Dépouillements

Improvement of the performance of a centrifugal compressor by modifying the volute inlet / Semi Kim in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Titre : Improvement of the performance of a centrifugal compressor by modifying the volute inlet Type de document : texte imprimé Auteurs : Semi Kim, Auteur ; Park, Junyoung, Auteur ; Kukyoung Ahn, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  compressors;  impellers;  diffusers;  design Résumé : In centrifugal compressors, the diffuser and the volute have strong influences on the flow discharged from the impeller and thus also on the performance. In particular, a key parameter is the radial velocity at the volute inlet; it determines the swirl velocity, which is dissipated as a loss, i.e., it results in performance degradation. With the aim of reducing the swirl loss, a new type of volute with a modified inlet height was tested in this study. The volute inlet height was modified to 6 mm and 7 mm from the original height of 5 mm. The reliability of our computations was tested by comparison of the results of a model with this original height with experimental data. Flow analyses were conducted not only at the design mass flow rate but also at lower and higher mass flow rates. A higher total-to-total efficiency was obtained as a result of the linear increases of the volute inlet height from the diffuser outlet to 6 mm and 7 mm. Our detailed investigation of the simulated flow fields shows that the flow characteristics for a volute inlet height of 6 mm are better than those for a volute inlet height of 5 mm. These results clearly show that a greater volute inlet height assists in pressure recovery and reduces swirl loss in the volute. However, the volute inlet height of 7 mm results in larger hub separation and more energy loss, and thus in inferior performance. Therefore, the hub separation and the radial velocity at the volute inlet strongly influence the performance. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Improvement of the performance of a centrifugal compressor by modifying the volute inlet [texte imprimé] / Semi Kim, Auteur ; Park, Junyoung, Auteur ; Kukyoung Ahn, Auteur . - 2011 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  compressors;  impellers;  diffusers;  design Résumé : In centrifugal compressors, the diffuser and the volute have strong influences on the flow discharged from the impeller and thus also on the performance. In particular, a key parameter is the radial velocity at the volute inlet; it determines the swirl velocity, which is dissipated as a loss, i.e., it results in performance degradation. With the aim of reducing the swirl loss, a new type of volute with a modified inlet height was tested in this study. The volute inlet height was modified to 6 mm and 7 mm from the original height of 5 mm. The reliability of our computations was tested by comparison of the results of a model with this original height with experimental data. Flow analyses were conducted not only at the design mass flow rate but also at lower and higher mass flow rates. A higher total-to-total efficiency was obtained as a result of the linear increases of the volute inlet height from the diffuser outlet to 6 mm and 7 mm. Our detailed investigation of the simulated flow fields shows that the flow characteristics for a volute inlet height of 6 mm are better than those for a volute inlet height of 5 mm. These results clearly show that a greater volute inlet height assists in pressure recovery and reduces swirl loss in the volute. However, the volute inlet height of 7 mm results in larger hub separation and more energy loss, and thus in inferior performance. Therefore, the hub separation and the radial velocity at the volute inlet strongly influence the performance. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Dynamic modeling of hydrokinetic energy extraction / Veronica B. Miller in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Titre : Dynamic modeling of hydrokinetic energy extraction Type de document : texte imprimé Auteurs : Veronica B. Miller, Auteur ; Laura A. Schaefer, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  computational  fluid  dynamics;  turbines;  rivers;  hydropower;  dynamic  modeling Résumé : The world is facing an imminent energy crisis. In order to sustain our energy supply, it is necessary to advance renewable technologies. Despite this urgency, however, it is paramount to consider the larger environmental effects associated with using renewable resources. Hydropower, in the past, has been seen as a viable resource to examine, given that its basics of mechanical to electrical energy conversion seem to have little effect on the environment. Discrete analysis of dams and in-stream diversion set-ups, although, has shown otherwise. Modifications to river flows and changes in temperature (from increased and decreased flows) cause adverse effects to fish and other marine life because of changes in their adaptive habitat. Recent research has focused on kinetic energy extraction in river flows, which may prove to be more sustainable, as this type of extraction does not involve a large reservoir or large flow modification. The field of hydrokinetic energy extraction is immature; little is known about the devices’ performance in the river environment and their risk of impingement, fouling, and suspension of sediments. The governing principles of hydrokinetic energy extraction are presented, along with a two-dimensional computational fluid dynamics (CFD) model of the system. Power extraction methods are compared and CFD model validation is presented. It is clear that more research is required in hydrokinetic energy extraction with an emphasis toward lower environmental and ecological impacts. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Dynamic modeling of hydrokinetic energy extraction [texte imprimé] / Veronica B. Miller, Auteur ; Laura A. Schaefer, Auteur . - 2011 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Mots-clés : flow  (dynamics);  computational  fluid  dynamics;  turbines;  rivers;  hydropower;  dynamic  modeling Résumé : The world is facing an imminent energy crisis. In order to sustain our energy supply, it is necessary to advance renewable technologies. Despite this urgency, however, it is paramount to consider the larger environmental effects associated with using renewable resources. Hydropower, in the past, has been seen as a viable resource to examine, given that its basics of mechanical to electrical energy conversion seem to have little effect on the environment. Discrete analysis of dams and in-stream diversion set-ups, although, has shown otherwise. Modifications to river flows and changes in temperature (from increased and decreased flows) cause adverse effects to fish and other marine life because of changes in their adaptive habitat. Recent research has focused on kinetic energy extraction in river flows, which may prove to be more sustainable, as this type of extraction does not involve a large reservoir or large flow modification. The field of hydrokinetic energy extraction is immature; little is known about the devices’ performance in the river environment and their risk of impingement, fouling, and suspension of sediments. The governing principles of hydrokinetic energy extraction are presented, along with a two-dimensional computational fluid dynamics (CFD) model of the system. Power extraction methods are compared and CFD model validation is presented. It is clear that more research is required in hydrokinetic energy extraction with an emphasis toward lower environmental and ecological impacts. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Impact of fan gap flow on the centrifugal impeller aerodynamics / Yu-Tai Lee in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 09 p. Titre : Impact of fan gap flow on the centrifugal impeller aerodynamics Type de document : texte imprimé Auteurs : Yu-Tai Lee, Auteur Année de publication : 2011 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  impellers;  blades Résumé : The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Impact of fan gap flow on the centrifugal impeller aerodynamics [texte imprimé] / Yu-Tai Lee, Auteur . - 2011 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 09 p. Mots-clés : flow  (dynamics);  impellers;  blades Résumé : The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

The application of eddy-viscosity stress limiters for modeling cross-flow separation / P. A. Gregory in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 22 p. Titre : The application of eddy-viscosity stress limiters for modeling cross-flow separation Type de document : texte imprimé Auteurs : P. A. Gregory, Auteur ; P. N. Joubert, Auteur ; M. S. Chong, Auteur Année de publication : 2011 Article en page(s) : 22 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  turbulence;  eddies  (fluid  dynamics);  viscosity;  stres;  wakes;  boundary  layers;  engineering  simulation;  Reynolds-averaged  Navier–Stokes  equations;  cross-flow Résumé : The ability of eddy-viscosity models to simulate the turbulent wake produced by cross-flow separation over a curved body of revolution is assessed. The results obtained using the standard k−ω model show excessive levels of turbulent kinetic energy k in the vicinity of the stagnation point at the nose of the body. Additionally, high levels of k are observed throughout the wake. Enforcing laminar flow upstream of the nose (which replicates the experimental apparatus more accurately) gives more accurate estimates of k throughout the flowfield. A stress limiter in the form of Durbin’s T-limit modification for eddy-viscosity models is implemented for the k−ω model, and its effect on the computed surface pressures, skin friction, and surface flow features is assessed. Additionally, the effect of the T-limit modification on both the mean flow and the turbulent flow quantities within the wake is also examined. The use of the T-limit modification gives significant improvements in predicted levels of turbulent kinetic energy and Reynolds stresses within the wake. However, predicted values of skin friction in regions of attached flow become up to 50% greater than the experimental values when the T-limit is used. This is due to higher values of near-wall turbulence being created with the T-limit. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] The application of eddy-viscosity stress limiters for modeling cross-flow separation [texte imprimé] / P. A. Gregory, Auteur ; P. N. Joubert, Auteur ; M. S. Chong, Auteur . - 2011 . - 22 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 22 p. Mots-clés : pressure;  flow  (dynamics);  separation  (technology);  turbulence;  eddies  (fluid  dynamics);  viscosity;  stres;  wakes;  boundary  layers;  engineering  simulation;  Reynolds-averaged  Navier–Stokes  equations;  cross-flow Résumé : The ability of eddy-viscosity models to simulate the turbulent wake produced by cross-flow separation over a curved body of revolution is assessed. The results obtained using the standard k−ω model show excessive levels of turbulent kinetic energy k in the vicinity of the stagnation point at the nose of the body. Additionally, high levels of k are observed throughout the wake. Enforcing laminar flow upstream of the nose (which replicates the experimental apparatus more accurately) gives more accurate estimates of k throughout the flowfield. A stress limiter in the form of Durbin’s T-limit modification for eddy-viscosity models is implemented for the k−ω model, and its effect on the computed surface pressures, skin friction, and surface flow features is assessed. Additionally, the effect of the T-limit modification on both the mean flow and the turbulent flow quantities within the wake is also examined. The use of the T-limit modification gives significant improvements in predicted levels of turbulent kinetic energy and Reynolds stresses within the wake. However, predicted values of skin friction in regions of attached flow become up to 50% greater than the experimental values when the T-limit is used. This is due to higher values of near-wall turbulence being created with the T-limit. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Critical Reynolds number in constant-acceleration pipe flow from an initial steady laminar state / Charles W. Knisely in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 04 p. Titre : Critical Reynolds number in constant-acceleration pipe flow from an initial steady laminar state Type de document : texte imprimé Auteurs : Charles W. Knisely, Auteur ; Kazuyoshi Nishihara, Auteur ; Manabu Iguchi, Auteur Année de publication : 2011 Article en page(s) : 04 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence;  Reynolds  number;  flow  visualization;  pipe  flow;  pipes;  visualization;  water Résumé : The transition to turbulence in a constant-acceleration pipe flow from an initial laminar state was investigated in a custom-made apparatus permitting visual access to the water flow in the pipe. The apparatus allowed both laser Doppler velocimetry measurements and flow visualization using a tracer. The experiment was carried out by accelerating the flow from a steady laminar state to a steady turbulent state. The relation between the critical Reynolds number for transition to turbulence and the acceleration was found to be similar to that in a constant-acceleration pipe flow started from rest. In addition, with increased acceleration, the turbulent transition was found to be delayed to higher Reynolds numbers using flow visualization with simultaneous laser Doppler velocimetry measurements. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Critical Reynolds number in constant-acceleration pipe flow from an initial steady laminar state [texte imprimé] / Charles W. Knisely, Auteur ; Kazuyoshi Nishihara, Auteur ; Manabu Iguchi, Auteur . - 2011 . - 04 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 04 p. Mots-clés : flow  (dynamics);  turbulence;  Reynolds  number;  flow  visualization;  pipe  flow;  pipes;  visualization;  water Résumé : The transition to turbulence in a constant-acceleration pipe flow from an initial laminar state was investigated in a custom-made apparatus permitting visual access to the water flow in the pipe. The apparatus allowed both laser Doppler velocimetry measurements and flow visualization using a tracer. The experiment was carried out by accelerating the flow from a steady laminar state to a steady turbulent state. The relation between the critical Reynolds number for transition to turbulence and the acceleration was found to be similar to that in a constant-acceleration pipe flow started from rest. In addition, with increased acceleration, the turbulent transition was found to be delayed to higher Reynolds numbers using flow visualization with simultaneous laser Doppler velocimetry measurements. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Comparison of Lagrangian and Eulerian simulations of slurry flows in a sudden expansion / P. Frawley in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 12 p. Titre : Comparison of Lagrangian and Eulerian simulations of slurry flows in a sudden expansion Type de document : texte imprimé Auteurs : P. Frawley, Auteur ; A. P. O’Mahony, Auteur ; M. Geron, Auteur Année de publication : 2011 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  fluids;  particulate  matter;  turbulence;  erosion;  modeling;  slurries;  boundary-value  problems;  equations Résumé : From a review of technical literature, it was not apparent if the Lagrangian or the Eulerian dispersed phase modeling approach was more valid to simulate dilute erosive slurry flow. In this study, both modeling approaches were employed and a comparative analysis of performances and accuracy between the two models was carried out. Due to an impossibility to define, for the Eulerian model already implemented in FLUENT , a set of boundary conditions consistent with the Lagrangian impulsive equations, an Eulerian dispersed phase model was integrated in the FLUENT code using subroutines and user-defined scalar equations. Numerical predictions obtained from the two different approaches for two-phase flow in a sudden expansion were compared with the measured data. Excellent agreement was attained between the predicted and observed fluid and particle velocity in the axial direction and for the kinetic energy. Erosion profiles in a sudden expansion computed using the Lagrangian scheme yielded good qualitative agreement with measured data and predicted a maximum impact angle of 29 deg at the fluid reattachment point. The Eulerian model was adversely affected by the reattachment of the fluid phase to the wall and the simulated erosion profiles were not in agreement with the Lagrangian or measured data. Furthermore, the Eulerian model under-predicted the Lagrangian impact angle at all locations except the reattachment point. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Comparison of Lagrangian and Eulerian simulations of slurry flows in a sudden expansion [texte imprimé] / P. Frawley, Auteur ; A. P. O’Mahony, Auteur ; M. Geron, Auteur . - 2011 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 12 p. Mots-clés : flow  (dynamics);  fluids;  particulate  matter;  turbulence;  erosion;  modeling;  slurries;  boundary-value  problems;  equations Résumé : From a review of technical literature, it was not apparent if the Lagrangian or the Eulerian dispersed phase modeling approach was more valid to simulate dilute erosive slurry flow. In this study, both modeling approaches were employed and a comparative analysis of performances and accuracy between the two models was carried out. Due to an impossibility to define, for the Eulerian model already implemented in FLUENT , a set of boundary conditions consistent with the Lagrangian impulsive equations, an Eulerian dispersed phase model was integrated in the FLUENT code using subroutines and user-defined scalar equations. Numerical predictions obtained from the two different approaches for two-phase flow in a sudden expansion were compared with the measured data. Excellent agreement was attained between the predicted and observed fluid and particle velocity in the axial direction and for the kinetic energy. Erosion profiles in a sudden expansion computed using the Lagrangian scheme yielded good qualitative agreement with measured data and predicted a maximum impact angle of 29 deg at the fluid reattachment point. The Eulerian model was adversely affected by the reattachment of the fluid phase to the wall and the simulated erosion profiles were not in agreement with the Lagrangian or measured data. Furthermore, the Eulerian model under-predicted the Lagrangian impact angle at all locations except the reattachment point. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

A three-dimensional resolved discrete particle method for studying particle wall collision in a viscous fluid / Zhi-Gang Feng in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Titre : A three-dimensional resolved discrete particle method for studying particle wall collision in a viscous fluid Type de document : texte imprimé Auteurs : Zhi-Gang Feng, Auteur ; Efstathios E. Michaelides, Auteur ; Shaolin Mao, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : fluids;  particulate  matter;  collisions  (physics) Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Particle collisions with the walls are very important in understanding the fluid-particle behavior near the walls and determining the boundary conditions of the particulate phases in two-fluid models. In this paper, we examine the velocity characteristics of several types of particles near solid walls by applying a resolved discrete particle method (RDPM), which also uses the immersed boundary approach to model the solid particles. We assume that the particles are spherical with an initial velocity that is prescribed. The particles are allowed to traverse part of the viscous fluid until they collide with the solid wall. The collision force on the particle is modeled by a soft-sphere collision scheme with a linear spring-dashpot system. The hydrodynamic force on the particle is solved directly from the RDPM. By following the trajectories of several particles, we investigate the effect of the collision model parameters to the dynamics of particle close to the wall. We report here the rebound velocity of the particle, the coefficient of restitution, and the particle slip velocity at the wall as functions of the collision parameters. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] A three-dimensional resolved discrete particle method for studying particle wall collision in a viscous fluid [texte imprimé] / Zhi-Gang Feng, Auteur ; Efstathios E. Michaelides, Auteur ; Shaolin Mao, Auteur . - 2011 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 07 p. Mots-clés : fluids;  particulate  matter;  collisions  (physics) Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Particle collisions with the walls are very important in understanding the fluid-particle behavior near the walls and determining the boundary conditions of the particulate phases in two-fluid models. In this paper, we examine the velocity characteristics of several types of particles near solid walls by applying a resolved discrete particle method (RDPM), which also uses the immersed boundary approach to model the solid particles. We assume that the particles are spherical with an initial velocity that is prescribed. The particles are allowed to traverse part of the viscous fluid until they collide with the solid wall. The collision force on the particle is modeled by a soft-sphere collision scheme with a linear spring-dashpot system. The hydrodynamic force on the particle is solved directly from the RDPM. By following the trajectories of several particles, we investigate the effect of the collision model parameters to the dynamics of particle close to the wall. We report here the rebound velocity of the particle, the coefficient of restitution, and the particle slip velocity at the wall as functions of the collision parameters. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Reynolds number dependence, scaling, and dynamics of turbulent boundary layers / Joseph C. Klewicki in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 9 (Septembre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 48 p. Titre : Reynolds number dependence, scaling, and dynamics of turbulent boundary layers Type de document : texte imprimé Auteurs : Joseph C. Klewicki, Auteur Année de publication : 2011 Article en page(s) : 48 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : dynamics  (mechanics);  flow  (dynamics);  motion;  turbulence;  Reynolds  number;  stress;  vorticity;  boundary  layers;  boundary  layer  turbulence;  equations Résumé : The past two decades (approximately 1990 to 2010) have witnessed an ever-quickening pace of new findings pertaining to the Reynolds number dependencies, scaling, and dynamics of turbulent boundary layer flows (and wall-bounded turbulent flows in general). Given this, an important objective of the present effort is to provide a review that enables researchers new to the field (e.g., graduate students) to gain an appreciation for, and an understanding of, the prevalent research themes currently under investigation. Thus, the emphasis is more on laying a contextual foundation rather than, for example, comprehensively reporting all of the research findings of the past 20 years. The review begins with a brief exposition of scaling concepts and the normalizing parameters used in exploring Reynolds number dependence. An overall focus of the effort is to describe the scaling problem in relation to the underlying behaviors of the governing transport equations. For this reason, a number of relevant equations are concisely presented. The technical challenges associated with reliably exploring Reynolds number dependence are nontrivial and are of central importance. Thus, a separate section is devoted to this topic. Similarly, since they factor importantly relative to understanding and organizing the data trends, the attributes, strengths, and weaknesses of the various theoretical approaches and models (both physical and mathematical) are briefly reviewed. The statistical data presented primarily focus on means and variances since these quantities most directly relate to the time-averaged equations. Recent results pertaining to the spatial structure of turbulent boundary layers provide a useful context for describing instantaneous dynamics, often involving coherent vortical motions and including the so-called inner/outer interaction. Overall, the cumulative evidence increasingly supports a paradigm in which the scaling behaviors of the statistical profiles stem from the existence of an internal hierarchy of motions that approach a dynamically self-similar state as the Reynolds number becomes large. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Reynolds number dependence, scaling, and dynamics of turbulent boundary layers [texte imprimé] / Joseph C. Klewicki, Auteur . - 2011 . - 48 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 9 (Septembre 2010) . - 48 p. Mots-clés : dynamics  (mechanics);  flow  (dynamics);  motion;  turbulence;  Reynolds  number;  stress;  vorticity;  boundary  layers;  boundary  layer  turbulence;  equations Résumé : The past two decades (approximately 1990 to 2010) have witnessed an ever-quickening pace of new findings pertaining to the Reynolds number dependencies, scaling, and dynamics of turbulent boundary layer flows (and wall-bounded turbulent flows in general). Given this, an important objective of the present effort is to provide a review that enables researchers new to the field (e.g., graduate students) to gain an appreciation for, and an understanding of, the prevalent research themes currently under investigation. Thus, the emphasis is more on laying a contextual foundation rather than, for example, comprehensively reporting all of the research findings of the past 20 years. The review begins with a brief exposition of scaling concepts and the normalizing parameters used in exploring Reynolds number dependence. An overall focus of the effort is to describe the scaling problem in relation to the underlying behaviors of the governing transport equations. For this reason, a number of relevant equations are concisely presented. The technical challenges associated with reliably exploring Reynolds number dependence are nontrivial and are of central importance. Thus, a separate section is devoted to this topic. Similarly, since they factor importantly relative to understanding and organizing the data trends, the attributes, strengths, and weaknesses of the various theoretical approaches and models (both physical and mathematical) are briefly reviewed. The statistical data presented primarily focus on means and variances since these quantities most directly relate to the time-averaged equations. Recent results pertaining to the spatial structure of turbulent boundary layers provide a useful context for describing instantaneous dynamics, often involving coherent vortical motions and including the so-called inner/outer interaction. Overall, the cumulative evidence increasingly supports a paradigm in which the scaling behaviors of the statistical profiles stem from the existence of an internal hierarchy of motions that approach a dynamically self-similar state as the Reynolds number becomes large. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse