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Ajouter le résultat dans votre panierAn experimental study of the laminar flow separation on a low-Reynolds-number airfoil / Hui, Hu in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 5 (Mai 2008)
Titre : An experimental study of the laminar flow separation on a low-Reynolds-number airfoil Type de document : texte imprimé Auteurs : Hui, Hu, Auteur ; Zifeng Yang, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Separation (technology) airfoils bubbles pressure boundary layers laminar flow flow (dynamics) drag (fluid dynamics) Résumé : An experimental study was conducted to characterize the transient behavior of laminar flow separation on a NASA low-speed GA (W)-1 airfoil at the chord Reynolds number of 70,000. In addition to measuring the surface pressure distribution around the airfoil, a high-resolution particle image velocimetry (PIV) system was used to make detailed flow field measurements to quantify the evolution of unsteady flow structures around the airfoil at various angles of attack (AOAs). The surface pressure and PIV measurements clearly revealed that the laminar boundary layer would separate from the airfoil surface, as the adverse pressure gradient over the airfoil upper surface became severe at AOA≥8.0deg. The separated laminar boundary layer was found to rapidly transit to turbulence by generating unsteady Kelvin–Helmholtz vortex structures. After turbulence transition, the separated boundary layer was found to reattach to the airfoil surface as a turbulent boundary layer when the adverse pressure gradient was adequate at AOA12.0deg. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 11 p.[article] An experimental study of the laminar flow separation on a low-Reynolds-number airfoil [texte imprimé] / Hui, Hu, Auteur ; Zifeng Yang, Auteur . - 2009 . - 11 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 11 p.
Mots-clés : Separation (technology) airfoils bubbles pressure boundary layers laminar flow flow (dynamics) drag (fluid dynamics) Résumé : An experimental study was conducted to characterize the transient behavior of laminar flow separation on a NASA low-speed GA (W)-1 airfoil at the chord Reynolds number of 70,000. In addition to measuring the surface pressure distribution around the airfoil, a high-resolution particle image velocimetry (PIV) system was used to make detailed flow field measurements to quantify the evolution of unsteady flow structures around the airfoil at various angles of attack (AOAs). The surface pressure and PIV measurements clearly revealed that the laminar boundary layer would separate from the airfoil surface, as the adverse pressure gradient over the airfoil upper surface became severe at AOA≥8.0deg. The separated laminar boundary layer was found to rapidly transit to turbulence by generating unsteady Kelvin–Helmholtz vortex structures. After turbulence transition, the separated boundary layer was found to reattach to the airfoil surface as a turbulent boundary layer when the adverse pressure gradient was adequate at AOA12.0deg. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Computational modeling and simulation of a single-jet water meter Type de document : texte imprimé Auteurs : Gorka S. Larraona, Auteur ; Alejandro Rivas, Auteur ; Juan Carlos Ramos, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Rotation flow (dynamics) turbines errors engineering simulation water meters torque Résumé : A single-jet water meter was modeled and simulated within a wide measuring range that included flow rates in laminar, transitional, and turbulent flow regimes. The interaction between the turbine and the flow, on which the operating principle of this kind of meter is based, was studied in depth from the detailed information provided by simulations of the three dimensional flow within the meter. This interaction was resolved by means of a devised semi-implicit time-marching procedure in such a way that the speed and the position of the turbine were obtained as part of the solution. Results obtained regarding the turbine’s mean rotation speed, measurement error, and pressure drop were validated through experimental measurements performed on a test rig. The role of mechanical friction on the performance of the meter at low flow rates was analyzed and interesting conclusions about its influence on the reduction of the turbine’s rotation speed and on the related change in the measurement error were drawn. The mathematical model developed was capable of reproducing the performance of the meter throughout the majority of the measuring range, and thus was shown to be a very valuable tool for the analysis and improvement of the single-jet water meter studied. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 12 p.[article] Computational modeling and simulation of a single-jet water meter [texte imprimé] / Gorka S. Larraona, Auteur ; Alejandro Rivas, Auteur ; Juan Carlos Ramos, Auteur . - 2009 . - 12 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 12 p.
