Dépouillements

Performance improvement of weis-fogh type ship’s propulsion mechanism using a wing restrained by an elastic spring / Kideok Ro in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 06 p. Titre : Performance improvement of weis-fogh type ship’s propulsion mechanism using a wing restrained by an elastic spring Type de document : texte imprimé Auteurs : Kideok Ro, Auteur Année de publication : 2010 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : drag  (fluid  dynamics);  thrust;  propulsion;  engineering  prototypes;  springs;  wings;  mechanisms Résumé : This study was conducted in an attempt to improve the hydrodynamic performance of a Weis-Fogh type ship propulsion mechanism by installing a spring to the wing so that the opening angle of the wing can be changed automatically. With the prototype design, the average thrust coefficient was almost fixed with all velocity ratios; but with the spring type, the thrust coefficient was increased sharply as the velocity ratio increased. The average propulsive efficiency was higher with a bigger opening angle in the prototype but in the spring type design, the one with a smaller spring coefficient had higher efficiency. In the case of velocity ratios over 1.5 where big thrust can be generated, the spring type had more than twice the increase in propulsion efficiency compared with the prototype. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Performance improvement of weis-fogh type ship’s propulsion mechanism using a wing restrained by an elastic spring [texte imprimé] / Kideok Ro, Auteur . - 2010 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 06 p. Mots-clés : drag  (fluid  dynamics);  thrust;  propulsion;  engineering  prototypes;  springs;  wings;  mechanisms Résumé : This study was conducted in an attempt to improve the hydrodynamic performance of a Weis-Fogh type ship propulsion mechanism by installing a spring to the wing so that the opening angle of the wing can be changed automatically. With the prototype design, the average thrust coefficient was almost fixed with all velocity ratios; but with the spring type, the thrust coefficient was increased sharply as the velocity ratio increased. The average propulsive efficiency was higher with a bigger opening angle in the prototype but in the spring type design, the one with a smaller spring coefficient had higher efficiency. In the case of velocity ratios over 1.5 where big thrust can be generated, the spring type had more than twice the increase in propulsion efficiency compared with the prototype. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry / Tariq Ahmad in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 13 p. Titre : Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry Type de document : texte imprimé Auteurs : Tariq Ahmad, Auteur ; Ibrahim Hassan, Auteur Année de publication : 2010 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  particulate  matter;  reservoirs;  Reynolds  number;  entrance  region;  experiment  analysis;  microchannels;  microparticles;  mechanisms Résumé : The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental analysis of microchannel entrance length characteristics using microparticle image velocimetry [texte imprimé] / Tariq Ahmad, Auteur ; Ibrahim Hassan, Auteur . - 2010 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 13 p. Mots-clés : flow  (dynamics);  channels  (hydraulic  engineering);  particulate  matter;  reservoirs;  Reynolds  number;  entrance  region;  experiment  analysis;  microchannels;  microparticles;  mechanisms Résumé : The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Combined effect of surface roughness and heterogeneity of wall potential on electroosmosis in microfluidic/nanofuidic channels / S. Bhattacharyya in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 11 p. Titre : Combined effect of surface roughness and heterogeneity of wall potential on electroosmosis in microfluidic/nanofuidic channels Type de document : texte imprimé Auteurs : S. Bhattacharyya, Auteur ; A. K. Nayak, Auteur Année de publication : 2010 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  electric  fields;  ions;  channels  (hydraulic  engineering);  surface  roughness;  electroosmosis;  vortices;  equations Résumé : The motivation of the present study is to generate vortical flow by introducing channel wall roughness in the form of a wall mounted block that has a step-jump in ζ-potential on the upper face. The characteristics for the electrokinetic flow are obtained by numerically solving the Poisson equation, the Nernst–Planck equation, and the Navier–Stokes equations, simultaneously. A numerical method based on the pressure correction iterative algorithm (SIMPLE ) is adopted to compute the flow field and mole fraction of the ions. The potential patch induces a strong recirculation vortex, which in turn generates a strong pressure gradient. The strength of the vortex, which appears adjacent to the potential patch, increases almost linearly with the increase in