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Ajouter le résultat dans votre panierPassive control around the two-dimensional square back ahmed body using porous devices / Charles-Henri Bruneau in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 6 (Juin 2008)
Titre : Passive control around the two-dimensional square back ahmed body using porous devices Type de document : texte imprimé Auteurs : Charles-Henri Bruneau, Auteur ; Iraj Mortazavi, Auteur ; Patrick Gilliéron, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Two-dimensional flows passive control square back Ahmed body Résumé : The control of two-dimensional flows around the square back Ahmed body is achieved by using porous devices added on some parts of the body. The square back Ahmed body is considered either in an open domain or on top of a road. The modeling of the flow in different media is performed by means of the penalization method. A good choice of the location of the porous interfaces yields a significant improvement of the aerodynamic quantities, especially for the square back body. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p.[article] Passive control around the two-dimensional square back ahmed body using porous devices [texte imprimé] / Charles-Henri Bruneau, Auteur ; Iraj Mortazavi, Auteur ; Patrick Gilliéron, Auteur . - 2009 . - 12 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p.
Mots-clés : Two-dimensional flows passive control square back Ahmed body Résumé : The control of two-dimensional flows around the square back Ahmed body is achieved by using porous devices added on some parts of the body. The square back Ahmed body is considered either in an open domain or on top of a road. The modeling of the flow in different media is performed by means of the penalization method. A good choice of the location of the porous interfaces yields a significant improvement of the aerodynamic quantities, especially for the square back body. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Computational investigation of torque on coaxial rotating cones Type de document : texte imprimé Auteurs : Steve Rapley, Auteur ; Carol Eastwick, Auteur ; Kathy Simmons, Auteur Année de publication : 2009 Article en page(s) : 14 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Taylor–Couette flow torque coaxial rotating cones Résumé : This article looks at a modification of Taylor–Couette flow, presenting a numerical investigation of the flow around a shrouded rotating cone, with and without throughflow, using the commercial computational fluid dynamics code FLUENT 6.2 and FLUENT 6.3 . The effects of varying the cone vertex angle and the gap width on the torque seen by the rotating cone are considered, as well as the effect of a forced throughflow. The performance of various turbulence models are considered, as well as the ability of common wall treatments/functions to capture the near-wall behavior. Close agreement is found between the numerical predictions and previous experimental work, carried out by Yamada and Ito (1979, “Frictional Resistance of Enclosed Rotating Cones With Superposed Throughflow ,” ASME J. Fluids Eng., 101, pp. 259–264; 1975, “On the Frictional Resistance of Enclosed Rotating Cones (1st Report, Frictional Moment and Observation of Flow With a Smooth Surface) ,” Bull. JSME, 18, pp. 1026–1034; 1976, “On the Frictional Resistance of Enclosed Rotating Cones (2nd Report, Effects of Surface Roughness) ,” Bull. JSME, 19, pp. 943–950). Limitations in the models are considered, and comparisons between two-dimensional axisymmetric models and three-dimensional models are made, with the three-dimensional models showing greater accuracy. The work leads to a methodology for modeling similar flow conditions to Taylor–Couette. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 14 p.[article] Computational investigation of torque on coaxial rotating cones [texte imprimé] / Steve Rapley, Auteur ; Carol Eastwick, Auteur ; Kathy Simmons, Auteur . - 2009 . - 14 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 14 p.