Mots-clés : Rotation flow (dynamics) turbines errors engineering simulation water meters torque Résumé : A single-jet water meter was modeled and simulated within a wide measuring range that included flow rates in laminar, transitional, and turbulent flow regimes. The interaction between the turbine and the flow, on which the operating principle of this kind of meter is based, was studied in depth from the detailed information provided by simulations of the three dimensional flow within the meter. This interaction was resolved by means of a devised semi-implicit time-marching procedure in such a way that the speed and the position of the turbine were obtained as part of the solution. Results obtained regarding the turbine’s mean rotation speed, measurement error, and pressure drop were validated through experimental measurements performed on a test rig. The role of mechanical friction on the performance of the meter at low flow rates was analyzed and interesting conclusions about its influence on the reduction of the turbine’s rotation speed and on the related change in the measurement error were drawn. The mathematical model developed was capable of reproducing the performance of the meter throughout the majority of the measuring range, and thus was shown to be a very valuable tool for the analysis and improvement of the single-jet water meter studied. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : The effects of splitter plates on turbulent boundary layer on a long flat plate near the trailing edge Type de document : texte imprimé Auteurs : Yoshifumi Jodai, Auteur ; Yoshikazu Takahashi, Auteur ; Masashi Ichimiya, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Boundary layers plates (structures) boundary layer turbulence flat plates pressure flow (dynamics) Résumé : An experimental investigation has been made on a turbulent boundary layer near the trailing edge on a long flat plate. The flow was controlled by an additional splitter plate fitted to the trailing edge along the wake centerline. The length of the splitter plate, l, was varied from a half, to five times the trailing edge thickness, h. Measurements of base pressure behind the trailing edge and of mean velocity and pressure distribution in the turbulent boundary layer on the flat plate were made under the freestream zero-pressure gradient. The absolute value of the base pressure coefficient of the long flat plate was considerably smaller than that of the short flat plate without the splitter plate. A significant increase in the base pressure coefficient was achieved with the splitter plate (l∕h≧1), fitted to the long flat plate. Within an inner layer in the turbulent boundary layer near the trailing edge, the mean velocity increased more than that in the upstream position in the case without the splitter plate. With the splitter plate, however, the base pressure rise made the mean velocity distribution more closely approach that of a fully developed turbulent boundary layer. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.[article] The effects of splitter plates on turbulent boundary layer on a long flat plate near the trailing edge [texte imprimé] / Yoshifumi Jodai, Auteur ; Yoshikazu Takahashi, Auteur ; Masashi Ichimiya, Auteur . - 2009 . - 7 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.
Mots-clés : Boundary layers plates (structures) boundary layer turbulence flat plates pressure flow (dynamics) Résumé : An experimental investigation has been made on a turbulent boundary layer near the trailing edge on a long flat plate. The flow was controlled by an additional splitter plate fitted to the trailing edge along the wake centerline. The length of the splitter plate, l, was varied from a half, to five times the trailing edge thickness, h. Measurements of base pressure behind the trailing edge and of mean velocity and pressure distribution in the turbulent boundary layer on the flat plate were made under the freestream zero-pressure gradient. The absolute value of the base pressure coefficient of the long flat plate was considerably smaller than that of the short flat plate without the splitter plate. A significant increase in the base pressure coefficient was achieved with the splitter plate (l∕h≧1), fitted to the long flat plate. Within an inner layer in the turbulent boundary layer near the trailing edge, the mean velocity increased more than that in the upstream position in the case without the splitter plate. With the splitter plate, however, the base pressure rise made the mean velocity distribution more closely approach that of a fully developed turbulent boundary layer. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Numerical simulation for vortex structure in a turbopump inducer : close relationship with appearance of cavitation instabilities Type de document : texte imprimé Auteurs : Toshiya Kimura, Auteur ; Yoshida, Yoshiki, Auteur ; Tomoyuki Hashimoto, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Cavitation vortices flow (dynamics) gutters blades tunnels computer simulation leakage Résumé : Unsteady cavitation phenomena such as rotating cavitation and cavitation surge are often observed in a turbopump inducer of a rocket engine, sometimes causing undesirable oscillation of the system. Investigation of their mechanism and prediction of such unsteady phenomena are, therefore, crucial in the design of inducers. As many experiments have shown, the appearance of cavitation instability is highly related to the flow rate as well as to the inlet casing geometry. Experimental observations have shown that a very complex flow structure, including such phenomena as backflow and vortices, appears upstream of the inducer. In this work, therefore, we conducted 3D unsteady computational fluid dynamics simulations of noncavitating flow in a turbopump inducer, mainly focusing on the vortex structure, for three types of inlet casing geometry with various flow rates. Simulation results showed that the vortex structure for the geometry of the inlet casing and that for the flow rate differed. Especially, it was found that development of the tip leakage vortex was dependent on the inlet casing geometry and the flow rate. This tendency is analogous to that observed between the appearance of rotating cavitation and the casing geometry and flow rate in cavitation tunnel tests. This result strongly implies that the tip leakage vortex is responsible for the appearance of rotating cavitation. By adding a gutter to the inlet casing, it was found that backflow was completely confined to the gutter regardless of flow rates. This numerical result implies that the volume of cavity generated in the backflow region should be stable despite a change of the flow rate, resulting in the suppression of increase of the mass flow gain factor. This result also supports the experimental result that cavitation surge was effectively suppressed using such a casing with a gutter. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.[article] Numerical simulation for vortex structure in a turbopump inducer : close relationship with appearance of cavitation instabilities [texte imprimé] / Toshiya Kimura, Auteur ; Yoshida, Yoshiki, Auteur ; Tomoyuki Hashimoto, Auteur . - 2009 . - 9 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.
Mots-clés : Cavitation vortices flow (dynamics) gutters blades tunnels computer simulation leakage Résumé : Unsteady cavitation phenomena such as rotating cavitation and cavitation surge are often observed in a turbopump inducer of a rocket engine, sometimes causing undesirable oscillation of the system. Investigation of their mechanism and prediction of such unsteady phenomena are, therefore, crucial in the design of inducers. As many experiments have shown, the appearance of cavitation instability is highly related to the flow rate as well as to the inlet casing geometry. Experimental observations have shown that a very complex flow structure, including such phenomena as backflow and vortices, appears upstream of the inducer. In this work, therefore, we conducted 3D unsteady computational fluid dynamics simulations of noncavitating flow in a turbopump inducer, mainly focusing on the vortex structure, for three types of inlet casing geometry with various flow rates. Simulation results showed that the vortex structure for the geometry of the inlet casing and that for the flow rate differed. Especially, it was found that development of the tip leakage vortex was dependent on the inlet casing geometry and the flow rate. This tendency is analogous to that observed between the appearance of rotating cavitation and the casing geometry and flow rate in cavitation tunnel tests. This result strongly implies that the tip leakage vortex is responsible for the appearance of rotating cavitation. By adding a gutter to the inlet casing, it was found that backflow was completely confined to the gutter regardless of flow rates. This numerical result implies that the volume of cavity generated in the backflow region should be stable despite a change of the flow rate, resulting in the suppression of increase of the mass flow gain factor. This result also supports the experimental result that cavitation surge was effectively suppressed using such a casing with a gutter. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Characterization of air flow through sintered metal foams Type de document : texte imprimé Auteurs : Oliver Reutter, Auteur ; Elena Smirnova, Auteur ; Jörg Sauerhering, Auteur Année de publication : 2009 Article en page(s) : 5 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Density pressure flow (dynamics) permeability measurement air flow metal foams porosity pressure drop foams (chemistry) sintering temperature porous materials gravity (force) Résumé : This study investigates air flow in metallic foams, which are produced by the slip reaction foam sintering (SRFS) process. It was conducted as part of the collaborative research center (SFB) 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants.” The flow through a porous medium is analyzed by Darcy’s equation with the Dupuit/Forchheimer extension. All measurements can be described very well by this equation and permeability and inertial coefficients are obtained for a large quantity of samples with different base materials and different porosities. A threshold porosity of 70% is observed, above which the pressure loss significantly starts sinking with porosity. Additionally, it was found that the permeability was anisotropic. Permeability is lower in the direction of gravity during foaming. Scattering in the data of the permeability and inertial coefficients versus the porosity is observed and discussed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 5 p.[article] Characterization of air flow through sintered metal foams [texte imprimé] / Oliver Reutter, Auteur ; Elena Smirnova, Auteur ; Jörg Sauerhering, Auteur . - 2009 . - 5 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 5 p.