ζ-potential. The streamlines follow a tortuous path near the wall roughness. The average axial flow rate over the block is enhanced significantly. We found that the ionic distribution follow the equilibrium Boltzmann distribution away from the wall roughness. The solutions based on the Poisson–Boltzmann distribution and the Nernst–Planck model are different when the inertial effect is significant. The combined effects due to geometrical modulation of the channel wall and heterogeneity in ζ-potential is found to produce a stronger vortex, and hence a stronger mixing, compared with either of these. Increase in ζ-potential increases both the transport rate and mixing efficiency. A novelty of the present configuration is that the vortex forms above the obstacle even when the patch potential is negative. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Combined effect of surface roughness and heterogeneity of wall potential on electroosmosis in microfluidic/nanofuidic channels [texte imprimé] / S. Bhattacharyya, Auteur ; A. K. Nayak, Auteur . - 2010 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 11 p. Mots-clés : flow  (dynamics);  electric  fields;  ions;  channels  (hydraulic  engineering);  surface  roughness;  electroosmosis;  vortices;  equations Résumé : The motivation of the present study is to generate vortical flow by introducing channel wall roughness in the form of a wall mounted block that has a step-jump in ζ-potential on the upper face. The characteristics for the electrokinetic flow are obtained by numerically solving the Poisson equation, the Nernst–Planck equation, and the Navier–Stokes equations, simultaneously. A numerical method based on the pressure correction iterative algorithm (SIMPLE ) is adopted to compute the flow field and mole fraction of the ions. The potential patch induces a strong recirculation vortex, which in turn generates a strong pressure gradient. The strength of the vortex, which appears adjacent to the potential patch, increases almost linearly with the increase in ζ-potential. The streamlines follow a tortuous path near the wall roughness. The average axial flow rate over the block is enhanced significantly. We found that the ionic distribution follow the equilibrium Boltzmann distribution away from the wall roughness. The solutions based on the Poisson–Boltzmann distribution and the Nernst–Planck model are different when the inertial effect is significant. The combined effects due to geometrical modulation of the channel wall and heterogeneity in ζ-potential is found to produce a stronger vortex, and hence a stronger mixing, compared with either of these. Increase in ζ-potential increases both the transport rate and mixing efficiency. A novelty of the present configuration is that the vortex forms above the obstacle even when the patch potential is negative. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Application of realizability and shock unsteadiness to k−ε simulations of under-expanded axisymmetric supersonic free jets / Babak Emami in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 07 p. Titre : Application of realizability and shock unsteadiness to k−ε simulations of under-expanded axisymmetric supersonic free jets Type de document : texte imprimé Auteurs : Babak Emami, Auteur ; Markus Bussmann, Auteur ; Honghi Tran, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : compressibility;  mach  number;  turbulence;  eddies  (fluid  dynamics);  viscosity;  shock  waves;  jets;  shock  (mechanics);  engineering  simulation;  equations Résumé : An explicit cell-centered finite volume solver coupled to a k−ε turbulence model corrected for structural compressibility fails to satisfactorily predict the behavior of under-expanded supersonic jets exhausting into still air, because the model does not properly account for the turbulence/shock wave interaction. Two approaches are examined: imposing a realizability constraint and taking into account shock unsteadiness effects. Although both corrections yield better agreement with experimental data of under-expanded jets, the realizability constraint yields better results than the shock unsteadiness correction. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Application of realizability and shock unsteadiness to k−ε simulations of under-expanded axisymmetric supersonic free jets [texte imprimé] / Babak Emami, Auteur ; Markus Bussmann, Auteur ; Honghi Tran, Auteur . - 2010 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 07 p. Mots-clés : compressibility;  mach  number;  turbulence;  eddies  (fluid  dynamics);  viscosity;  shock  waves;  jets;  shock  (mechanics);  engineering  simulation;  equations Résumé : An explicit cell-centered finite volume solver coupled to a k−ε turbulence model corrected for structural compressibility fails to satisfactorily predict the behavior of under-expanded supersonic jets exhausting into still air, because the model does not properly account for the turbulence/shock wave interaction. Two approaches are examined: imposing a realizability constraint and taking into account shock unsteadiness effects. Although both corrections yield better agreement with experimental data of under-expanded jets, the realizability constraint yields better results than the shock unsteadiness correction. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Analysis of unsteady confined viscous flows with variable inflow velocity and oscillating walls / Dan Mateescu in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 09 p. Titre : Analysis of unsteady confined viscous flows with variable inflow velocity and oscillating walls Type de document : texte imprimé Auteurs : Dan Mateescu, Auteur ; Manuel Muñoz, Auteur ; Olivier Scholz, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : oscillations;  flow  (dynamics);  separation  (technology);  Reynolds  number;  foundry  coatings;  fluctuations  (physics);  confined  flow;  cycles;  equations;  unsteady  flow;  inflow Résumé : The inflow velocities in various components of many engineering systems often display variations in time (fluctuations) during the operation cycle, which may substantially affect the flow-induced vibrations and instabilities of these systems. For this reason, the aeroelasticity study of these systems should include the effect of the inflow velocity variations, which until now has not been taken into account. This paper presents a fluid-dynamic analysis of the unsteady confined viscous flows generated by the variations in time of the inflow velocities and by oscillating walls, which is required for the study of flow-induced vibration and instability of various engineering systems. The time-accurate solutions of the Navier–Stokes equations for these unsteady flows are obtained with a finite-difference method using artificial compressibility on a stretched staggered grid, which is a second-order method in space and time. A special decoupling procedure, based on the utilization of the continuity equation, is used in conjunction with a factored alternate direction scheme to substantially enhance the computational efficiency of the method by reducing the problem to the solution of scalar tridiagonal systems of equations. This method is applied to obtain solutions for the benchmark unsteady confined flow past a downstream-facing step, generated by harmonic variations in time of the inflow velocity and by an oscillating wall, which display multiple flow separation regions on the upper and lower walls. The influence of the Reynolds number and of the oscillation frequency and the amplitudes of the inflow velocity and oscillating wall on the formation of the flow separation regions are thoroughly analyzed in this paper. It was found that for certain values of the Reynolds number and oscillation frequency and amplitudes, the flow separation at the upper wall is present only during a portion of the oscillatory cycle and disappears for the rest of the cycle, and that for other values of these parameters secondary flow separations may also be formed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Analysis of unsteady confined viscous flows with variable inflow velocity and oscillating walls [texte imprimé] / Dan Mateescu, Auteur ; Manuel Muñoz, Auteur ; Olivier Scholz, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 09 p. Mots-clés : oscillations;  flow  (dynamics);  separation  (technology);  Reynolds  number;  foundry  coatings;  fluctuations  (physics);  confined  flow;  cycles;  equations;  unsteady  flow;  inflow Résumé : The inflow velocities in various components of many engineering systems often display variations in time (fluctuations) during the operation cycle, which may substantially affect the flow-induced vibrations and instabilities of these systems. For this reason, the aeroelasticity study of these systems should include the effect of the inflow velocity variations, which until now has not been taken into account. This paper presents a fluid-dynamic analysis of the unsteady confined viscous flows generated by the variations in time of the inflow velocities and by oscillating walls, which is required for the study of flow-induced vibration and instability of various engineering systems. The time-accurate solutions of the Navier–Stokes equations for these unsteady flows are obtained with a finite-difference method using artificial compressibility on a stretched staggered grid, which is a second-order method in space and time. A special decoupling procedure, based on the utilization of the continuity equation, is used in conjunction with a factored alternate direction scheme to substantially enhance the computational efficiency of the method by reducing the problem to the solution of scalar tridiagonal systems of equations. This method is applied to obtain solutions for the benchmark unsteady confined flow past a downstream-facing step, generated by harmonic variations in time of the inflow velocity and by an oscillating wall, which display multiple flow separation regions on the upper and lower walls. The influence of the Reynolds number and of the oscillation frequency and the amplitudes of the inflow velocity and oscillating wall on the formation of the flow separation regions are thoroughly analyzed in this paper. It was found that for certain values of the Reynolds number and oscillation frequency and amplitudes, the flow separation at the upper wall is present only during a portion of the oscillatory cycle and disappears for the rest of the cycle, and that for other values of these parameters secondary flow separations may also be formed. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Eddy heat transfer by secondary görtler instability / L. Momayez in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Titre : Eddy heat transfer by secondary görtler instability Type de document : texte imprimé Auteurs : L. Momayez, Auteur ; G. Delacourt, Auteur ; P. Dupont, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  heat  transfer;  turbulence;  eddies  (fluid  dynamics);  boundary  layers;  vortices Résumé : Experimental measurements of flow and heat transfer in a concave surface boundary layer in the presence of streamwise counter-rotating Görtler vortices show conclusively that local surface heat-transfer rates can exceed that of the turbulent flat-plate boundary layer even in the absence of turbulence. We have observed unexpected heat-transfer behavior in a laminar boundary layer on a concave wall even at low nominal velocity, a configuration not studied in the literature: The heat-transfer enhancement is extremely high, well above that corresponding to a turbulent boundary layer on a flat plate. To quantify the effect of freestream velocity on heat-transfer intensification, two criteria are defined for the growth of the Görtler instability: Pz for primary instability and Prms for the secondary instability. The evolution of these criteria along the concave surface boundary layer clearly shows that the secondary instability grows faster than the primary instability. Measurements show that beyond a certain distance the heat-transfer enhancement is basically correlated with Prms, so that the high heat-transfer intensification at low freestream velocities is due to the high growth rate of the secondary instability. The relative heat-transfer enhancement seems to be independent of the nominal velocity (global Reynolds number) and allows predicting the influence of the Görtler instabilities in a large variety of situations. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Eddy heat transfer by secondary görtler instability [texte imprimé] / L. Momayez, Auteur ; G. Delacourt, Auteur ; P. Dupont, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Mots-clés : flow  (dynamics);  heat  transfer;  turbulence;  eddies  (fluid  dynamics);  boundary  layers;  vortices Résumé : Experimental measurements of flow and heat transfer in a concave surface boundary layer in the presence of streamwise counter-rotating Görtler vortices show conclusively that local surface heat-transfer rates can exceed that of the turbulent flat-plate boundary layer even in the absence of turbulence. We have observed unexpected heat-transfer behavior in a laminar boundary layer on a concave wall even at low nominal velocity, a configuration not studied in the literature: The heat-transfer enhancement is extremely high, well above that corresponding to a turbulent boundary layer on a flat plate. To quantify the effect of freestream velocity on heat-transfer intensification, two criteria are defined for the growth of the Görtler instability: Pz for primary instability and Prms for the secondary instability. The evolution of these criteria along the concave surface boundary layer clearly shows that the secondary instability grows faster than the primary instability. Measurements show that beyond a certain distance the heat-transfer enhancement is basically correlated with Prms, so that the high heat-transfer intensification at low freestream velocities is due to the high growth rate of the secondary instability. The relative heat-transfer enhancement seems to be independent of the nominal velocity (global Reynolds number) and allows predicting the influence of the Görtler instabilities in a large variety of situations. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

On self-similarity in the inner wall layer of a turbulent channel flow / Bérengère Podvin in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 15 p. Titre : On self-similarity in the inner wall layer of a turbulent channel flow Type de document : texte imprimé Auteurs : Bérengère Podvin, Auteur ; Yann Fraigneau, Auteur ; Julien Jouanguy, Auteur Année de publication : 2010 Article en page(s) : 15 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence;  eddies  (fluid  dynamics);  computer  simulation;  Reynolds  number;  polishing  equipment;  eigenfunctions;  channel  flow Résumé : We use proper orthogonal decomposition (POD) to estimate the flow in the near-wall region based on information from the outer buffer layer. Our goal is to assess how the flow