Mots-clés : Taylor–Couette flow torque coaxial rotating cones Résumé : This article looks at a modification of Taylor–Couette flow, presenting a numerical investigation of the flow around a shrouded rotating cone, with and without throughflow, using the commercial computational fluid dynamics code FLUENT 6.2 and FLUENT 6.3 . The effects of varying the cone vertex angle and the gap width on the torque seen by the rotating cone are considered, as well as the effect of a forced throughflow. The performance of various turbulence models are considered, as well as the ability of common wall treatments/functions to capture the near-wall behavior. Close agreement is found between the numerical predictions and previous experimental work, carried out by Yamada and Ito (1979, “Frictional Resistance of Enclosed Rotating Cones With Superposed Throughflow ,” ASME J. Fluids Eng., 101, pp. 259–264; 1975, “On the Frictional Resistance of Enclosed Rotating Cones (1st Report, Frictional Moment and Observation of Flow With a Smooth Surface) ,” Bull. JSME, 18, pp. 1026–1034; 1976, “On the Frictional Resistance of Enclosed Rotating Cones (2nd Report, Effects of Surface Roughness) ,” Bull. JSME, 19, pp. 943–950). Limitations in the models are considered, and comparisons between two-dimensional axisymmetric models and three-dimensional models are made, with the three-dimensional models showing greater accuracy. The work leads to a methodology for modeling similar flow conditions to Taylor–Couette. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Identification of flow structures on a LP turbine blade due to periodic passing wakes Type de document : texte imprimé Auteurs : S. Sarkar, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow structures low-pressure turbine Résumé : The paper describes the flow structures on the suction surface of a highly cambered low-pressure turbine (LPT) blade (T106 profile) subjected to periodic convective wakes. A separation bubble on the rear half of the suction side of the blade was found to form under the operating condition due to the highly diffusive boundary layer. Interactions of migrating wakes with this separated boundary layer trigger rollup of the shear layer leading to transition and the appearance of coherent vortices. To characterize the dynamics of these large-scale structures, a proper orthogonal decomposition is pursued on both the fluctuating velocity and the vorticity fields generated by large-eddy simulations (LESs) of wake passing over the LPT blade for a Reynolds number Re=1.6×105. The first two modes clearly depict the rollup of the unstable shear layer and formation of large-scale vortex loops that contain a major fraction of the fluctuation energy. The present LES, at least in a qualitative sense, illustrates the large-scale motions in the outer layer and dynamics of vortical structures in a separated boundary layer excited by external perturbations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 10 p.[article] Identification of flow structures on a LP turbine blade due to periodic passing wakes [texte imprimé] / S. Sarkar, Auteur . - 2009 . - 10 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 10 p.
Mots-clés : Flow structures low-pressure turbine Résumé : The paper describes the flow structures on the suction surface of a highly cambered low-pressure turbine (LPT) blade (T106 profile) subjected to periodic convective wakes. A separation bubble on the rear half of the suction side of the blade was found to form under the operating condition due to the highly diffusive boundary layer. Interactions of migrating wakes with this separated boundary layer trigger rollup of the shear layer leading to transition and the appearance of coherent vortices. To characterize the dynamics of these large-scale structures, a proper orthogonal decomposition is pursued on both the fluctuating velocity and the vorticity fields generated by large-eddy simulations (LESs) of wake passing over the LPT blade for a Reynolds number Re=1.6×105. The first two modes clearly depict the rollup of the unstable shear layer and formation of large-scale vortex loops that contain a major fraction of the fluctuation energy. The present LES, at least in a qualitative sense, illustrates the large-scale motions in the outer layer and dynamics of vortical structures in a separated boundary layer excited by external perturbations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Calculation of fluid flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer Type de document : texte imprimé Auteurs : Valery Ponyavin, Auteur ; Yitung Chen, Auteur ; James Cutts, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Fluid flow distribution heat exchanger Résumé : Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.[article] Calculation of fluid flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer [texte imprimé] / Valery Ponyavin, Auteur ; Yitung Chen, Auteur ; James Cutts, Auteur . - 2009 . - 8 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.
Mots-clés : Fluid flow distribution heat exchanger Résumé : Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Effect of interfacial waves on turbulence structure in stratified duct flows Type de document : texte imprimé Auteurs : M. Fernandino, Auteur ; T. Ytrehus, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Résumé : Stratified flows are encountered in many industrial applications. The determination of the flow characteristics is essential for the prediction of pressure drop and holdup in the system. The aim of this study is to gain insight into the interaction of a gas and a liquid phase flowing in a stratified regime, with especial focus on the effect of interfacial waves on the turbulence structure of the liquid phase. Measurements of mean velocities and turbulent intensities in the liquid phase of a stratified air-water duct flow are performed. Mean velocity profiles and turbulence structure are affected differently for different wave amplitudes. The effect of small amplitude waves is restricted to the near-interface region, resembling the effect of increasing shear rate on a flat interface. On the other hand, large amplitude waves modify the flow structure throughout the whole liquid depth. The mean velocity is greatly enhanced, resulting in a higher bulk velocity. Turbulent intensities are also significantly enhanced especially in the interface region. This big difference in flow structure is not observed after the appearance of the first waves but rather when a certain critical wave amplitude is triggered, indicating that the prediction of this critical wave type turns out to be more important than the determination of the transition from a smooth to a stratified wavy regime. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.[article] Effect of interfacial waves on turbulence structure in stratified duct flows [texte imprimé] / M. Fernandino, Auteur ; T. Ytrehus, Auteur . - 2009 . - 8 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.
Résumé : Stratified flows are encountered in many industrial applications. The determination of the flow characteristics is essential for the prediction of pressure drop and holdup in the system. The aim of this study is to gain insight into the interaction of a gas and a liquid phase flowing in a stratified regime, with especial focus on the effect of interfacial waves on the turbulence structure of the liquid phase. Measurements of mean velocities and turbulent intensities in the liquid phase of a stratified air-water duct flow are performed. Mean velocity profiles and turbulence structure are affected differently for different wave amplitudes. The effect of small amplitude waves is restricted to the near-interface region, resembling the effect of increasing shear rate on a flat interface. On the other hand, large amplitude waves modify the flow structure throughout the whole liquid depth. The mean velocity is greatly enhanced, resulting in a higher bulk velocity. Turbulent intensities are also significantly enhanced especially in the interface region. This big difference in flow structure is not observed after the appearance of the first waves but rather when a certain critical wave amplitude is triggered, indicating that the prediction of this critical wave type turns out to be more important than the determination of the transition from a smooth to a stratified wavy regime. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Influence of upstream conditions and gravity on highly inertial thin-film flow Type de document : texte imprimé Auteurs : Roger E. Khayat, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : thin-film flow Newtonian fluid Résumé : Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 13 p.[article] Influence of upstream conditions and gravity on highly inertial thin-film flow [texte imprimé] / Roger E. Khayat, Auteur . - 2009 . - 13 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 13 p.
Mots-clés : thin-film flow Newtonian fluid Résumé : Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : On the flutter and drag forces on flexible rectangular canopies in normal flow Type de document : texte imprimé Auteurs : Antonio Filippone, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flexible rectangular canopies aerodynamic drag slenderness varies Reynolds number Résumé : The paper presents results of experimental investigations on flexible rectangular canopies fixed at two edges (tapes). Data are presented for the aerodynamic drag as a function of the planform area, the slenderness, and the Reynolds number. The slenderness varies from 3.3 to 30. The Reynolds number is limited to 2×106. The wind speed is in the range 6–19m∕s. The results show that the drag decreases with the increasing aspect ratio. The dominant parameter is the slenderness; a second dominant factor is the planform area. The drag is only weakly dependent on the Reynolds number. The analysis of the drag data indicates that a proper scaling parameter is the crosswise length scale. When normalization is done, the data tend to collapse into a single curve. A further study addressed the drag characteristics of the canopies with perforated planforms. Perforation of up to 6% of the planform area has been considered. Corrections for air permeability of the fabric are introduced. The drag is reduced roughly linearly with perforated area. A detailed study into the flutter characteristics of the canopies in the turbulent wind is presented. The investigation has highlighted different modes of oscillations, including deformations through folding and twisting, vertical flapping, rotations, and cross-type oscillations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.[article] On the flutter and drag forces on flexible rectangular canopies in normal flow [texte imprimé] / Antonio Filippone, Auteur . - 2009 . - 8 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.