Mots-clés : Density pressure flow (dynamics) permeability measurement air flow metal foams porosity pressure drop foams (chemistry) sintering temperature porous materials gravity (force) Résumé : This study investigates air flow in metallic foams, which are produced by the slip reaction foam sintering (SRFS) process. It was conducted as part of the collaborative research center (SFB) 561 “Thermally Highly Loaded, Porous and Cooled Multi-Layer Systems for Combined Cycle Power Plants.” The flow through a porous medium is analyzed by Darcy’s equation with the Dupuit/Forchheimer extension. All measurements can be described very well by this equation and permeability and inertial coefficients are obtained for a large quantity of samples with different base materials and different porosities. A threshold porosity of 70% is observed, above which the pressure loss significantly starts sinking with porosity. Additionally, it was found that the permeability was anisotropic. Permeability is lower in the direction of gravity during foaming. Scattering in the data of the permeability and inertial coefficients versus the porosity is observed and discussed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Hysteresis curve in reproduction of Reynolds’ color-band experiments Type de document : texte imprimé Auteurs : Hidesada Kanda, Auteur ; Takayuki Yanagiya, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow (dynamics) turbulence pipes water shapes pipe flow valves Reynolds number drops laminar flow Résumé : This article describes the reproduction and extended analysis of Reynolds’ color-band experiment. Reynolds found two critical Reynolds numbers (Rc) in pipe flows: Rc1 of 12,830 from laminar to turbulent flow and Rc2 of 2030 from turbulent to laminar flow. Since no clear relationship has been established between them, we studied how the entrance shape affects Rc. Thus, for the first time, a hysteresis graph can be drawn by connecting the two curves of Rc1 and Rc2 such that the two Rc values lie on separate branches of the hysteresis plot. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 10 p.[article] Hysteresis curve in reproduction of Reynolds’ color-band experiments [texte imprimé] / Hidesada Kanda, Auteur ; Takayuki Yanagiya, Auteur . - 2009 . - 10 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 10 p.
Mots-clés : Flow (dynamics) turbulence pipes water shapes pipe flow valves Reynolds number drops laminar flow Résumé : This article describes the reproduction and extended analysis of Reynolds’ color-band experiment. Reynolds found two critical Reynolds numbers (Rc) in pipe flows: Rc1 of 12,830 from laminar to turbulent flow and Rc2 of 2030 from turbulent to laminar flow. Since no clear relationship has been established between them, we studied how the entrance shape affects Rc. Thus, for the first time, a hysteresis graph can be drawn by connecting the two curves of Rc1 and Rc2 such that the two Rc values lie on separate branches of the hysteresis plot. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Acoustic power calculation in deep cavity flows : a semiempirical approach Type de document : texte imprimé Auteurs : P. Oshkai, Auteur ; T. Yan, Auteur ; A. Velikorodny, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow (dynamics) acoustics bifurcation ducts oscillations Résumé : Acoustic power generated by turbulent flow over a coaxial side branch (deep cavity) resonator mounted in a rectangular duct is calculated using a semiempirical approach. Instantaneous flow velocity is decomposed into an irrotational acoustic component and vorticity-bearing hydrodynamic field. The total velocity at several phases of the acoustic oscillation cycle is measured using digital particle image velocimetry. The acoustic velocity field is numerically calculated. The emphasis is on the effect of the accurate geometry representation for the acoustic field modeling on the calculated acoustic power. Despite the generally low levels of acoustic radiation from the coaxial side branches, when the main duct is incorporated into the model for calculation of the acoustic velocity, the acoustic velocity exhibits substantial horizontal (streamwise) components in the vicinity of the cavity corners. This streamwise acoustic velocity correlates with hydrodynamic horizontal velocity fluctuations, thus contributing to the calculated acoustic power. Spatial structure and strength of the acoustic source change as the distance between the side branches varies. Global quantitative imaging approach is used to characterize the transformation of the acoustic source structure in terms of patterns of instantaneous and phase-averaged flow velocity, vorticity, and streamline topology as well as time-averaged acoustic power. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.[article] Acoustic power calculation in deep cavity flows : a semiempirical approach [texte imprimé] / P. Oshkai, Auteur ; T. Yan, Auteur ; A. Velikorodny, Auteur . - 2009 . - 9 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.
