Dépouillements

Head drop of a spatial turbopump inducer / Nellyana Gonzalo Flores in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 10 p. Titre : Head drop of a spatial turbopump inducer Type de document : texte imprimé Auteurs : Nellyana Gonzalo Flores, Auteur ; Eric Goncalvès, Auteur ; Regiane Fortes Patella, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  cavitation;  drops;  blades;  pressure;  vapors Résumé : A computational fluid dynamics model for cavitation simulation was investigated and compared with experimental results in the case of a three-blade industrial inducer. The model is based on a homogeneous approach of the multiphase flow coupled with a barotropic state law for the cool water vapor/liquid mixture. The numerical results showed a good prediction of the head drop for three flow rates. The hydrodynamic mechanism of the head drop was investigated through a global and local study of the flow fields. The evolution of power, efficiency, and the blade loading during the head drop were analyzed and correlated with the visualizations of the vapor/liquid structures. The local flow analysis was made mainly by studying the relative helicity and the axial velocity fields. A first analysis of numerical results showed the high influence of the cavitation on the backflow structure. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Head drop of a spatial turbopump inducer [texte imprimé] / Nellyana Gonzalo Flores, Auteur ; Eric Goncalvès, Auteur ; Regiane Fortes Patella, Auteur . - 2009 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 10 p. Mots-clés : Flow  (Dynamics);  cavitation;  drops;  blades;  pressure;  vapors Résumé : A computational fluid dynamics model for cavitation simulation was investigated and compared with experimental results in the case of a three-blade industrial inducer. The model is based on a homogeneous approach of the multiphase flow coupled with a barotropic state law for the cool water vapor/liquid mixture. The numerical results showed a good prediction of the head drop for three flow rates. The hydrodynamic mechanism of the head drop was investigated through a global and local study of the flow fields. The evolution of power, efficiency, and the blade loading during the head drop were analyzed and correlated with the visualizations of the vapor/liquid structures. The local flow analysis was made mainly by studying the relative helicity and the axial velocity fields. A first analysis of numerical results showed the high influence of the cavitation on the backflow structure. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Thermodynamic effect on cavitation performances and cavitation instabilities in an inducer / Kengo Kikuta in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Titre : Thermodynamic effect on cavitation performances and cavitation instabilities in an inducer Type de document : texte imprimé Auteurs : Kengo Kikuta, Auteur ; Yoshida, Yoshiki, Auteur ; Mitsuo Watanabe, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Cavitation;  cavities;  nitrogen;  water;  temperature Résumé : Based on the length of the tip cavitation as an indication of cavitation, we focused on the effect of thermodynamics on cavitation performances and cavitation instabilities in an inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) as working fluid with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect on the cavitations. The degree of thermodynamic effect was found to increase with an increase of the cavity length, particularly when the cavity length extended over the throat of the blade passage. In addition, cavitation instabilities occurred both in liquid nitrogen and in cold water when the cavity length increased. Subsynchronous rotating cavitation appeared both in liquid nitrogen and in cold water. In the experiment using liquid nitrogen, the temperature difference between 76K and 80K affected the range in which the subsynchronous rotating cavitation occurred. In contrast, deep cavitation surge appeared only in cold water at lower cavitation numbers. From these experimental results, it was concluded that when the cavity length extends over the throat, the thermodynamic effect also affects the cavitation instabilities as a “thermal damping” through the unsteady cavitation characteristics. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Thermodynamic effect on cavitation performances and cavitation instabilities in an inducer [texte imprimé] / Kengo Kikuta, Auteur ; Yoshida, Yoshiki, Auteur ; Mitsuo Watanabe, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Mots-clés : Cavitation;  cavities;  nitrogen;  water;  temperature Résumé : Based on the length of the tip cavitation as an indication of cavitation, we focused on the effect of thermodynamics on cavitation performances and cavitation instabilities in an inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) as working fluid with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect on the cavitations. The degree of thermodynamic effect was found to increase with an increase of the cavity length, particularly when the cavity length extended over the throat of the blade passage. In addition, cavitation instabilities occurred both in liquid nitrogen and in cold water when the cavity length increased. Subsynchronous rotating cavitation appeared both in liquid nitrogen and in cold water. In the experiment using liquid nitrogen, the temperature difference between 76K and 80K affected the range in which the subsynchronous rotating cavitation occurred. In contrast, deep cavitation surge appeared only in cold water at lower cavitation numbers. From these experimental results, it was concluded that when the cavity length extends over the throat, the thermodynamic effect also affects the cavitation instabilities as a “thermal damping” through the unsteady cavitation characteristics. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

On the preliminary design and noncavitating performance prediction of tapered axial inducers / Luca d’Agostino in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Titre : On the preliminary design and noncavitating performance prediction of tapered axial inducers Type de document : texte imprimé Auteurs : Luca d’Agostino, Auteur ; Lucio Torre, Auteur ; Angelo Pasini, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  blades;  design;  pressure Résumé : A reduced order model for preliminary design and noncavitating performance prediction of tapered axial inducers is illustrated. In the incompressible, inviscid, irrotational flow approximation, the model expresses the 3D flow field in the blade channels by superposing a 2D cross-sectional vorticity correction to a fully guided axisymmetric flow with radially uniform axial velocity. Suitable redefinition of the diffusion factor for bladings with non-negligible radial flow allows for the control of the blade loading and the estimate of the boundary layer blockage at the specified design flow coefficient, providing a simple criterion for matching the hub profile to the axial variation of the blade pitch angle. Carter’s rule is employed to account for flow deviation at the inducer trailing edge. Mass continuity, angular momentum conservation, and Euler’s equation are used to derive a simple second order boundary value problem, whose numerical solution describes the far-field axisymmetric flow at the inducer discharge. A closed form approximate solution is also provided, which proved to yield equivalently accurate results in the prediction of the inducer performance. Finally, the noncavitating pumping characteristic is obtained by introducing suitably adapted correlations of pressure losses and flow deviation effects. The model has been verified to closely approximate the geometry and noncavitating performance of two space inducers tested in Alta’s Cavitating Pump Rotordynamic Test Facility, as well as the measured pumping characteristics of a number of tapered-hub inducers documented in the literature. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] On the preliminary design and noncavitating performance prediction of tapered axial inducers [texte imprimé] / Luca d’Agostino, Auteur ; Lucio Torre, Auteur ; Angelo Pasini, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Mots-clés : Flow  (Dynamics);  blades;  design;  pressure Résumé : A reduced order model for preliminary design and noncavitating performance prediction of tapered axial inducers is illustrated. In the incompressible, inviscid, irrotational flow approximation, the model expresses the 3D flow field in the blade channels by superposing a 2D cross-sectional vorticity correction to a fully guided axisymmetric flow with radially uniform axial velocity. Suitable redefinition of the diffusion factor for bladings with non-negligible radial flow allows for the control of the blade loading and the estimate of the boundary layer blockage at the specified design flow coefficient, providing a simple criterion for matching the hub profile to the axial variation of the blade pitch angle. Carter’s rule is employed to account for flow deviation at the inducer trailing edge. Mass continuity, angular momentum conservation, and Euler’s equation are used to derive a simple second order boundary value problem, whose numerical solution describes the far-field axisymmetric flow at the inducer discharge. A closed form approximate solution is also provided, which proved to yield equivalently accurate results in the prediction of the inducer performance. Finally, the noncavitating pumping characteristic is obtained by introducing suitably adapted correlations of pressure losses and flow deviation effects. The model has been verified to closely approximate the geometry and noncavitating performance of two space inducers tested in Alta’s Cavitating Pump Rotordynamic Test Facility, as well as the measured pumping characteristics of a number of tapered-hub inducers documented in the literature. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Turbulence structure modification and drag reduction by microbubble injections in a Boundary layer channel flow / C. C. Gutiérrez-Torres in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Titre : Turbulence structure modification and drag reduction by microbubble injections in a Boundary layer channel flow Type de document : texte imprimé Auteurs : C. C. Gutiérrez-Torres, Auteur ; Y. A. Hassan, Auteur ; J. A. Jimenez-Bernal, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Microbubbles;  boundary  layers;  channel  flow;  two-phase  flow;  vortices;  drag  reduction;  flow  (Dynamics);  turbulence;  channels  (Hydraulic  engineering);  measurement;  porosity;  stress;  water Résumé : Turbulent boundary layer modification in a channel flow using injection of microbubbles as a means to achieve drag reduction was studied. The physical mechanism of this phenomenon is not yet fully understood. To obtain some information related to this phenomenon, single-phase (pure water) flow and two-phase (water and microbubbles) channel flow measurements are taken. The void fraction conditions were varied while maintaining a Reynolds number of 5128 based on the half channel height. The study indicates that the presence of microbubbles within the boundary layer modifies the turbulence structure such that variations in time and space turbulent scales are observed, as well as ejection and sweep phenomena. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Turbulence structure modification and drag reduction by microbubble injections in a Boundary layer channel flow [texte imprimé] / C. C. Gutiérrez-Torres, Auteur ; Y. A. Hassan, Auteur ; J. A. Jimenez-Bernal, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Mots-clés : Microbubbles;  boundary  layers;  channel  flow;  two-phase  flow;  vortices;  drag  reduction;  flow  (Dynamics);  turbulence;  channels  (Hydraulic  engineering);  measurement;  porosity;  stress;  water Résumé : Turbulent boundary layer modification in a channel flow using injection of microbubbles as a means to achieve drag reduction was studied. The physical mechanism of this phenomenon is not yet fully understood. To obtain some information related to this phenomenon, single-phase (pure water) flow and two-phase (water and microbubbles) channel flow measurements are taken. The void fraction conditions were varied while maintaining a Reynolds number of 5128 based on the half channel height. The study indicates that the presence of microbubbles within the boundary layer modifies the turbulence structure such that variations in time and space turbulent scales are observed, as well as ejection and sweep phenomena. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

PIV study of adverse and favorable pressure gradient turbulent flows over transverse ribs / M. Agelinchaab in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Titre : PIV study of adverse and favorable pressure gradient turbulent flows over transverse ribs Type de document : texte imprimé Auteurs : M. Agelinchaab, Auteur ; Tachie, M. F., Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  turbulence;  boundary  layers;  pressure  gradient;  surface  roughness;  stress;  channels  (Hydraulic  engineering);  cavities Résumé : This paper reports an experimental study of the combined effects of rib roughness and pressure gradient on turbulent flows produced in asymmetric converging and diverging channels. Transverse square ribs with pitch-to-height ratio of 4 were attached to the bottom wall of the channel to produce the rib roughness. A particle image velocimetry technique was used to conduct measurements at several streamwise-transverse planes located upstream, within, and downstream of the converging and diverging sections of the channel. From these measurements, the mean velocities and turbulent statistics at the top plane of the ribs and across the channel were obtained. The data revealed non-negligible wall-normal motion and interaction between the cavities and overlying boundary layers. The different drag characteristics of the rough bottom wall and the smooth top wall produced asymmetric distributions of mean velocity and turbulent statistics across the channel. The asymmetry of these profiles is most extreme in the presence of adverse pressure gradient. Because of the manner in which pressure gradient modifies the mean flow and turbulence production, it was found that the streamwise turbulence intensity and Reynolds shear stress in the vicinity of the ribs are lower in the adverse pressure gradient than in the favorable pressure gradient channel. The results show also that the combined effects of rib roughness and adverse pressure gradient on the turbulent intensity statistics are significantly higher than when roughness and adverse pressure gradient are applied in isolation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] PIV study of adverse and favorable pressure gradient turbulent flows over transverse ribs [texte imprimé] / M. Agelinchaab, Auteur ; Tachie, M. F., Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Mots-clés : Flow  (Dynamics);  turbulence;  boundary  layers;  pressure  gradient;  surface  roughness;  stress;  channels  (Hydraulic  engineering);  cavities Résumé : This paper reports an experimental study of the combined effects of rib roughness and pressure gradient on turbulent flows produced in asymmetric converging and diverging channels. Transverse square ribs with pitch-to-height ratio of 4 were attached to the bottom wall of the channel to produce the rib roughness. A particle image velocimetry technique was used to conduct measurements at several streamwise-transverse planes located upstream, within, and downstream of the converging and diverging sections of the channel. From these measurements, the mean velocities and turbulent statistics at the top plane of the ribs and across the channel were obtained. The data revealed non-negligible wall-normal motion and interaction between the cavities and overlying boundary layers. The different drag characteristics of the rough bottom wall and the smooth top wall produced asymmetric distributions of mean velocity and turbulent statistics across the channel. The asymmetry of these profiles is most extreme in the presence of adverse pressure gradient. Because of the manner in which pressure gradient modifies the mean flow and turbulence production, it was found that the streamwise turbulence intensity and Reynolds shear stress in the vicinity of the ribs are lower in the adverse pressure gradient than in the favorable pressure gradient channel. The results show also that the combined effects of rib roughness and adverse pressure gradient on the turbulent intensity statistics are significantly higher than when roughness and adverse pressure gradient are applied in isolation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Vortex breakdown in an enclosed cylinder with a partially rotating bottom-wall / P. Yu in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Titre : Vortex breakdown in an enclosed cylinder with a partially rotating bottom-wall Type de document : texte imprimé Auteurs : P. Yu, Auteur ; T. S. Lee, Auteur ; Y. Zeng, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Vortices;  cylinders;  angular  momentum;  flow  (Dynamics);  Reynolds  number;  disks Résumé : A numerical study of the axisymmetric flow in a cylindrical chamber of height H is presented, which is driven by a bottom disk rotating at angular velocity Ω. However, unlike most previous studies, the present rotating disk is of smaller radius than the bottom-wall. The boundary curves for the onset of vortex breakdown are presented using different definitions of the nondimensional parameters, depending on whether the cylinder radius R or the disk radius rd is used as the length scale. The study shows that the boundary curves are best correlated when presented in terms of the Reynolds number Ωrd2∕υ, aspect ratio H∕R, and cylinder-to-disk ratio R∕rd. The cylinder-to-disk ratio R∕rd up to 1.6 is found to have noticeable effect on vortex breakdown; this is attributed to the change of effective aspect ratio. The contours of streamline, angular momentum, and azimuthal vorticity are presented and compared with those of whole bottom-wall rotation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Vortex breakdown in an enclosed cylinder with a partially rotating bottom-wall [texte imprimé] / P. Yu, Auteur ; T. S. Lee, Auteur ; Y. Zeng, Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Mots-clés : Vortices;  cylinders;  angular  momentum;  flow  (Dynamics);  Reynolds  number;  disks Résumé : A numerical study of the axisymmetric flow in a cylindrical chamber of height H is presented, which is driven by a bottom disk rotating at angular velocity Ω. However, unlike most previous studies, the present rotating disk is of smaller radius than the bottom-wall. The boundary curves for the onset of vortex breakdown are presented using different definitions of the nondimensional parameters, depending on whether the cylinder radius R or the disk radius rd is used as the length scale. The study shows that the boundary curves are best correlated when presented in terms of the Reynolds number Ωrd2∕υ, aspect ratio H∕R, and cylinder-to-disk ratio R∕rd. The cylinder-to-disk ratio R∕rd up to 1.6 is found to have noticeable effect on vortex breakdown; this is attributed to the change of effective aspect ratio. The contours of streamline, angular momentum, and azimuthal vorticity are presented and compared with those of whole bottom-wall rotation. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

The effect of impeller cutback on the fluid-dynamic pulsations and load at the blade-passing frequency in a centrifugal pump / Raúl Barrio in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 11 p. Titre : The effect of impeller cutback on the fluid-dynamic pulsations and load at the blade-passing frequency in a centrifugal pump Type de document : texte imprimé Auteurs : Raúl Barrio, Auteur ; Blanco, Eduardo, Auteur ; Jorge Parrondo, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure;  flow  (Dynamics);  impellers;  blades;  force;  pumps;  fluctuations  (Physics);  centrifugal  pumps Résumé : A study is presented on the fluid-dynamic pulsations and the corresponding dynamic forces generated in a centrifugal pump with single suction and vaneless volute due to blade-volute interaction. Four impellers with different outlet diameters, obtained from progressive cutbacks (trimmings) of the greatest one, were successively considered in the test pump, so that the radial gap between the impeller and the volute ranged from 8.8% to 23.2% of the impeller radius. The study was based on the numerical computation of the unsteady flow through the machine for a number of flow rates by means of the FLUENT code, solving the 3D unsteady Reynolds-averaged Navier–Stokes equations. Additionally, an experimental series of tests was conducted for the pump with one of the impellers, in order to obtain pressure fluctuation data along the volute front wall that allowed contrasting the numerical predictions. The data collected from the numerical computations were used to estimate the dynamic radial forces and torque at the blade-passing frequency, as a function of flow rate and blade-tongue radial gap. As expected, for a given impeller diameter, the dynamic load increases for off-design conditions, especially for the low range of flow rates, whereas the progressive reduction of the impeller-tongue gap brings about corresponding increments in dynamic load. In particular, varying the blade-tongue gap within the limits of this study resulted in multiplying the maximum magnitude of the blade-passing frequency radial force by a factor of about 4 for low flow rates (i.e., below the nominal flow rate) and 3 for high flow rates. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] The effect of impeller cutback on the fluid-dynamic pulsations and load at the blade-passing frequency in a centrifugal pump [texte imprimé] / Raúl Barrio, Auteur ; Blanco, Eduardo, Auteur ; Jorge Parrondo, Auteur . - 2009 . - 11 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 11 p. Mots-clés : Pressure;  flow  (Dynamics);  impellers;  blades;  force;  pumps;  fluctuations  (Physics);  centrifugal  pumps Résumé : A study is presented on the fluid-dynamic pulsations and the corresponding dynamic forces generated in a centrifugal pump with single suction and vaneless volute due to blade-volute interaction. Four impellers with different outlet diameters, obtained from progressive cutbacks (trimmings) of the greatest one, were successively considered in the test pump, so that the radial gap between the impeller and the volute ranged from 8.8% to 23.2% of the impeller radius. The study was based on the numerical computation of the unsteady flow through the machine for a number of flow rates by means of the FLUENT code, solving the 3D unsteady Reynolds-averaged Navier–Stokes equations. Additionally, an experimental series of tests was conducted for the pump with one of the impellers, in order to obtain pressure fluctuation data along the volute front wall that allowed contrasting the numerical predictions. The data collected from the numerical computations were used to estimate the dynamic radial forces and torque at the blade-passing frequency, as a function of flow rate and blade-tongue radial gap. As expected, for a given impeller diameter, the dynamic load increases for off-design conditions, especially for the low range of flow rates, whereas the progressive reduction of the impeller-tongue gap brings about corresponding increments in dynamic load. In particular, varying the blade-tongue gap within the limits of this study resulted in multiplying the maximum magnitude of the blade-passing frequency radial force by a factor of about 4 for low flow rates (i.e., below the nominal flow rate) and 3 for high flow rates. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Design principles and measured performance of multistage radial flow microturbomachinery at low Reynolds numbers / Changgu Lee in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 11 p. Titre : Design principles and measured performance of multistage radial flow microturbomachinery at low Reynolds numbers Type de document : texte imprimé Auteurs : Changgu Lee, Auteur ; Selin Arslan, Auteur ; Frechette, Luc G., Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure;  flow  (Dynamics);  Reynolds  number;  design;  microturbines;  rotors;  turbines;  blades Résumé : This paper introduces and experimentally demonstrates the design concept of multistage microturbomachinery, which is fabricated using silicon microfabrication technology. The design process for multistage microscale turbomachinery based on meanline analysis is presented, along with computational fluid dynamics predictions of the key aerodynamic performance parameters required in this design process. This modeling was compared with a microturbine device with a 4 mm diameter rotor and 100 μm chord blades, based on microelectromechanical system technology, which was spun to 330,000 rpm and produced 0.38 W of mechanical power. Modeling suggests a turbine adiabatic efficiency of 35% and Re=266 at the maximum speed. The pressure distribution across the blade rows was measured and showed close agreement with the calculation results. Using the model, the microturbine is predicted to produce 3.2 W with an adiabatic efficiency of 63% at a rotor speed of 1.1×106 rpm. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Design principles and measured performance of multistage radial flow microturbomachinery at low Reynolds numbers [texte imprimé] / Changgu Lee, Auteur ; Selin Arslan, Auteur ; Frechette, Luc G., Auteur . - 2009 . - 11 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 11 p. Mots-clés : Pressure;  flow  (Dynamics);  Reynolds  number;  design;  microturbines;  rotors;  turbines;  blades Résumé : This paper introduces and experimentally demonstrates the design concept of multistage microturbomachinery, which is fabricated using silicon microfabrication technology. The design process for multistage microscale turbomachinery based on meanline analysis is presented, along with computational fluid dynamics predictions of the key aerodynamic performance parameters required in this design process. This modeling was compared with a microturbine device with a 4 mm diameter rotor and 100 μm chord blades, based on microelectromechanical system technology, which was spun to 330,000 rpm and produced 0.38 W of mechanical power. Modeling suggests a turbine adiabatic efficiency of 35% and Re=266 at the maximum speed. The pressure distribution across the blade rows was measured and showed close agreement with the calculation results. Using the model, the microturbine is predicted to produce 3.2 W with an adiabatic efficiency of 63% at a rotor speed of 1.1×106 rpm. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

A parametric study of passive flow control for a short, high area ratio 90deg curved diffuser / T. P. Chong in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Titre : A parametric study of passive flow control for a short, high area ratio 90deg curved diffuser Type de document : texte imprimé Auteurs : T. P. Chong, Auteur ; P. F. Joseph, Auteur ; P. O. Davies, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure;  flow  (Dynamics);  diffusers;  vortices;  flow  control;  generators Résumé : This paper represents the results of an experimental program with the aim of controlling the flow in a highly unstable 90deg curved diffuser. The diffuser, which is an integral part of an open jet wind tunnel at the University of Southampton, has the unique configuration of extreme shortness and high area ratio. In this study, several passive flow control devices such as vortex generators, woven wire mesh screens, honeycomb, and guide vanes were employed to control the three-dimensional diffusing flow in a scaled-down model. Although less successful for vortex generators, the other devices were found to improve significantly the uniformity of the flow distribution inside the curved diffuser and hence the exit flow. This study suggests that a cumulative pressure drop coefficient of at least 4.5 at the diffuser exit with at least three guide vanes is required to achieve adequate flow uniformity at the diffuser exit. These flow conditioning treatments were applied to the full-scale diffuser with exit dimensions of 1.3×1.3m2. Flow with comparable uniformity to the scale-model diffuser is obtained. This study provides valuable guidelines on the design of curved/straight diffusers with nonseparated flow and minimal pressure distortion at the exit. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] A parametric study of passive flow control for a short, high area ratio 90deg curved diffuser [texte imprimé] / T. P. Chong, Auteur ; P. F. Joseph, Auteur ; P. O. Davies, Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 12 p. Mots-clés : Pressure;  flow  (Dynamics);  diffusers;  vortices;  flow  control;  generators Résumé : This paper represents the results of an experimental program with the aim of controlling the flow in a highly unstable 90deg curved diffuser. The diffuser, which is an integral part of an open jet wind tunnel at the University of Southampton, has the unique configuration of extreme shortness and high area ratio. In this study, several passive flow control devices such as vortex generators, woven wire mesh screens, honeycomb, and guide vanes were employed to control the three-dimensional diffusing flow in a scaled-down model. Although less successful for vortex generators, the other devices were found to improve significantly the uniformity of the flow distribution inside the curved diffuser and hence the exit flow. This study suggests that a cumulative pressure drop coefficient of at least 4.5 at the diffuser exit with at least three guide vanes is required to achieve adequate flow uniformity at the diffuser exit. These flow conditioning treatments were applied to the full-scale diffuser with exit dimensions of 1.3×1.3m2. Flow with comparable uniformity to the scale-model diffuser is obtained. This study provides valuable guidelines on the design of curved/straight diffusers with nonseparated flow and minimal pressure distortion at the exit. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Strategies for simulating flow through low-pressure turbine cascade / Andreas Gross in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 13 p. Titre : Strategies for simulating flow through low-pressure turbine cascade Type de document : texte imprimé Auteurs : Andreas Gross, Auteur ; Hermann F. Fasel, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pressure;  flow  (Dynamics);  separation  (Technology);  turbulence;  engineering  simulation;  blades;  Reynolds-averaged  Navier–Stokes  equations;  Reynolds  number;  cascades  (Fluid  dynamics);  turbines Résumé : Laminar separation on the suction side of low-pressure turbine blades at low Reynolds number operating conditions deteriorates overall engine performance and has to be avoided. This requirement affects the blade design and poses a limitation on the maximum permissible blade spacing. Better understanding of the flow physics associated with laminar separation will aid in the development of flow control techniques for delaying or preventing flow separation. Simulations of low-pressure turbine flows are challenging as both unsteady separation and transition are present and interacting. Available simulation strategies have to be evaluated before a well-founded decision for the choice of a particular simulation strategy can be made. With this in mind, this paper provides a comparison of different flow simulation strategies: In particular, “coarse grid” direct numerical simulations, implicit large-eddy simulations, and simulations based on a hybrid turbulence modeling approach are evaluated with particular emphasis on investigating the dynamics of the coherent structures that are generated in the separated flow region and that appear to dominate the entire flow. It is shown that in some instances, the effect of the dominant coherent structures can also be predicted by unsteady Reynolds-averaged Navier–Stokes calculations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Strategies for simulating flow through low-pressure turbine cascade [texte imprimé] / Andreas Gross, Auteur ; Hermann F. Fasel, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 13 p. Mots-clés : Pressure;  flow  (Dynamics);  separation  (Technology);  turbulence;  engineering  simulation;  blades;  Reynolds-averaged  Navier–Stokes  equations;  Reynolds  number;  cascades  (Fluid  dynamics);  turbines Résumé : Laminar separation on the suction side of low-pressure turbine blades at low Reynolds number operating conditions deteriorates overall engine performance and has to be avoided. This requirement affects the blade design and poses a limitation on the maximum permissible blade spacing. Better understanding of the flow physics associated with laminar separation will aid in the development of flow control techniques for delaying or preventing flow separation. Simulations of low-pressure turbine flows are challenging as both unsteady separation and transition are present and interacting. Available simulation strategies have to be evaluated before a well-founded decision for the choice of a particular simulation strategy can be made. With this in mind, this paper provides a comparison of different flow simulation strategies: In particular, “coarse grid” direct numerical simulations, implicit large-eddy simulations, and simulations based on a hybrid turbulence modeling approach are evaluated with particular emphasis on investigating the dynamics of the coherent structures that are generated in the separated flow region and that appear to dominate the entire flow. It is shown that in some instances, the effect of the dominant coherent structures can also be predicted by unsteady Reynolds-averaged Navier–Stokes calculations. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Laminar non-newtonian fluid flow in noncircular ducts and microchannels / Y. S. Muzychka in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 7 p. Titre : Laminar non-newtonian fluid flow in noncircular ducts and microchannels Type de document : texte imprimé Auteurs : Y. S. Muzychka, Auteur ; J. Edge, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  ducts;  shapes;  icrochannels;  non-Newtonian  fluids;  equations;  fluids;  shear  (Mechanics);  channels  (Hydraulic  engineering) Résumé : Non-Newtonian fluid flow in noncircular ducts and microchannels is examined. A simple model is proposed for power law fluids based on the Rabinowitsch–Mooney formulation. By means of a new characteristic length scale, the square root of the cross-sectional area, it is shown that dimensionless wall shear stress can be made a weak function of duct shape. The proposed model is based on the solution for the rectangular duct and has an accuracy of ±10% or better. The current model eliminates the need for tabulated data or equations for several common shapes found in handbooks, namely, circular tube, elliptic tube, parallel channel, rectangular duct, isosceles triangular duct, circular annulus, and polygonal ducts. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Laminar non-newtonian fluid flow in noncircular ducts and microchannels [texte imprimé] / Y. S. Muzychka, Auteur ; J. Edge, Auteur . - 2009 . - 7 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 7 p. Mots-clés : Flow  (Dynamics);  ducts;  shapes;  icrochannels;  non-Newtonian  fluids;  equations;  fluids;  shear  (Mechanics);  channels  (Hydraulic  engineering) Résumé : Non-Newtonian fluid flow in noncircular ducts and microchannels is examined. A simple model is proposed for power law fluids based on the Rabinowitsch–Mooney formulation. By means of a new characteristic length scale, the square root of the cross-sectional area, it is shown that dimensionless wall shear stress can be made a weak function of duct shape. The proposed model is based on the solution for the rectangular duct and has an accuracy of ±10% or better. The current model eliminates the need for tabulated data or equations for several common shapes found in handbooks, namely, circular tube, elliptic tube, parallel channel, rectangular duct, isosceles triangular duct, circular annulus, and polygonal ducts. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Optical diffusometry techniques and applications in biological agent detection / Aloke Kumar in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 11 (Novembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Titre : Optical diffusometry techniques and applications in biological agent detection Type de document : texte imprimé Auteurs : Aloke Kumar, Auteur ; Venu M. Gorti, Auteur ; Hao Shang, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Diffusion  (Physics);  particulate  matter;  biological  agents Résumé : Optical diffusometry is a technique used for measuring diffusion. This work explores the possibility of directly measuring diffusion coefficients of submicron particles for pathogen detection. The diffusion coefficient of these particles is a function of the drag coefficient of the particle at constant temperatures. Particles introduced into a sample containing an analyte bind with the analyte if functionalized with the appropriate antibodies. This leads to an increase in the hydrodynamic drag of the particles and hence a decrease in their diffusion coefficient. This study uses the above principle to effectively measure the diffusion coefficient of the particles using two different experimental approaches. The measured reduction in the diffusion coefficient can be correlated to the amount of analyte present and thus forms the basis of biological agent detection. Sensitivity to experimental conditions is analyzed. It is observed that alternative techniques such as optical trapping hold promise: the diffusive behavior of particles in optical traps is found to be quantitatively different from that of a free particle. Hence preconditions are identified to make optical trapping appropriate for agent detection. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Optical diffusometry techniques and applications in biological agent detection [texte imprimé] / Aloke Kumar, Auteur ; Venu M. Gorti, Auteur ; Hao Shang, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 11 (Novembre 2008) . - 8 p. Mots-clés : Diffusion  (Physics);  particulate  matter;  biological  agents Résumé : Optical diffusometry is a technique used for measuring diffusion. This work explores the possibility of directly measuring diffusion coefficients of submicron particles for pathogen detection. The diffusion coefficient of these particles is a function of the drag coefficient of the particle at constant temperatures. Particles introduced into a sample containing an analyte bind with the analyte if functionalized with the appropriate antibodies. This leads to an increase in the hydrodynamic drag of the particles and hence a decrease in their diffusion coefficient. This study uses the above principle to effectively measure the diffusion coefficient of the particles using two different experimental approaches. The measured reduction in the diffusion coefficient can be correlated to the amount of analyte present and thus forms the basis of biological agent detection. Sensitivity to experimental conditions is analyzed. It is observed that alternative techniques such as optical trapping hold promise: the diffusive behavior of particles in optical traps is found to be quantitatively different from that of a free particle. Hence preconditions are identified to make optical trapping appropriate for agent detection. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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