Mots-clés : Flexible rectangular canopies aerodynamic drag slenderness varies Reynolds number Résumé : The paper presents results of experimental investigations on flexible rectangular canopies fixed at two edges (tapes). Data are presented for the aerodynamic drag as a function of the planform area, the slenderness, and the Reynolds number. The slenderness varies from 3.3 to 30. The Reynolds number is limited to 2×106. The wind speed is in the range 6–19m∕s. The results show that the drag decreases with the increasing aspect ratio. The dominant parameter is the slenderness; a second dominant factor is the planform area. The drag is only weakly dependent on the Reynolds number. The analysis of the drag data indicates that a proper scaling parameter is the crosswise length scale. When normalization is done, the data tend to collapse into a single curve. A further study addressed the drag characteristics of the canopies with perforated planforms. Perforation of up to 6% of the planform area has been considered. Corrections for air permeability of the fabric are introduced. The drag is reduced roughly linearly with perforated area. A detailed study into the flutter characteristics of the canopies in the turbulent wind is presented. The investigation has highlighted different modes of oscillations, including deformations through folding and twisting, vertical flapping, rotations, and cross-type oscillations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Investigation of combined electro-osmotic and pressure-driven flow in rough microchannels Type de document : texte imprimé Auteurs : Prashant R. Waghmare, Auteur ; Sushanta K. Mitra, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : surface roughness electro-osmotic flow pressure-driven microchannel Résumé : The present study is carried out to investigate the influence of surface roughness in combined electro-osmotic and pressure-driven flow in microchannel. Two-dimensional theoretical model is developed to predict the behavior of velocity profiles in rough microchannel. The concept of surface roughness-viscosity model is used to account the effect of surface roughness. The pluglike velocity profile for electro-osmotic flow and the parabolic velocity profile for pressure-driven flow with delay in attaining the centerline velocity are observed. It is found that for electro-osmotic flow, the deviation in velocity profile from a flow in a smooth channel occurs near the wall, whereas in pressure-driven flow, such deviation is dominant in the core region. A superposition of pluglike and parabolic velocity profiles is found in combined electro-osmotic and pressure-driven flow. It is also observed that in the case of combined flow, the deviation in velocity profile from the smooth channel case reduces gradually with the distance from the wall. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.[article] Investigation of combined electro-osmotic and pressure-driven flow in rough microchannels [texte imprimé] / Prashant R. Waghmare, Auteur ; Sushanta K. Mitra, Auteur . - 2009 . - 8 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 8 p.
Mots-clés : surface roughness electro-osmotic flow pressure-driven microchannel Résumé : The present study is carried out to investigate the influence of surface roughness in combined electro-osmotic and pressure-driven flow in microchannel. Two-dimensional theoretical model is developed to predict the behavior of velocity profiles in rough microchannel. The concept of surface roughness-viscosity model is used to account the effect of surface roughness. The pluglike velocity profile for electro-osmotic flow and the parabolic velocity profile for pressure-driven flow with delay in attaining the centerline velocity are observed. It is found that for electro-osmotic flow, the deviation in velocity profile from a flow in a smooth channel occurs near the wall, whereas in pressure-driven flow, such deviation is dominant in the core region. A superposition of pluglike and parabolic velocity profiles is found in combined electro-osmotic and pressure-driven flow. It is also observed that in the case of combined flow, the deviation in velocity profile from the smooth channel case reduces gradually with the distance from the wall. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Entropy generation in the viscous parts of turbulent boundary layers Type de document : texte imprimé Auteurs : Mc Eligot, Donald M., Auteur ; Edmond J. Walsh, Auteur ; Eckart Laurien, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pointwise entropy turbulent boundary layers Résumé : The local (pointwise) entropy generation rate per unit volume S‴ is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S‴ differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area Sap″, agrees within 5% at its edge. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p.[article] Entropy generation in the viscous parts of turbulent boundary layers [texte imprimé] / Mc Eligot, Donald M., Auteur ; Edmond J. Walsh, Auteur ; Eckart Laurien, Auteur . - 2009 . - 12 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p.
Mots-clés : Pointwise entropy turbulent boundary layers Résumé : The local (pointwise) entropy generation rate per unit volume S‴ is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S‴ differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area Sap″, agrees within 5% at its edge. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : PIV study of separated and reattached open channel flow over surface mounted blocks Type de document : texte imprimé Auteurs : Martin Agelinchaab, Auteur ; Mark F. Tachie, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Turbulence stress shear (mechanics) open channels (hydraulics) flow (dynamics) boundary layers geometry thickness separation (technology) Résumé : A particle image velocimetry is used to study the mean and turbulent fields of separated and redeveloping flow over square, rectangular, and semicircular blocks fixed to the bottom wall of an open channel. The open channel flow is characterized by high background turbulence level, and the ratio of the upstream boundary layer thickness to block height is considerably higher than in prior experiments. The variation of the Reynolds stresses along the dividing streamlines is discussed within the context of vortex stretching, longitudinal strain rate, and wall damping. It appears that wall damping is a more dominant mechanism in the vicinity of reattachment. In the recirculation and reattachment regions, profiles of the mean velocity, turbulent quantities, and transport terms are used to document the salient features of block geometry on the flow. The flow characteristics in these regions strongly depend on block geometry. Downstream of reattachment, a new shear layer is formed, and the redevelopment of the shear layer toward the upstream open channel boundary layer is studied using the boundary layer parameters and Reynolds stresses. The results show that the mean flow rapidly redeveloped so that the Clauser parameter recovered to its upstream value at 90 step heights downstream of reattachment. However, the rate of development close to reattachment strongly depends on block geometry. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 9 p.[article] PIV study of separated and reattached open channel flow over surface mounted blocks [texte imprimé] / Martin Agelinchaab, Auteur ; Mark F. Tachie, Auteur . - 2009 . - 9 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 9 p.