Mots-clés : Flow (dynamics) acoustics bifurcation ducts oscillations Résumé : Acoustic power generated by turbulent flow over a coaxial side branch (deep cavity) resonator mounted in a rectangular duct is calculated using a semiempirical approach. Instantaneous flow velocity is decomposed into an irrotational acoustic component and vorticity-bearing hydrodynamic field. The total velocity at several phases of the acoustic oscillation cycle is measured using digital particle image velocimetry. The acoustic velocity field is numerically calculated. The emphasis is on the effect of the accurate geometry representation for the acoustic field modeling on the calculated acoustic power. Despite the generally low levels of acoustic radiation from the coaxial side branches, when the main duct is incorporated into the model for calculation of the acoustic velocity, the acoustic velocity exhibits substantial horizontal (streamwise) components in the vicinity of the cavity corners. This streamwise acoustic velocity correlates with hydrodynamic horizontal velocity fluctuations, thus contributing to the calculated acoustic power. Spatial structure and strength of the acoustic source change as the distance between the side branches varies. Global quantitative imaging approach is used to characterize the transformation of the acoustic source structure in terms of patterns of instantaneous and phase-averaged flow velocity, vorticity, and streamline topology as well as time-averaged acoustic power. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : A series pressure drop representation for flow through orifice tubes Type de document : texte imprimé Auteurs : T. A. Jankowski, Auteur ; E. N. Schmierer, Auteur ; F. C. Prenger, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow (dynamics) Reynolds number discharge coefficient orifices pressure drop Résumé : A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number. The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.[article] A series pressure drop representation for flow through orifice tubes [texte imprimé] / T. A. Jankowski, Auteur ; E. N. Schmierer, Auteur ; F. C. Prenger, Auteur . - 2009 . - 7 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.
Mots-clés : Flow (dynamics) Reynolds number discharge coefficient orifices pressure drop Résumé : A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number. The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Turbulent boundary layer with negligible wall stress Type de document : texte imprimé Auteurs : Noor Afzal, Auteur Année de publication : 2009 Article en page(s) : 15 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow (dynamics) separation (technology) viscosity stress wakes boundary layer turbulence equations pressure gradient layers composite materials shear (mechanics) Résumé : The turbulent boundary layer subjected to strong adverse pressure gradient near the separation region has been analyzed at large Reynolds numbers by the method of matched asymptotic expansions. The two regions consisting of outer nonlinear wake layer and inner wall layer are analyzed in terms of pressure scaling velocities Up=(νp′∕ρ)1∕3 in the wall region and Uδ=(δp′∕ρ)1∕2 in the outer wake region, where p′ is the streamwise pressure gradient and ρ is the fluid density. In this work, the variables δ, the outer boundary layer thickness, and Uδ, the outer velocity scale, are independent of ν, the molecular kinematic viscosity, which is a better model of fully developed mean turbulent flow. The asymptotic expansions have been matched by Izakson–Millikan–Kolmogorov hypothesis leading to open functional equations. The solution for the velocity distribution gives new composite log-half-power laws, based on the pressure scales, providing a better model of the flow, where the outer composite log-half-power law does not depend on the molecular kinematic viscosity. These new composite laws are better and one may be benefited from their limiting relations that for weak pressure gradient yield the traditional logarithmic laws and for strong adverse pressure gradient yield the half-power laws. During matching of the nonlinear outer layer two cases arise: One where Uδ∕Ue is small and second where Uδ∕Ue of order unity (where Ue is the velocity at the edge of the boundary layer). In the first case, the lowest order nonlinear outer flow under certain conditions shows equilibrium. The outer flow subjected to the constant eddy viscosity closure model is governed by the Falkner–Skan equation subjected to the matching condition of finite slip velocity on the surface. The jet- and wakelike solutions are presented, where the zero velocity slip implying the point of separation, which compares well with Coles traditional wake function. In the second case, higher order terms in the asymptotic solutions for nearly separating flow have been estimated. The proposed composite log-half-power law solution and the limiting half-power law have been well supported by extensive experimental and direct numerical simulation data. For moderate values of the pressure gradient the data show that the proposed composite log-half-power laws are a better model of the flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 15 p.[article] Turbulent boundary layer with negligible wall stress [texte imprimé] / Noor Afzal, Auteur . - 2009 . - 15 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 15 p.
Mots-clés : Flow (dynamics) separation (technology) viscosity stress wakes boundary layer turbulence equations pressure gradient layers composite materials shear (mechanics) Résumé : The turbulent boundary layer subjected to strong adverse pressure gradient near the separation region has been analyzed at large Reynolds numbers by the method of matched asymptotic expansions. The two regions consisting of outer nonlinear wake layer and inner wall layer are analyzed in terms of pressure scaling velocities Up=(νp′∕ρ)1∕3 in the wall region and Uδ=(δp′∕ρ)1∕2 in the outer wake region, where p′ is the streamwise pressure gradient and ρ is the fluid density. In this work, the variables δ, the outer boundary layer thickness, and Uδ, the outer velocity scale, are independent of ν, the molecular kinematic viscosity, which is a better model of fully developed mean turbulent flow. The asymptotic expansions have been matched by Izakson–Millikan–Kolmogorov hypothesis leading to open functional equations. The solution for the velocity distribution gives new composite log-half-power laws, based on the pressure scales, providing a better model of the flow, where the outer composite log-half-power law does not depend on the molecular kinematic viscosity. These new composite laws are better and one may be benefited from their limiting relations that for weak pressure gradient yield the traditional logarithmic laws and for strong adverse pressure gradient yield the half-power laws. During matching of the nonlinear outer layer two cases arise: One where Uδ∕Ue is small and second where Uδ∕Ue of order unity (where Ue is the velocity at the edge of the boundary layer). In the first case, the lowest order nonlinear outer flow under certain conditions shows equilibrium. The outer flow subjected to the constant eddy viscosity closure model is governed by the Falkner–Skan equation subjected to the matching condition of finite slip velocity on the surface. The jet- and wakelike solutions are presented, where the zero velocity slip implying the point of separation, which compares well with Coles traditional wake function. In the second case, higher order terms in the asymptotic solutions for nearly separating flow have been estimated. The proposed composite log-half-power law solution and the limiting half-power law have been well supported by extensive experimental and direct numerical simulation data. For moderate values of the pressure gradient the data show that the proposed composite log-half-power laws are a better model of the flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : A separation criterion with experimental validation for shear-driven films in separated flows Type de document : texte imprimé Auteurs : M. A. Friedrich, Auteur ; H. Lan, Auteur ; J. L. Wegener, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Force flow (dynamics) separation (technology) shear (mechanics) corners (structural elements) liquid films surface tension roughness Résumé : The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.[article] A separation criterion with experimental validation for shear-driven films in separated flows [texte imprimé] / M. A. Friedrich, Auteur ; H. Lan, Auteur ; J. L. Wegener, Auteur . - 2009 . - 9 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 9 p.
Mots-clés : Force flow (dynamics) separation (technology) shear (mechanics) corners (structural elements) liquid films surface tension roughness Résumé : The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : On the interaction of water waves with a surface-parallel vortex Type de document : texte imprimé Auteurs : Amy Warncke Lang, Auteur ; William D. Thacker, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Waves vortices water waves wavelength flow (dynamics) surface waves (fluid) Résumé : An experimental study was performed to investigate the interaction of water waves with a surface-parallel oriented vortex at a free surface. Shadowgraph images were obtained visualizing surface deformations. The role of vortex strength and the direction of approach of the waves were investigated. For favorable waves, with flow velocity at crests parallel to vortex flow, surface deformations were weaker, lasted longer than for a vortex without waves, and were characterized at late times by the appearance of surface-normal vortices. For unfavorable waves incident on the vortex from the other side, surface deformations were stronger and dissipated more quickly. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.[article] On the interaction of water waves with a surface-parallel vortex [texte imprimé] / Amy Warncke Lang, Auteur ; William D. Thacker, Auteur . - 2009 . - 7 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 7 p.
Mots-clés : Waves vortices water waves wavelength flow (dynamics) surface waves (fluid) Résumé : An experimental study was performed to investigate the interaction of water waves with a surface-parallel oriented vortex at a free surface. Shadowgraph images were obtained visualizing surface deformations. The role of vortex strength and the direction of approach of the waves were investigated. For favorable waves, with flow velocity at crests parallel to vortex flow, surface deformations were weaker, lasted longer than for a vortex without waves, and were characterized at late times by the appearance of surface-normal vortices. For unfavorable waves incident on the vortex from the other side, surface deformations were stronger and dissipated more quickly. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : A moving boundary analysis for start-up performance of a nuclear steam generator Type de document : texte imprimé Auteurs : S. Paruya, Auteur ; P. Bhattacharya, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure flow (dynamics) channels (hydraulic engineering) boiling equations steam water nuclear reactor steam generators temperature computation density porosity Résumé : Thermohydraulic phenomena of a steam-water natural-circulation (SWNC) system are very complicated, particularly, during its start-up and shutdown. Its performance strongly depends on the circulation inside it. Accurate quantification of the flow, void fraction, two-phase level, boiling boundary, etc., is difficult at both steady state and transient states like load variation, start-up, and shutdown. Attempts have been made to develop a high-fidelity thermohydraulic model (five-equation scheme) that caters to nonhomogeneous and thermal nonequilibrium flow to derive the dynamic effect of heating rate on the performance of the SWNC loop of steam generator of an Indian nuclear reactor during steaming-up period. The proposed work also attempts to predict boiling height, flow reversal, and density-wave oscillation (DWO). The boiling channel of the SWNC loop is modeled based on the moving boundary analysis using finite volume method. In this moving boundary problem, both control volumes of single-phase zone and two-phase zone change with time. Numerical results have been presented in this paper. The results indicate that both circulation flow variation and two-phase level variation in steam drum have strong dependency on void fraction in the boiling channel. Flow-reversal phenomenon is identified during the initial stage of boiling. Two-phase swelling and collapse that occur during the start-up are predicted. Above a critical heating rate, DWO has been observed. All these phenomena have been explained. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 11 p.[article] A moving boundary analysis for start-up performance of a nuclear steam generator [texte imprimé] / S. Paruya, Auteur ; P. Bhattacharya, Auteur . - 2009 . - 11 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 11 p.
Mots-clés : Pressure flow (dynamics) channels (hydraulic engineering) boiling equations steam water nuclear reactor steam generators temperature computation density porosity Résumé : Thermohydraulic phenomena of a steam-water natural-circulation (SWNC) system are very complicated, particularly, during its start-up and shutdown. Its performance strongly depends on the circulation inside it. Accurate quantification of the flow, void fraction, two-phase level, boiling boundary, etc., is difficult at both steady state and transient states like load variation, start-up, and shutdown. Attempts have been made to develop a high-fidelity thermohydraulic model (five-equation scheme) that caters to nonhomogeneous and thermal nonequilibrium flow to derive the dynamic effect of heating rate on the performance of the SWNC loop of steam generator of an Indian nuclear reactor during steaming-up period. The proposed work also attempts to predict boiling height, flow reversal, and density-wave oscillation (DWO). The boiling channel of the SWNC loop is modeled based on the moving boundary analysis using finite volume method. In this moving boundary problem, both control volumes of single-phase zone and two-phase zone change with time. Numerical results have been presented in this paper. The results indicate that both circulation flow variation and two-phase level variation in steam drum have strong dependency on void fraction in the boiling channel. Flow-reversal phenomenon is identified during the initial stage of boiling. Two-phase swelling and collapse that occur during the start-up are predicted. Above a critical heating rate, DWO has been observed. All these phenomena have been explained. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Design and validation of a scale-adaptive filtering technique for LRN turbulence modeling of unsteady flow Type de document : texte imprimé Auteurs : W. Gyllenram, Auteur ; H. Nilsson, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Turbulence eddies (fluid dynamics) viscosity filters filtration flow (dynamics) modeling Résumé : An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Wilcox’ original low reynolds number k-ω turbulence model. It is shown that the method is suitable for complex industrial unsteady flows in cases where full large eddy simulations (LESs) are unfeasible. During the simulation, the modeled length and time scales are compared to what can potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolvable scales, the resolvable scales will replace the modeled scales in the formulation of the eddy viscosity. The filtered k-ω model is implemented in an in-house computational fluid dynamics (CFD) code, and numerical simulations have been made of strongly swirling flow through a sudden expansion. The new model surpasses the original model in predicting unsteady effects and producing accurate time-averaged results. It is shown to be superior to the wall-adpating local eddy-viscosity (WALE) model on the computational grids considered here, since the turbulence may not be sufficiently resolved for an accurate LES. Because of the adaptive formulation, the filtered k-ω model has the potential to be successfully used in any engineering case where an LES is unfeasible and a Reynolds (ensemble) averaged Navier–Stokes simulation is insufficient. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 10 p.[article] Design and validation of a scale-adaptive filtering technique for LRN turbulence modeling of unsteady flow [texte imprimé] / W. Gyllenram, Auteur ; H. Nilsson, Auteur . - 2009 . - 10 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 10 p.
