Dépouillements

Performance and radial loading of a mixed-flow pump under non-uniform suction flow / B. P. M. van Esch in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 7 p. Titre : Performance and radial loading of a mixed-flow pump under non-uniform suction flow Type de document : texte imprimé Auteurs : B. P. M. van Esch, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : nonuniform  suction  velocity  profile;  mixed-flow  pump;  hydrodynamic  forces Résumé : Many centrifugal pumps have a suction velocity profile, which is nonuniform, either by design like in double-suction pumps, sump pumps, and in-line pumps, or as a result of an installation close to an upstream disturbance like a pipe bend. This paper presents an experimental study on the effect of a nonuniform suction velocity profile on performance of a mixed-flow pump and hydrodynamic forces on the impeller. In the experiments, a newly designed dynamometer is used, equipped with six full Wheatstone bridges of strain gauges to measure the six generalized force components. It is placed in between the shaft of the pump and the impeller and corotates with the rotor system. A high accuracy is obtained due to the orthogonality of bridge positioning and the signal conditioning electronics embedded within the dynamometer. The suction flow distribution to the pump is adapted using a pipe bundle situated in the suction pipe. Results of measurements show the influence of the suction flow profile and blade interaction on pump performance and forces. Among the most important observations are a backward whirling motion of the rotor system and a considerable steady radial force. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Performance and radial loading of a mixed-flow pump under non-uniform suction flow [texte imprimé] / B. P. M. van Esch, Auteur . - 2009 . - 7 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 7 p. Mots-clés : nonuniform  suction  velocity  profile;  mixed-flow  pump;  hydrodynamic  forces Résumé : Many centrifugal pumps have a suction velocity profile, which is nonuniform, either by design like in double-suction pumps, sump pumps, and in-line pumps, or as a result of an installation close to an upstream disturbance like a pipe bend. This paper presents an experimental study on the effect of a nonuniform suction velocity profile on performance of a mixed-flow pump and hydrodynamic forces on the impeller. In the experiments, a newly designed dynamometer is used, equipped with six full Wheatstone bridges of strain gauges to measure the six generalized force components. It is placed in between the shaft of the pump and the impeller and corotates with the rotor system. A high accuracy is obtained due to the orthogonality of bridge positioning and the signal conditioning electronics embedded within the dynamometer. The suction flow distribution to the pump is adapted using a pipe bundle situated in the suction pipe. Results of measurements show the influence of the suction flow profile and blade interaction on pump performance and forces. Among the most important observations are a backward whirling motion of the rotor system and a considerable steady radial force. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental and computational study of oscillating turbine cascade and influence of part-span shrouds / Q. X. Huang in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 11 p. Titre : Experimental and computational study of oscillating turbine cascade and influence of part-span shrouds Type de document : texte imprimé Auteurs : Q. X. Huang, Auteur ; L. He, Auteur ; David L. Bell, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : unsteady  flows;  linear  turbine  cascade  oscillating;  part-span  shrouds Résumé : This paper presents a combined experimental and computational study of unsteady flows in a linear turbine cascade oscillating in a three-dimensional bending/flapping mode. Detailed experimental data are obtained on a seven-bladed turbine cascade rig. The middle blade is driven to oscillate and oscillating cascade data are obtained using an influence coefficient method. The numerical simulations are performed by using a 3D nonlinear time-marching Navier–Stokes flow solver. Single-passage domain computations for arbitrary interblade phase angles are achieved by using the Fourier shape correction method. Both measurements and predictions demonstrate a fully 3D behavior of the unsteady flows. The influence of the aerodynamic blockage introduced by part-span shrouds on turbine flutter has been investigated by introducing flat plate shaped shrouds at 75% span. In contrast to practical applications, in the present test configuration, the mode of vibration of the blades remains unchanged by the introduction of the part-span shroud. This allows the influence of the aerodynamic blockage introduced by the part-span shroud to be assessed in isolation from the change in mode shape. A simple shroud model has been developed in the computational solver. The computed unsteady pressures around the shrouds are in good agreement with the experimental data, demonstrating the validity of the simple shroud model. Despite of notable variations in local unsteady pressures around the shrouds, the present results show that the blade aerodynamic damping is largely unaffected by the aerodynamic blockage introduced by part-span shrouds. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental and computational study of oscillating turbine cascade and influence of part-span shrouds [texte imprimé] / Q. X. Huang, Auteur ; L. He, Auteur ; David L. Bell, Auteur . - 2009 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 11 p. Mots-clés : unsteady  flows;  linear  turbine  cascade  oscillating;  part-span  shrouds Résumé : This paper presents a combined experimental and computational study of unsteady flows in a linear turbine cascade oscillating in a three-dimensional bending/flapping mode. Detailed experimental data are obtained on a seven-bladed turbine cascade rig. The middle blade is driven to oscillate and oscillating cascade data are obtained using an influence coefficient method. The numerical simulations are performed by using a 3D nonlinear time-marching Navier–Stokes flow solver. Single-passage domain computations for arbitrary interblade phase angles are achieved by using the Fourier shape correction method. Both measurements and predictions demonstrate a fully 3D behavior of the unsteady flows. The influence of the aerodynamic blockage introduced by part-span shrouds on turbine flutter has been investigated by introducing flat plate shaped shrouds at 75% span. In contrast to practical applications, in the present test configuration, the mode of vibration of the blades remains unchanged by the introduction of the part-span shroud. This allows the influence of the aerodynamic blockage introduced by the part-span shroud to be assessed in isolation from the change in mode shape. A simple shroud model has been developed in the computational solver. The computed unsteady pressures around the shrouds are in good agreement with the experimental data, demonstrating the validity of the simple shroud model. Despite of notable variations in local unsteady pressures around the shrouds, the present results show that the blade aerodynamic damping is largely unaffected by the aerodynamic blockage introduced by part-span shrouds. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental investigation of flow field structure in mixing tee / Seyed Mohammad Hosseini in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 07 p. Titre : Experimental investigation of flow field structure in mixing tee Type de document : texte imprimé Auteurs : Seyed Mohammad Hosseini, Auteur ; Kazuhisa Yuki, Auteur ; Hidetoshi Hashizume, Auteur Année de publication : 2009 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : T-junction;  cooling  system;  turbulent  flow Résumé : T-junction is one of the familiar components in the cooling system of power plants with enormous capability of high-cycle thermal fatigue. This research investigates the structure and mixing mechanism of turbulent flow in a T-junction area with a 90 deg bend upstream. According to the wide distribution of turbulent jets in the T-junction, a re-attached jet was selected previously as the best representative condition with the highest velocity fluctuation and the most complex structure. For considering the mixing mechanism of re-attached jet, T-junction is subdivided into few lateral and longitudinal sections, and each section is visualized separately by particle image velocimetry technique. Corresponding to the experimental data, the branch flow acts as a finite turbulent jet, develops the alternative type of eddies, and causes the high velocity fluctuation near the main pipe wall. Three regions are mainly subject to maximum velocity fluctuation: the region close to the jet boundaries (fluctuation mostly is caused by Kelvin–Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex), and the re-attached area (fluctuation mostly is caused by changing the pressure gradient in the wake area above the jet). Finally, the re-attached area (near the downstream of wake area above the jet) is introduced as a region with strongest possibility to high-cycle thermal fatigue with most effective velocity fluctuation on the main pipe wall above the branch nozzle. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental investigation of flow field structure in mixing tee [texte imprimé] / Seyed Mohammad Hosseini, Auteur ; Kazuhisa Yuki, Auteur ; Hidetoshi Hashizume, Auteur . - 2009 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 07 p. Mots-clés : T-junction;  cooling  system;  turbulent  flow Résumé : T-junction is one of the familiar components in the cooling system of power plants with enormous capability of high-cycle thermal fatigue. This research investigates the structure and mixing mechanism of turbulent flow in a T-junction area with a 90 deg bend upstream. According to the wide distribution of turbulent jets in the T-junction, a re-attached jet was selected previously as the best representative condition with the highest velocity fluctuation and the most complex structure. For considering the mixing mechanism of re-attached jet, T-junction is subdivided into few lateral and longitudinal sections, and each section is visualized separately by particle image velocimetry technique. Corresponding to the experimental data, the branch flow acts as a finite turbulent jet, develops the alternative type of eddies, and causes the high velocity fluctuation near the main pipe wall. Three regions are mainly subject to maximum velocity fluctuation: the region close to the jet boundaries (fluctuation mostly is caused by Kelvin–Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex), and the re-attached area (fluctuation mostly is caused by changing the pressure gradient in the wake area above the jet). Finally, the re-attached area (near the downstream of wake area above the jet) is introduced as a region with strongest possibility to high-cycle thermal fatigue with most effective velocity fluctuation on the main pipe wall above the branch nozzle. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental study of a new flow conditioner on disturbed flow in orifice plate metering / A. Ahmadi in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Titre : Experimental study of a new flow conditioner on disturbed flow in orifice plate metering Type de document : texte imprimé Auteurs : A. Ahmadi, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  conditioner;  mass  flow  rate Résumé : The sensitivity to poor conditioned and swirling flow of flow measurements using an orifice plate are subjects of concern to flowmeter users and manufacturers. Measurements of mass flow rate under different conditions and different Reynolds numbers were used to establish a change in discharge coefficient relative to the standard one. The experimental results show that an optimally shaped flow conditioner could attenuate the effects of both swirl and asymmetrical flows. The optimization of the swirler flow conditioner is a main outcome of this work. So far the experimental results show that the cone swirler flow conditioner is the best one for swirling flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental study of a new flow conditioner on disturbed flow in orifice plate metering [texte imprimé] / A. Ahmadi, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Mots-clés : flow  conditioner;  mass  flow  rate Résumé : The sensitivity to poor conditioned and swirling flow of flow measurements using an orifice plate are subjects of concern to flowmeter users and manufacturers. Measurements of mass flow rate under different conditions and different Reynolds numbers were used to establish a change in discharge coefficient relative to the standard one. The experimental results show that an optimally shaped flow conditioner could attenuate the effects of both swirl and asymmetrical flows. The optimization of the swirler flow conditioner is a main outcome of this work. So far the experimental results show that the cone swirler flow conditioner is the best one for swirling flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

2D Navier–Stokes simulations of microscale viscous pump with slip flow / Khaled M. Bataineh in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 07 p. Titre : 2D Navier–Stokes simulations of microscale viscous pump with slip flow Type de document : texte imprimé Auteurs : Khaled M. Bataineh, Auteur ; Moh’d A. Al-Nimr, Auteur Année de publication : 2009 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Navier–Stokes  equations;  energy  equation;  gaseous  slip  flow;  two-dimensional  microscale  viscous  pumps Résumé : n this paper we provide numerical solution of the Navier–Stokes equations coupled with energy equation for gaseous slip flow in two-dimensional microscale viscous pumps. A first-order slip boundary condition was applied to all internal solid walls. The objectives are to study the performance of the pumps and to study the effect of velocity slip on its performance. Mass flow rate and pump efficiency were calculated for various pump operation conditions when an external pressure load is applied at the pump exit plane. Geometric parameters were held fixed in this work. Microviscous pump performance was studied in detail for several values of the Reynolds number, pressure load, eccentricity, and slip factors. Our numerical results for no-slip were compared with previously published experimental and numerical data and were found to be in very good agreement. Slip values and eccentricity were found to be major parameters that affect the performance of pump. Pump head decreases with increasing slip factors. Maximum pump efficiency increases with increasing slip factor up to Kn approaching 0.1. However, the maximum value of pump efficiency is found to experience a steep degradation for Kn approaching 0.1. The values of moment coefficient always decrease as both slip factor and distance of the rotor from the lower wall increase. Also, as slip factors and distance of the rotor from the lower wall increase, less net flow rate is predicted. For a given fixed driving force at the rotor surface, there is an optimum value for the behavior of pump efficiency with distance of the rotor from the lower wall. Future research should be conducted to modify the current design to make this concept work for higher Knudsen numbers. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] 2D Navier–Stokes simulations of microscale viscous pump with slip flow [texte imprimé] / Khaled M. Bataineh, Auteur ; Moh’d A. Al-Nimr, Auteur . - 2009 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 07 p. Mots-clés : Navier–Stokes  equations;  energy  equation;  gaseous  slip  flow;  two-dimensional  microscale  viscous  pumps Résumé : n this paper we provide numerical solution of the Navier–Stokes equations coupled with energy equation for gaseous slip flow in two-dimensional microscale viscous pumps. A first-order slip boundary condition was applied to all internal solid walls. The objectives are to study the performance of the pumps and to study the effect of velocity slip on its performance. Mass flow rate and pump efficiency were calculated for various pump operation conditions when an external pressure load is applied at the pump exit plane. Geometric parameters were held fixed in this work. Microviscous pump performance was studied in detail for several values of the Reynolds number, pressure load, eccentricity, and slip factors. Our numerical results for no-slip were compared with previously published experimental and numerical data and were found to be in very good agreement. Slip values and eccentricity were found to be major parameters that affect the performance of pump. Pump head decreases with increasing slip factors. Maximum pump efficiency increases with increasing slip factor up to Kn approaching 0.1. However, the maximum value of pump efficiency is found to experience a steep degradation for Kn approaching 0.1. The values of moment coefficient always decrease as both slip factor and distance of the rotor from the lower wall increase. Also, as slip factors and distance of the rotor from the lower wall increase, less net flow rate is predicted. For a given fixed driving force at the rotor surface, there is an optimum value for the behavior of pump efficiency with distance of the rotor from the lower wall. Future research should be conducted to modify the current design to make this concept work for higher Knudsen numbers. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Pre-stall instability distribution over a transonic compressor rotor / A. J. Gannon in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 11 p. Titre : Pre-stall instability distribution over a transonic compressor rotor Type de document : texte imprimé Auteurs : A. J. Gannon, Auteur ; G. V. Hobson, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : transonic  compressor  rotor;  stall Résumé : An investigation of the behavior of a transonic compressor rotor when operating close to stall is presented. The specific areas of interest are the behavior and location of low-frequency instabilities close to stall. In running close to stall, compressors can begin to exhibit nonperiodic flow between the blade passages even when appearing to be operating in a stable steady-state condition. The data from the current rotor clearly show that low-frequency instabilities were present during steady-state operation when stall was approached. These frequencies are not geometrically fixed to the rotor and typically appear at 0.3–0.8 of the rotor speed. The presence of these low-frequency instabilities is known and detection is reasonably commonplace; however, attempts to quantify the location and strength of these instabilities as stall is approached have proved difficult. In the current test fast response pressure sensors were positioned in the case-wall; upstream, downstream, and over the rotor blade tips. Simultaneous data from the sensors were taken at successive steady-state settings with each being closer to stall. A time domain analysis of the data investigates the magnitude of the instabilities and their transient effect on the relative inlet flow angle. The data are also presented in the frequency domain to show the development and distribution of the instabilities over the rotor as stall was approached. Initially the instabilities appeared within the rotor row and extended downstream but at operation closer to stall they began to protrude upstream as well. The greatest amplitude of the instabilities was within the blade row in the complex flow region that contains phenomena such as the tip-vortex/normal-shock interaction and the shock/boundary-layer interaction. In addition as stall is approached the growth of the instabilities is nonlinear and not confined to one frequency. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Pre-stall instability distribution over a transonic compressor rotor [texte imprimé] / A. J. Gannon, Auteur ; G. V. Hobson, Auteur . - 2009 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 11 p. Mots-clés : transonic  compressor  rotor;  stall Résumé : An investigation of the behavior of a transonic compressor rotor when operating close to stall is presented. The specific areas of interest are the behavior and location of low-frequency instabilities close to stall. In running close to stall, compressors can begin to exhibit nonperiodic flow between the blade passages even when appearing to be operating in a stable steady-state condition. The data from the current rotor clearly show that low-frequency instabilities were present during steady-state operation when stall was approached. These frequencies are not geometrically fixed to the rotor and typically appear at 0.3–0.8 of the rotor speed. The presence of these low-frequency instabilities is known and detection is reasonably commonplace; however, attempts to quantify the location and strength of these instabilities as stall is approached have proved difficult. In the current test fast response pressure sensors were positioned in the case-wall; upstream, downstream, and over the rotor blade tips. Simultaneous data from the sensors were taken at successive steady-state settings with each being closer to stall. A time domain analysis of the data investigates the magnitude of the instabilities and their transient effect on the relative inlet flow angle. The data are also presented in the frequency domain to show the development and distribution of the instabilities over the rotor as stall was approached. Initially the instabilities appeared within the rotor row and extended downstream but at operation closer to stall they began to protrude upstream as well. The greatest amplitude of the instabilities was within the blade row in the complex flow region that contains phenomena such as the tip-vortex/normal-shock interaction and the shock/boundary-layer interaction. In addition as stall is approached the growth of the instabilities is nonlinear and not confined to one frequency. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Front condition for gravity currents in channels of nonrectangular symmetric cross-section shapes / B. M. Marino in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 06 p. Titre : Front condition for gravity currents in channels of nonrectangular symmetric cross-section shapes Type de document : texte imprimé Auteurs : B. M. Marino, Auteur ; L. P. Thomas, Auteur Année de publication : 2009 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Froude  number;  gravity  currents;  cross-section  shape;  numerical  model Résumé : We study the variation of the Froude number at the front of gravity currents developed in uniform channels whose cross-section shape depends on a parameter usually used in many numerical and theoretical models. The thickness and front velocity of the dense currents running on the bottom are greater for all the cases studied, resulting in a Froude number greater than that corresponding to the rectangular cross-section shape. The light currents developing along the upper boundary show the opposite trend. It is found that the results are not related to the depth and width of the channel. The relationships obtained agree with the results of laboratory experiments in which open and closed channels of different cross-section shapes are used. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Front condition for gravity currents in channels of nonrectangular symmetric cross-section shapes [texte imprimé] / B. M. Marino, Auteur ; L. P. Thomas, Auteur . - 2009 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 06 p. Mots-clés : Froude  number;  gravity  currents;  cross-section  shape;  numerical  model Résumé : We study the variation of the Froude number at the front of gravity currents developed in uniform channels whose cross-section shape depends on a parameter usually used in many numerical and theoretical models. The thickness and front velocity of the dense currents running on the bottom are greater for all the cases studied, resulting in a Froude number greater than that corresponding to the rectangular cross-section shape. The light currents developing along the upper boundary show the opposite trend. It is found that the results are not related to the depth and width of the channel. The relationships obtained agree with the results of laboratory experiments in which open and closed channels of different cross-section shapes are used. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Vortex dynamics and shedding of a low aspect ratio, flat wing at low Reynolds numbers and high angles of attack / Daniel R. Morse in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 12 p. Titre : Vortex dynamics and shedding of a low aspect ratio, flat wing at low Reynolds numbers and high angles of attack Type de document : texte imprimé Auteurs : Daniel R. Morse, Auteur ; James A. Liburdy, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : vortex  dynamics;  low  Reynolds  number;  low  aspect  ratio;  velocity  fields Résumé : This study focuses on the detection and characterization of vortices in low Reynolds number separated flow over the elliptical leading edge of a low aspect ratio, flat plate wing. Velocity fields were obtained using the time-resolved particle image velocimetry. Experiments were performed on a wing with aspect ratio of 0.5 for velocities of 1.1 m/s, 2.0 m/s, and 5.0 m/s corresponding to chord length Reynolds numbers of 1.47×104, 2.67×104, and 6.67×104, respectively, and angles of attack of 14 deg, 16 deg, 18 deg, and 20 deg. A local swirl calculation was used on proper orthogonal decomposition filtered data for vortex identification and corresponding vortex centers were tracked to determine convective velocities. The swirl function was also analyzed for its temporal frequency response at several discrete points in both the shear layer and in the separated recirculation region. A peak frequency was detected in the shear layer with a corresponding Strouhal number of approximately 3.4 based on the flow direction projected length scale. The Strouhal number increases with both angle of attack and Reynolds number. The shear layer convective length scale, based on the vortex convection velocity, is found to be consistent with the mean separation distance between vortices within the shear layer. This length scale decreases with increasing Rec. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Vortex dynamics and shedding of a low aspect ratio, flat wing at low Reynolds numbers and high angles of attack [texte imprimé] / Daniel R. Morse, Auteur ; James A. Liburdy, Auteur . - 2009 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 12 p. Mots-clés : vortex  dynamics;  low  Reynolds  number;  low  aspect  ratio;  velocity  fields Résumé : This study focuses on the detection and characterization of vortices in low Reynolds number separated flow over the elliptical leading edge of a low aspect ratio, flat plate wing. Velocity fields were obtained using the time-resolved particle image velocimetry. Experiments were performed on a wing with aspect ratio of 0.5 for velocities of 1.1 m/s, 2.0 m/s, and 5.0 m/s corresponding to chord length Reynolds numbers of 1.47×104, 2.67×104, and 6.67×104, respectively, and angles of attack of 14 deg, 16 deg, 18 deg, and 20 deg. A local swirl calculation was used on proper orthogonal decomposition filtered data for vortex identification and corresponding vortex centers were tracked to determine convective velocities. The swirl function was also analyzed for its temporal frequency response at several discrete points in both the shear layer and in the separated recirculation region. A peak frequency was detected in the shear layer with a corresponding Strouhal number of approximately 3.4 based on the flow direction projected length scale. The Strouhal number increases with both angle of attack and Reynolds number. The shear layer convective length scale, based on the vortex convection velocity, is found to be consistent with the mean separation distance between vortices within the shear layer. This length scale decreases with increasing Rec. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Drag reduction in turbulent flow with polymer additives / Yang, Shu-Qing in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Titre : Drag reduction in turbulent flow with polymer additives Type de document : texte imprimé Auteurs : Yang, Shu-Qing, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : turbulent  flows;  velocity  profile;  friction  factor Résumé : The mean velocity profile and friction factor in turbulent flows with polymer additives are investigated using Prandtl’s mixing-length theorem. This study reveals that the mixing-length theorem is valid to express the drag-reducing phenomenon and that the presence of polymer additives increases the damping factor B in van Driest’s model; subsequently reducing the mixing-length, this interprets that the polymer hampers the transfer of turbulent momentum flux, the velocity is increased, and flow drag is reduced. This study also discusses the onset Reynolds number for drag reduction to occur. The predicted velocity, friction factor, and onset Reynolds number are in good agreement with the measured data in the literature. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Drag reduction in turbulent flow with polymer additives [texte imprimé] / Yang, Shu-Qing, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Mots-clés : turbulent  flows;  velocity  profile;  friction  factor Résumé : The mean velocity profile and friction factor in turbulent flows with polymer additives are investigated using Prandtl’s mixing-length theorem. This study reveals that the mixing-length theorem is valid to express the drag-reducing phenomenon and that the presence of polymer additives increases the damping factor B in van Driest’s model; subsequently reducing the mixing-length, this interprets that the polymer hampers the transfer of turbulent momentum flux, the velocity is increased, and flow drag is reduced. This study also discusses the onset Reynolds number for drag reduction to occur. The predicted velocity, friction factor, and onset Reynolds number are in good agreement with the measured data in the literature. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Cavitating turbulent flow simulation in a Francis turbine based on mixture model / Shuhong Liu in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Titre : Cavitating turbulent flow simulation in a Francis turbine based on mixture model Type de document : texte imprimé Auteurs : Shuhong Liu, Auteur ; Liang Zhang, Auteur ; Michihiro Nishi, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Francis  turbine;  cavitation  performance;  mixture  model;  direct  coupling  numerical  technique Résumé : As a numerical method to study the cavitation performance of a Francis turbine, the mixture model for the cavity/liquid two-phase flow is adopted in the cavitating turbulent flow analysis together with the re-normalization group (RNG) k-ε turbulence model in the present paper. The direct coupling numerical technique is used to solve the governing equations of the mixture model for the two-phase flow. Unsteady cavitating flow simulation around a hydrofoil of ALE15 is conducted as preliminary evaluation. Then, the cavitating flow in a Francis turbine is treated from the steady flow simulation since the feasibility of the cavitation model to the performance prediction of the turbine is the present major concern. Comparisons of the computational results with the model test data, i.e., the cavitation characteristics of hydraulic efficiency and the overload vortex rope at the draft tube inlet being reproduced reasonably, indicate that the present method has sufficient potential to simulate the cavitating flow in hydraulic turbines. Further, the unsteady cavitating flow simulation through the Francis turbine is conducted as well to study the pressure fluctuation characters caused by the vortex rope in the draft tube at partial load operation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Cavitating turbulent flow simulation in a Francis turbine based on mixture model [texte imprimé] / Shuhong Liu, Auteur ; Liang Zhang, Auteur ; Michihiro Nishi, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Mots-clés : Francis  turbine;  cavitation  performance;  mixture  model;  direct  coupling  numerical  technique Résumé : As a numerical method to study the cavitation performance of a Francis turbine, the mixture model for the cavity/liquid two-phase flow is adopted in the cavitating turbulent flow analysis together with the re-normalization group (RNG) k-ε turbulence model in the present paper. The direct coupling numerical technique is used to solve the governing equations of the mixture model for the two-phase flow. Unsteady cavitating flow simulation around a hydrofoil of ALE15 is conducted as preliminary evaluation. Then, the cavitating flow in a Francis turbine is treated from the steady flow simulation since the feasibility of the cavitation model to the performance prediction of the turbine is the present major concern. Comparisons of the computational results with the model test data, i.e., the cavitation characteristics of hydraulic efficiency and the overload vortex rope at the draft tube inlet being reproduced reasonably, indicate that the present method has sufficient potential to simulate the cavitating flow in hydraulic turbines. Further, the unsteady cavitating flow simulation through the Francis turbine is conducted as well to study the pressure fluctuation characters caused by the vortex rope in the draft tube at partial load operation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Parallel-plate conductive electrodes for the fabrication of larger 2D colloidal photonic crystals / R. Asmatulu in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 05 p. Titre : Parallel-plate conductive electrodes for the fabrication of larger 2D colloidal photonic crystals Type de document : texte imprimé Auteurs : R. Asmatulu, Auteur ; Kim, S., Auteur ; F. Papadimitrakopoulos, Auteur Année de publication : 2009 Article en page(s) : 05 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : 2D  large  colloidal  photonic  crystals;  parallel-plate  assembly  technique;  gold  electrodes Résumé : A new dielectrophoretic force-induced parallel-plate assembly technique was used to achieve close-packed 2D large colloidal photonic crystals on gold electrodes (∼200 nm thick). The electrodes were patterned on a glass substrate using a conventional UV lithography technique. The experimental tests conducted with 5.3 μm carboxyl functionalized polystyrene particles at various ac and dc voltages, frequencies, and particle concentrations showed that larger size (0.25×3 mm2) colloidal photonic crystals were fabricated on the ground electrode rather than on the working electrode. To date, this is the largest colloidal photonic crystal fabricated using this method. The reason behind this phenomenon can be attributed to the electro-osmotic flow in the colloidal system and dipole-dipole attractions between the colloidal particles. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Parallel-plate conductive electrodes for the fabrication of larger 2D colloidal photonic crystals [texte imprimé] / R. Asmatulu, Auteur ; Kim, S., Auteur ; F. Papadimitrakopoulos, Auteur . - 2009 . - 05 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 05 p. Mots-clés : 2D  large  colloidal  photonic  crystals;  parallel-plate  assembly  technique;  gold  electrodes Résumé : A new dielectrophoretic force-induced parallel-plate assembly technique was used to achieve close-packed 2D large colloidal photonic crystals on gold electrodes (∼200 nm thick). The electrodes were patterned on a glass substrate using a conventional UV lithography technique. The experimental tests conducted with 5.3 μm carboxyl functionalized polystyrene particles at various ac and dc voltages, frequencies, and particle concentrations showed that larger size (0.25×3 mm2) colloidal photonic crystals were fabricated on the ground electrode rather than on the working electrode. To date, this is the largest colloidal photonic crystal fabricated using this method. The reason behind this phenomenon can be attributed to the electro-osmotic flow in the colloidal system and dipole-dipole attractions between the colloidal particles. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Comparison of turbulence modeling strategies for indoor flows / Ammar M. Abdilghanie in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 18 p. Titre : Comparison of turbulence modeling strategies for indoor flows Type de document : texte imprimé Auteurs : Ammar M. Abdilghanie, Auteur ; Lance R. Collins, Auteur ; David A. Caughey, Auteur Année de publication : 2009 Article en page(s) : 18 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence Résumé : Turbulence modeling techniques are compared for the simulation of low speed indoor air flow in a simple room. The effect of inlet turbulence intensity on the flow field is investigated using the constant coefficient large eddy simulation (LES) model with uniform mean inlet conditions at several levels of inlet turbulence intensities. The results show significant differences between the simulations with laminar inflow conditions and those in which turbulence was introduced at the inlet. For simulations with turbulent inlet conditions, it is noticed that the jet transitions to a state of fully developed turbulence wherein the dynamics of the flow become nearly insensitive to any further increase in the level of inlet turbulence. For laminar flow conditions, it is seen that the jet slowly spreads and mixes with the quiescent room air. As a result, the jet reaches a fully developed turbulent state further away from the inlet relative to the simulations with inlet turbulence. The effect of using experimental inlet profiles is also investigated. It is seen that, close to the inlet, the flow is sensitive to the inflow details, whereas further away from the inlet, these effects become less pronounced. The results from the constant coefficient and the dynamic LES models are compared. The most noticeable differences in the flow occur at the locations where the subgrid-scale’s contribution to the turbulent kinetic energy is highest. Finally, the results from the dynamic LES and the k-ϵ models are compared. It is found that there are significant differences between the two models for the zero inlet turbulence limit where the flow is most probably transitional in nature and turbulence has not yet reached a fully developed state. It is seen that in the laminar inflow case the k-ϵ model predicts a fully turbulent jet very close to the inlet and thus fails to capture the slow development of the jet found in LES. Accordingly, the k-ϵ model results are nearly insensitive to the level of inlet turbulence especially far from the origin of the flow. It is also seen that for cases with nonzero inlet turbulence level, the k-ϵ model predicts the general features of the mean flow reasonably well; however, the k-ϵ model overpredicts the jet spreading rate and the turbulent kinetic energy close to the inlet. Furthermore, the k-ϵ model under predicts the turbulence level near the corner of the ceiling as it fails to capture the complicated mean velocity and turbulent kinetic energy, most likely because of the highly intermittent flow pattern found there in LES. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Comparison of turbulence modeling strategies for indoor flows [texte imprimé] / Ammar M. Abdilghanie, Auteur ; Lance R. Collins, Auteur ; David A. Caughey, Auteur . - 2009 . - 18 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 18 p. Mots-clés : flow  (dynamics);  turbulence Résumé : Turbulence modeling techniques are compared for the simulation of low speed indoor air flow in a simple room. The effect of inlet turbulence intensity on the flow field is investigated using the constant coefficient large eddy simulation (LES) model with uniform mean inlet conditions at several levels of inlet turbulence intensities. The results show significant differences between the simulations with laminar inflow conditions and those in which turbulence was introduced at the inlet. For simulations with turbulent inlet conditions, it is noticed that the jet transitions to a state of fully developed turbulence wherein the dynamics of the flow become nearly insensitive to any further increase in the level of inlet turbulence. For laminar flow conditions, it is seen that the jet slowly spreads and mixes with the quiescent room air. As a result, the jet reaches a fully developed turbulent state further away from the inlet relative to the simulations with inlet turbulence. The effect of using experimental inlet profiles is also investigated. It is seen that, close to the inlet, the flow is sensitive to the inflow details, whereas further away from the inlet, these effects become less pronounced. The results from the constant coefficient and the dynamic LES models are compared. The most noticeable differences in the flow occur at the locations where the subgrid-scale’s contribution to the turbulent kinetic energy is highest. Finally, the results from the dynamic LES and the k-ϵ models are compared. It is found that there are significant differences between the two models for the zero inlet turbulence limit where the flow is most probably transitional in nature and turbulence has not yet reached a fully developed state. It is seen that in the laminar inflow case the k-ϵ model predicts a fully turbulent jet very close to the inlet and thus fails to capture the slow development of the jet found in LES. Accordingly, the k-ϵ model results are nearly insensitive to the level of inlet turbulence especially far from the origin of the flow. It is also seen that for cases with nonzero inlet turbulence level, the k-ϵ model predicts the general features of the mean flow reasonably well; however, the k-ϵ model overpredicts the jet spreading rate and the turbulent kinetic energy close to the inlet. Furthermore, the k-ϵ model under predicts the turbulence level near the corner of the ceiling as it fails to capture the complicated mean velocity and turbulent kinetic energy, most likely because of the highly intermittent flow pattern found there in LES. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Unsteady wall shear stress in transient flow using electrochemical method / H. Zidouh in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Titre : Unsteady wall shear stress in transient flow using electrochemical method Type de document : texte imprimé Auteurs : H. Zidouh, Auteur ; Labraga, Larbi, Auteur ; M. William-Louis, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  stress;  shear  (mechanics);  pipes;  valves Résumé : Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Unsteady wall shear stress in transient flow using electrochemical method [texte imprimé] / H. Zidouh, Auteur ; Labraga, Larbi, Auteur ; M. William-Louis, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 08 p. Mots-clés : pressure;  flow  (dynamics);  stress;  shear  (mechanics);  pipes;  valves Résumé : Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re=148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Inviscid flow past two cylinders / R. S. Alassar in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 5 (Mai 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 06 p. Titre : Inviscid flow past two cylinders Type de document : texte imprimé Auteurs : R. S. Alassar, Auteur ; M. A. El-Gebeily, Auteur Année de publication : 2009 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : inviscid  flow  past  two  circular  cylinders Résumé : A simple solution of the problem of inviscid flow past two circular cylinders is presented. The two cylinders may be of different diameters and located at any distance from each other. The solutions of the two main cases, namely, when the flow is perpendicular to the center-to-center line and when the flow is parallel to it (tandem cylinders), lead to a solution of the problem when the flow is in an arbitrary direction. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Inviscid flow past two cylinders [texte imprimé] / R. S. Alassar, Auteur ; M. A. El-Gebeily, Auteur . - 2009 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 5 (Mai 2009) . - 06 p. Mots-clés : inviscid  flow  past  two  circular  cylinders Résumé : A simple solution of the problem of inviscid flow past two circular cylinders is presented. The two cylinders may be of different diameters and located at any distance from each other. The solutions of the two main cases, namely, when the flow is perpendicular to the center-to-center line and when the flow is parallel to it (tandem cylinders), lead to a solution of the problem when the flow is in an arbitrary direction. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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