imprimé] / Reza Malekzadeh, Auteur ; Robert F. Mudde, Auteur ; Ruud A. W. M. Henkes, Auteur . - 2013 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 09 p. Mots-clés : oscillations;  flow  (dynamics);  pipelines;  pipeline  risers;  water Résumé : A new type of severe slugging is found that can occur in two-phase flow of gas and liquid in pipeline-riser systems. This instability, which will be referred to as dual-frequency severe slugging (DFSS), generates a different class of flow oscillations compared to the classical severe slugging cycle, having a dominant single frequency that is commonly found in a pipe downward inclined by a few degrees from the horizontal connected to a vertical riser. The DFSS flow pattern was found in laboratory experiments carried out in a 100 m long, 50.8 mm diameter horizontal pipeline followed by a 15 m high, 50.8 mm diameter vertical riser operating at atmospheric end pressure. The experimental facility also included a 400 liter gas buffer vessel, placed upstream of the pipeline, to obtain extra pipeline compressibility. Air and water were used as the experimental fluids. At constant inflow conditions, we observed a type of severe slugging exhibiting a dual-frequency behavior. The relatively high-frequency fluctuations, which are in the order of 0.01 Hz, are related to the classical severe slugging cycle or to an unstable oscillatory process. The relatively low-frequency fluctuations, which are in the order of 0.001 Hz, are associated with the gradual cyclic transition of the system between two metastable states, i.e., severe slugging and unstable oscillations. Numerical simulations were performed using OLGA, a one-dimensional two-fluid flow model. The numerical model predicts the relatively low-frequency fluctuations associated with the DFSS flow regime. The laboratory experiments and the numerical simulations showed that the evolution of the DFSS is proportional to the length of the pipeline. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Hydrodynamics of jets from guillotine steam generator tube rupture / J. L. Muñoz-Cobo in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 12 (Décembre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 11 p. Titre : Hydrodynamics of jets from guillotine steam generator tube rupture : modeling, analytical results, computational fluid dynamics calculation, and comparison with experimental data Type de document : texte imprimé Auteurs : J. L. Muñoz-Cobo, Auteur ; L. E. Herranz, Auteur ; A. Escrivá, Auteur Année de publication : 2013 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : momentum;  hydrodynamics;  stress;  jets;  trajectories  (physics);  boilers;  computational  fluid  dynamics;  modeling;  equations;  rupture;  outflow Résumé : In this work we study the hydrodynamics of characteristic gas jets resulting from guillotine breaks of steam generator tube rupture sequences (SGTR) in pressurized nuclear power reactors. As an initial step towards describing an “in-bundle” gas jet, a hydrodynamic model of free gas jets emerging from a guillotine break under prototypical SGTR conditions has been developed. First we have studied the jet characteristic for an isolated tube; the analytical model estimates variables such as trajectories, centerline velocities, velocity distribution, and Reynolds stresses. We have performed model comparisons with experimental data for different experimental conditions with different mass flow rates, and we have found good agreement of the model with the experimental results. Additionally, an “ad hoc” expression has been derived for the centerline jet velocity, which has been experimentally confirmed. Consistently with the experimental data and the computational fluid dynamics (CFD) calculations the analytical model predicts no outflow near the jet center. As a complementary issue, we have performed CFD calculations for a guillotine tube rupture when the tube is surrounded by several rows of neighboring tubes, in this case the jet trajectories are affected by the Coanda effect near the tubes. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Hydrodynamics of jets from guillotine steam generator tube rupture : modeling, analytical results, computational fluid dynamics calculation, and comparison with experimental data [texte imprimé] / J. L. Muñoz-Cobo, Auteur ; L. E. Herranz, Auteur ; A. Escrivá, Auteur . - 2013 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 12 (Décembre 2012) . - 11 p. Mots-clés : momentum;  hydrodynamics;  stress;  jets;  trajectories  (physics);  boilers;  computational  fluid  dynamics;  modeling;  equations;  rupture;  outflow Résumé : In this work we study the hydrodynamics of characteristic gas jets resulting from guillotine breaks of steam generator tube rupture sequences (SGTR) in pressurized nuclear power reactors. As an initial step towards describing an “in-bundle” gas jet, a hydrodynamic model of free gas jets emerging from a guillotine break under prototypical SGTR conditions has been developed. First we have studied the jet characteristic for an isolated tube; the analytical model estimates variables such as trajectories, centerline velocities, velocity distribution, and Reynolds stresses. We have performed model comparisons with experimental data for different experimental conditions with different mass flow rates, and we have found good agreement of the model with the experimental results. Additionally, an “ad hoc” expression has been derived for the centerline jet velocity, which has been experimentally confirmed. Consistently with the experimental data and the computational fluid dynamics (CFD) calculations the analytical model predicts no outflow near the jet center. As a complementary issue, we have performed CFD calculations for a guillotine tube rupture when the tube is surrounded by several rows of neighboring tubes, in this case the jet trajectories are affected by the Coanda effect near the tubes. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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