Mots-clés : Turbulence eddies (fluid dynamics) viscosity filters filtration flow (dynamics) modeling Résumé : An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Wilcox’ original low reynolds number k-ω turbulence model. It is shown that the method is suitable for complex industrial unsteady flows in cases where full large eddy simulations (LESs) are unfeasible. During the simulation, the modeled length and time scales are compared to what can potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolvable scales, the resolvable scales will replace the modeled scales in the formulation of the eddy viscosity. The filtered k-ω model is implemented in an in-house computational fluid dynamics (CFD) code, and numerical simulations have been made of strongly swirling flow through a sudden expansion. The new model surpasses the original model in predicting unsteady effects and producing accurate time-averaged results. It is shown to be superior to the wall-adpating local eddy-viscosity (WALE) model on the computational grids considered here, since the turbulence may not be sufficiently resolved for an accurate LES. Because of the adaptive formulation, the filtered k-ω model has the potential to be successfully used in any engineering case where an LES is unfeasible and a Reynolds (ensemble) averaged Navier–Stokes simulation is insufficient. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Linear stability of weakly forced Taylor-vortex flow Type de document : texte imprimé Auteurs : Roger E. Khayat, Auteur Année de publication : 2009 Article en page(s) : 3 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Stability flow (dynamics) waves vortices cylinders Résumé : Linear stability analysis of fully developed axisymmetric steady spatially modulated Taylor–Couette flow (TCF) is carried out in the narrow-gap limit. In contrast to unforced TCF, only the vortical base flow is possible in the forced case. It is found that the forcing tends to generally destabilize the base flow, especially around the critical point corresponding to unforced flow. Both the critical Taylor number and wave number are found to essentially linearly decrease with modulation amplitude. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 3 p.[article] Linear stability of weakly forced Taylor-vortex flow [texte imprimé] / Roger E. Khayat, Auteur . - 2009 . - 3 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 3 p.
Mots-clés : Stability flow (dynamics) waves vortices cylinders Résumé : Linear stability analysis of fully developed axisymmetric steady spatially modulated Taylor–Couette flow (TCF) is carried out in the narrow-gap limit. In contrast to unforced TCF, only the vortical base flow is possible in the forced case. It is found that the forcing tends to generally destabilize the base flow, especially around the critical point corresponding to unforced flow. Both the critical Taylor number and wave number are found to essentially linearly decrease with modulation amplitude. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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Titre : Fluid flow in an annular microchannel subjected to uniform wall injections Type de document : texte imprimé Auteurs : Mohammad Layeghi, Auteur ; Hamid Reza Seyf, Auteur Année de publication : 2009 Article en page(s) : 5 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Fluid dynamics Reynolds number equations microchannels Navier-Stokes pressure differential equations Résumé : Analytical analysis of fluid flow in an annular microchannel subjected to uniform wall injection at various Reynolds numbers is presented. The classical Navier–Stokes equations are used in the present study. Mathematically, using an appropriate change of variable, Navier–Stokes equations are transformed to a set of nonlinear ordinary differential equations. The governing equations are analytically solved using series solution method. Some analytical results are given for the prediction of velocity profiles and pressure distributions in annular microchannels. The agreement between the computational fluid dynamics and the analytical predictions is very good. However, the analytical results are valid in a limited range of radius ratios and needs more study. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 5 p.[article] Fluid flow in an annular microchannel subjected to uniform wall injections [texte imprimé] / Mohammad Layeghi, Auteur ; Hamid Reza Seyf, Auteur . - 2009 . - 5 p.
Fluids engineering
Langues : Anglais (eng)
in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 5 p.
Mots-clés : Fluid dynamics Reynolds number equations microchannels Navier-Stokes pressure differential equations Résumé : Analytical analysis of fluid flow in an annular microchannel subjected to uniform wall injection at various Reynolds numbers is presented. The classical Navier–Stokes equations are used in the present study. Mathematically, using an appropriate change of variable, Navier–Stokes equations are transformed to a set of nonlinear ordinary differential equations. The governing equations are analytically solved using series solution method. Some analytical results are given for the prediction of velocity profiles and pressure distributions in annular microchannels. The agreement between the computational fluid dynamics and the analytical predictions is very good. However, the analytical results are valid in a limited range of radius ratios and needs more study. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] Exemplaires
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