Mots-clés : Turbulence stress shear (mechanics) open channels (hydraulics) flow (dynamics) boundary layers geometry thickness separation (technology) Résumé : A particle image velocimetry is used to study the mean and turbulent fields of separated and redeveloping flow over square, rectangular, and semicircular blocks fixed to the bottom wall of an open channel. The open channel flow is characterized by high background turbulence level, and the ratio of the upstream boundary layer thickness to block height is considerably higher than in prior experiments. The variation of the Reynolds stresses along the dividing streamlines is discussed within the context of vortex stretching, longitudinal strain rate, and wall damping. It appears that wall damping is a more dominant mechanism in the vicinity of reattachment. In the recirculation and reattachment regions, profiles of the mean velocity, turbulent quantities, and transport terms are used to document the salient features of block geometry on the flow. The flow characteristics in these regions strongly depend on block geometry. Downstream of reattachment, a new shear layer is formed, and the redevelopment of the shear layer toward the upstream open channel boundary layer is studied using the boundary layer parameters and Reynolds stresses. The results show that the mean flow rapidly redeveloped so that the Clauser parameter recovered to its upstream value at 90 step heights downstream of reattachment. However, the rate of development close to reattachment strongly depends on block geometry. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Numerical simulation of 3D cavitating flows : analysis of cavitation head drop in turbomachinery Type de document : texte imprimé Auteurs : Benoît Pouffary, Auteur ; Regiane Fortes Patella, Auteur ; Jean-Luc Reboud, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Cavitating flows cavitation team turbomachinery Résumé : The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Grenoble, France in collaboration with the French space agency (Centre National d’Etudes Spatiales, CNES), the rocket engine division of Snecma and Numeca International. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the CFD code FINE/TURBO ™. An analysis methodology allowing the numerical simulation of the head drop induced by the development of cavitation in cold water was proposed and applied in the case of two four-bladed inducers and one centrifugal pump. Global results were compared to available experimental results. Internal flows in turbomachinery were investigated in depth. Numerical simulations enabled the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 10 p.[article] Numerical simulation of 3D cavitating flows : analysis of cavitation head drop in turbomachinery [texte imprimé] / Benoît Pouffary, Auteur ; Regiane Fortes Patella, Auteur ; Jean-Luc Reboud, Auteur . - 2009 . - 10 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 10 p.
Mots-clés : Cavitating flows cavitation team turbomachinery Résumé : The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Grenoble, France in collaboration with the French space agency (Centre National d’Etudes Spatiales, CNES), the rocket engine division of Snecma and Numeca International. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the CFD code FINE/TURBO ™. An analysis methodology allowing the numerical simulation of the head drop induced by the development of cavitation in cold water was proposed and applied in the case of two four-bladed inducers and one centrifugal pump. Global results were compared to available experimental results. Internal flows in turbomachinery were investigated in depth. Numerical simulations enabled the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : A runback criterion for water drops in a turbulent accelerated boundary layer Type de document : texte imprimé Auteurs : Edward B. White, Auteur ; Jason A. Schmucker, Auteur Année de publication : 2009 Article en page(s) : 6 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Aerodynamic boundary layers runback threshold Résumé : Predicting the runback threshold for liquid drops in aerodynamic boundary layers is a challenging problem with numerous applications including aircraft icing simulations. The critical parameters that govern drop runback are investigated in this experiment by using a wind tunnel that provides a turbulent accelerated flow similar to flows near an unswept wing’s leading edge. The experiments feature water drops on aluminum with a contact angle of 70±5deg. Results show that significant water∕air interface unsteadiness precedes drop runback. This is likely due to air-flow separation in the drop wakes. For displacement-thickness-scaled Reynolds numbers ranging from 348 to 429, a constant-Weber-number runback threshold We=3.45±0.09 is found to adequately correlate the runback results. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 6 p.[article] A runback criterion for water drops in a turbulent accelerated boundary layer [texte imprimé] / Edward B. White, Auteur ; Jason A. Schmucker, Auteur . - 2009 . - 6 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 6 p.
Mots-clés : Aerodynamic boundary layers runback threshold Résumé : Predicting the runback threshold for liquid drops in aerodynamic boundary layers is a challenging problem with numerous applications including aircraft icing simulations. The critical parameters that govern drop runback are investigated in this experiment by using a wind tunnel that provides a turbulent accelerated flow similar to flows near an unswept wing’s leading edge. The experiments feature water drops on aluminum with a contact angle of 70±5deg. Results show that significant water∕air interface unsteadiness precedes drop runback. This is likely due to air-flow separation in the drop wakes. For displacement-thickness-scaled Reynolds numbers ranging from 348 to 429, a constant-Weber-number runback threshold We=3.45±0.09 is found to adequately correlate the runback results. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Effervescent atomization of viscoelastic liquids : experiment and modeling Type de document : texte imprimé Auteurs : S. C. Geckler, Auteur ; P. E. Sojka, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Fluids drops polymers sprays molecular weight water stability tension Résumé : The effervescent atomization of viscoelastic liquids is reported. A total of 23 fluids, formulated from a 60wt% glycerine/40wt% water solvent to which were added varying concentrations (0.001–0.5wt%) of poly(ethylene oxide) polymers whose molecular weights ranged from 12,000 to 900,000, were sprayed through a conventional effervescent atomizer. Mean drop sizes were measured using a forward light scattering instrument. The drop size (D32) data show the expected decrease with an increase in air-liquid ratio by mass (ALR), the expected increase with an increase in polymer concentration, plus an increase with an increase in polymer molecular weight for most cases. However, no significant change in D32 was observed for polymer solutions whose molecular weights ranged from 12,000 to 35,000, suggesting the presence of a critical molecular weight below which spray performance is unaltered. This argues for two different factors controlling drop size: Polymer molecular weight is most influential at the highest polymer concentrations while polymer concentration is most influential at the lowest polymer concentrations. Analysis of the spray formation process was carried out using a ligament formation model previously developed for the effervescent atomization of Newtonian liquids coupled with a linear stability model for the breakup of viscoelastic liquid jets. The jet breakup model assumes that an unrelaxed axial tension exists within the fluid. A comparison of model predictions and experimental data indicates that the model predicts the observed dependencies of mean drop size on ALR, polymer concentration, and polymer molecular weight. Quantitative agreement is within 10–50% of experimental values in all cases. Finally, a shortcoming of the model is noted and a means of avoiding this limitation reported. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 11 p.[article] Effervescent atomization of viscoelastic liquids : experiment and modeling [texte imprimé] / S. C. Geckler, Auteur ; P. E. Sojka, Auteur . - 2009 . - 11 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 11 p.
Mots-clés : Fluids drops polymers sprays molecular weight water stability tension Résumé : The effervescent atomization of viscoelastic liquids is reported. A total of 23 fluids, formulated from a 60wt% glycerine/40wt% water solvent to which were added varying concentrations (0.001–0.5wt%) of poly(ethylene oxide) polymers whose molecular weights ranged from 12,000 to 900,000, were sprayed through a conventional effervescent atomizer. Mean drop sizes were measured using a forward light scattering instrument. The drop size (D32) data show the expected decrease with an increase in air-liquid ratio by mass (ALR), the expected increase with an increase in polymer concentration, plus an increase with an increase in polymer molecular weight for most cases. However, no significant change in D32 was observed for polymer solutions whose molecular weights ranged from 12,000 to 35,000, suggesting the presence of a critical molecular weight below which spray performance is unaltered. This argues for two different factors controlling drop size: Polymer molecular weight is most influential at the highest polymer concentrations while polymer concentration is most influential at the lowest polymer concentrations. Analysis of the spray formation process was carried out using a ligament formation model previously developed for the effervescent atomization of Newtonian liquids coupled with a linear stability model for the breakup of viscoelastic liquid jets. The jet breakup model assumes that an unrelaxed axial tension exists within the fluid. A comparison of model predictions and experimental data indicates that the model predicts the observed dependencies of mean drop size on ALR, polymer concentration, and polymer molecular weight. Quantitative agreement is within 10–50% of experimental values in all cases. Finally, a shortcoming of the model is noted and a means of avoiding this limitation reported. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Some exact solutions to equations of motion of an incompressible third grade fluid Type de document : texte imprimé Auteurs : Saif Ullah, Auteur Année de publication : 2009 Article en page(s) : 5 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Incompressible third grade fluid Résumé : This investigation deals with some exact solutions of the equations governing the steady plane motions of an incompressible third grade fluid by using complex variables and complex functions. Some of the solutions admit, as particular cases, all the solutions of Moro [1990, “Steady Flows of a Third Grade Fluid by Transformation Methods ,” ZAMM, 70(3), pp. 189–198] En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 5 p.[article] Some exact solutions to equations of motion of an incompressible third grade fluid [texte imprimé] / Saif Ullah, Auteur . - 2009 . - 5 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 5 p.