structures in the inner wall region are connected to those further away from the wall, and to investigate the nature of the coupling between the inner and the outer region in the POD framework. Reconstructions are carried out for numerical simulations of a plane channel flow at two different Reynolds numbers. We show that elongated structures with a spanwise wavelength smaller than a critical value tend to be concentrated in the inner layer. The critical wavelength is shown to scale with the inner layer height, and interactions between the inner and the outer layer appear to take place predominantly over a self-similar, height-dependent, range of wavenumbers, in agreement with Townsend’s attached eddy hypothesis. The reconstructed field appears to capture an adequate energy content and to remain correlated with the real field even close to the wall, which reflects the persistence of energetic structures over the extent of the buffer layer. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] On self-similarity in the inner wall layer of a turbulent channel flow [texte imprimé] / Bérengère Podvin, Auteur ; Yann Fraigneau, Auteur ; Julien Jouanguy, Auteur . - 2010 . - 15 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 15 p. Mots-clés : flow  (dynamics);  turbulence;  eddies  (fluid  dynamics);  computer  simulation;  Reynolds  number;  polishing  equipment;  eigenfunctions;  channel  flow Résumé : We use proper orthogonal decomposition (POD) to estimate the flow in the near-wall region based on information from the outer buffer layer. Our goal is to assess how the flow structures in the inner wall region are connected to those further away from the wall, and to investigate the nature of the coupling between the inner and the outer region in the POD framework. Reconstructions are carried out for numerical simulations of a plane channel flow at two different Reynolds numbers. We show that elongated structures with a spanwise wavelength smaller than a critical value tend to be concentrated in the inner layer. The critical wavelength is shown to scale with the inner layer height, and interactions between the inner and the outer layer appear to take place predominantly over a self-similar, height-dependent, range of wavenumbers, in agreement with Townsend’s attached eddy hypothesis. The reconstructed field appears to capture an adequate energy content and to remain correlated with the real field even close to the wall, which reflects the persistence of energetic structures over the extent of the buffer layer. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Review of hydraulic roughness scales in the fully rough regime / Karen A. Flack in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Titre : Review of hydraulic roughness scales in the fully rough regime Type de document : texte imprimé Auteurs : Karen A. Flack, Auteur ; Michael P. Schultz, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Surface  roughness Résumé : A review of predictive methods used to determine the frictional drag on a rough surface is presented. These methods utilize a wide range of roughness scales, including roughness height, pitch, density, and shape parameters. Most of these scales were developed for regular roughness, limiting their applicability to predict the drag for many engineering flows. A new correlation is proposed to estimate the frictional drag for a surface covered with three-dimensional, irregular roughness in the fully rough regime. The correlation relies solely on a measurement of the surface roughness profile and builds on previous work utilizing moments of the surface statistics. A relationship is given for the equivalent sandgrain roughness height as a function of the root-mean-square roughness height and the skewness of the roughness probability density function. Boundary layer similarity scaling then allows the overall frictional drag coefficient to be determined as a function of the ratio of the equivalent sandgrain roughness height to length of the surface. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Review of hydraulic roughness scales in the fully rough regime [texte imprimé] / Karen A. Flack, Auteur ; Michael P. Schultz, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Mots-clés : Surface  roughness Résumé : A review of predictive methods used to determine the frictional drag on a rough surface is presented. These methods utilize a wide range of roughness scales, including roughness height, pitch, density, and shape parameters. Most of these scales were developed for regular roughness, limiting their applicability to predict the drag for many engineering flows. A new correlation is proposed to estimate the frictional drag for a surface covered with three-dimensional, irregular roughness in the fully rough regime. The correlation relies solely on a measurement of the surface roughness profile and builds on previous work utilizing moments of the surface statistics. A relationship is given for the equivalent sandgrain roughness height as a function of the root-mean-square roughness height and the skewness of the roughness probability density function. Boundary layer similarity scaling then allows the overall frictional drag coefficient to be determined as a function of the ratio of the equivalent sandgrain roughness height to length of the surface. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