Mots-clés : Incompressible third grade fluid Résumé : This investigation deals with some exact solutions of the equations governing the steady plane motions of an incompressible third grade fluid by using complex variables and complex functions. Some of the solutions admit, as particular cases, all the solutions of Moro [1990, “Steady Flows of a Third Grade Fluid by Transformation Methods ,” ZAMM, 70(3), pp. 189–198] En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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Titre : Passive control of transonic cavity flow Type de document : texte imprimé Auteurs : David G. MacManus, Auteur ; Diane S. Doran, Auteur Année de publication : 2009 Article en page(s) : 4 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Transonic cavity flow Résumé : Open cavities at transonic speeds can result in acoustic resonant flow behavior with fluctuating pressure levels of sufficient intensity to cause significant damage to internal stores and surrounding structures. Extensive research in this field has produced numerous cavity flow control techniques, the more effective of which may require costly feedback control systems or entail other drawbacks such as drag penalties or rapid performance degradation at off-design condition. The current study focuses on the use of simple geometric modifications of a rectangular planform cavity with the aim of attenuating the aeroacoustic signature. Experiments were performed in an intermittent suck-down transonic wind tunnel by using a typical open flow rectangular planform cavity, which was modularly designed such that the leading and trailing edge geometries could be modified by using a family of inserts. The current work focused on a variety of recessed leading edge step arrangements. Configurations were tested at transonic Mach numbers spanning the range Mach 0.7–0.9, and unsteady pressure measurements were recorded at various stations within the cavity in order to obtain acoustic spectra. The most effective configuration at Mach 0.9 was the leading edge step employing a step height to step length ratio of 0.4. This configuration achieved a tonal attenuation of up to 18.6dB and an overall sound pressure level (OASPL) reduction of approximately 7.5dB. This is a significant level of noise suppression in comparison with other passive control methods. In addition, it offers the additional benefits of being a simple geometric feature, which does not rely on placing flow effectors into the high-speed grazing flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 4 p.[article] Passive control of transonic cavity flow [texte imprimé] / David G. MacManus, Auteur ; Diane S. Doran, Auteur . - 2009 . - 4 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 4 p.
Mots-clés : Transonic cavity flow Résumé : Open cavities at transonic speeds can result in acoustic resonant flow behavior with fluctuating pressure levels of sufficient intensity to cause significant damage to internal stores and surrounding structures. Extensive research in this field has produced numerous cavity flow control techniques, the more effective of which may require costly feedback control systems or entail other drawbacks such as drag penalties or rapid performance degradation at off-design condition. The current study focuses on the use of simple geometric modifications of a rectangular planform cavity with the aim of attenuating the aeroacoustic signature. Experiments were performed in an intermittent suck-down transonic wind tunnel by using a typical open flow rectangular planform cavity, which was modularly designed such that the leading and trailing edge geometries could be modified by using a family of inserts. The current work focused on a variety of recessed leading edge step arrangements. Configurations were tested at transonic Mach numbers spanning the range Mach 0.7–0.9, and unsteady pressure measurements were recorded at various stations within the cavity in order to obtain acoustic spectra. The most effective configuration at Mach 0.9 was the leading edge step employing a step height to step length ratio of 0.4. This configuration achieved a tonal attenuation of up to 18.6dB and an overall sound pressure level (OASPL) reduction of approximately 7.5dB. This is a significant level of noise suppression in comparison with other passive control methods. In addition, it offers the additional benefits of being a simple geometric feature, which does not rely on placing flow effectors into the high-speed grazing flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] Exemplaires
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