CFD simulation of the bubbling and slugging gas-solid fluidized beds / Seyyed Hossein Hosseini in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Titre : CFD simulation of the bubbling and slugging gas-solid fluidized beds Type de document : texte imprimé Auteurs : Seyyed Hossein Hosseini, Auteur ; Wenqi Zhong, Auteur ; Mohsen Nasr Esfahany, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : temperature;  particulate  matter;  drag  (fluid  dynamics);  simulation;  fluidization;  computational  fluid  dynamics;  equations;  errors;  fluidized  beds;  pressure  drop Résumé : A two-dimensional transient Eulerian model integrating the kinetic theory for emulsion phase is used to simulate the bubbling and slugging gas-solid fluidized beds, including the Geldart B and D particles, respectively. CFD results show that utilizing an algebraic granular temperature equation, instead of a full granular temperature, one leads to a significant reduction in computational time without loosing accuracy. Different drag models have been examined in the current study. CFD results show that the Syamlal–O’Brien and Di Felice adjusted drag models, based on minimum fluidization velocity, are not suitable for the bed, including coarse particles (Geldart group B). The Gidaspow drag model displays better results in comparison with the others. A good agreement with the available experimental data and the researcher’s findings has been reached quantitatively and qualitatively. The proposed model can reasonably be used for simulation of slugging fluidized beds. This study reduces the computational error compared with the previous works. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] CFD simulation of the bubbling and slugging gas-solid fluidized beds [texte imprimé] / Seyyed Hossein Hosseini, Auteur ; Wenqi Zhong, Auteur ; Mohsen Nasr Esfahany, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Mots-clés : temperature;  particulate  matter;  drag  (fluid  dynamics);  simulation;  fluidization;  computational  fluid  dynamics;  equations;  errors;  fluidized  beds;  pressure  drop Résumé : A two-dimensional transient Eulerian model integrating the kinetic theory for emulsion phase is used to simulate the bubbling and slugging gas-solid fluidized beds, including the Geldart B and D particles, respectively. CFD results show that utilizing an algebraic granular temperature equation, instead of a full granular temperature, one leads to a significant reduction in computational time without loosing accuracy. Different drag models have been examined in the current study. CFD results show that the Syamlal–O’Brien and Di Felice adjusted drag models, based on minimum fluidization velocity, are not suitable for the bed, including coarse particles (Geldart group B). The Gidaspow drag model displays better results in comparison with the others. A good agreement with the available experimental data and the researcher’s findings has been reached quantitatively and qualitatively. The proposed model can reasonably be used for simulation of slugging fluidized beds. This study reduces the computational error compared with the previous works. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Implicit LES predictions of the cavitating flow on a propeller / Rickard E. Bensow in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Titre : Implicit LES predictions of the cavitating flow on a propeller Type de document : texte imprimé Auteurs : Rickard E. Bensow, Auteur ; Göran Bark, Auteur Année de publication : 2010 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  mass  transfer;  cavitation;  wakes;  modeling;  cavities;  propellers;  inflow Résumé : We describe an approach to simulate dynamic cavitation behavior based on large eddy simulation of the governing flow, using an implicit approach for the subgrid terms together with a wall model and a single fluid, two-phase mixture description of the cavitation combined with a finite rate mass transfer model. The pressure-velocity coupling is handled using a PISO algorithm with a modified pressure equation for improved stability when the mass transfer terms are active. The computational model is first applied to a propeller flow in homogeneous inflow in both wetted and cavitating conditions and then tested in an artificial wake condition yielding a dynamic cavitation behavior. Although the predicted cavity extent shows discrepancy with the experimental data, the most important cavitation mechanisms are present in the simulation, including internal jets and leading edge desinence. Based on the ability of the model to predict these mechanisms, we believe that numerical assessment of the risk of cavitation nuisance, such as erosion or noise, is tangible in the near future. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Implicit LES predictions of the cavitating flow on a propeller [texte imprimé] / Rickard E. Bensow, Auteur ; Göran Bark, Auteur . - 2010 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 10 p. Mots-clés : pressure;  flow  (dynamics);  mass  transfer;  cavitation;  wakes;  modeling;  cavities;  propellers;  inflow Résumé : We describe an approach to simulate dynamic cavitation behavior based on large eddy simulation of the governing flow, using an implicit approach for the subgrid terms together with a wall model and a single fluid, two-phase mixture description of the cavitation combined with a finite rate mass transfer model. The pressure-velocity coupling is handled using a PISO algorithm with a modified pressure equation for improved stability when the mass transfer terms are active. The computational model is first applied to a propeller flow in homogeneous inflow in both wetted and cavitating conditions and then tested in an artificial wake condition yielding a dynamic cavitation behavior. Although the predicted cavity extent shows discrepancy with the experimental data, the most important cavitation mechanisms are present in the simulation, including internal jets and leading edge desinence. Based on the ability of the model to predict these mechanisms, we believe that numerical assessment of the risk of cavitation nuisance, such as erosion or noise, is tangible in the near future. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

An examination of trapped bubbles for viscous drag reduction on submerged surfaces / Kelly A. Stephani in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 09 p. Titre : An examination of trapped bubbles for viscous drag reduction on submerged surfaces Type de document : texte imprimé Auteurs : Kelly A. Stephani, Auteur ; David B. Goldstein, Auteur Année de publication : 2010 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  measurement;  drag  (fluid  dynamics);  Reynolds  number;  bubbles;  drag  reduction;  flat  plates Résumé : Viscous drag reduction on a submerged surface can be obtained both in the limit of an unbroken gas film coating the solid and in the nanobubble or perhaps microbubble coating regime when an air layer is created with superhydrophobic coatings. We examine an intermediate bubble size regime with a trapped-bubble array (TBA) formed in a tap water environment using electrolysis to grow and maintain bubbles in thousands of millimeter-sized holes on a solid surface. We show that even though surface tension is sufficient to stabilize bubbles in a TBA against hydrostatic and shear forces beneath a turbulent boundary layer, no drag reduction is obtained. Drag measurements were acquired over Reynolds numbers based on plate length ranging from 7.2×104 DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] An examination of trapped bubbles for viscous drag reduction on submerged surfaces [texte imprimé] / Kelly A. Stephani, Auteur ; David B. Goldstein, Auteur . - 2010 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 09 p. Mots-clés : flow  (dynamics);  measurement;  drag  (fluid  dynamics);  Reynolds  number;  bubbles;  drag  reduction;  flat  plates Résumé : Viscous drag reduction on a submerged surface can be obtained both in the limit of an unbroken gas film coating the solid and in the nanobubble or perhaps microbubble coating regime when an air layer is created with superhydrophobic coatings. We examine an intermediate bubble size regime with a trapped-bubble array (TBA) formed in a tap water environment using electrolysis to grow and maintain bubbles in thousands of millimeter-sized holes on a solid surface. We show that even though surface tension is sufficient to stabilize bubbles in a TBA against hydrostatic and shear forces beneath a turbulent boundary layer, no drag reduction is obtained. Drag measurements were acquired over Reynolds numbers based on plate length ranging from 7.2×104 DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

On the suppression of vortex shedding from circular cylinders using detached short splitter-plates / Behzad Ghadiri Dehkordi in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 04 p. Titre : On the suppression of vortex shedding from circular cylinders using detached short splitter-plates Type de document : texte imprimé Auteurs : Behzad Ghadiri Dehkordi, Auteur ; Hamed Houri Jafari, Auteur Année de publication : 2010 Article en page(s) : 04 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : force;  pressure;  flow  (dynamics);  drag  (fluid  dynamics);  engineering  simulation;  plates  (structures);  circular  cylinders;  cylinders;  vortex  shedding Résumé : Flow over a circular cylinder with detached short splitter-plates is numerically simulated in order to assess the suppression of periodic vortex shedding. A finite-volume solver based on the Cartesian-staggered grid is implemented, and the ghost-cell method in conjunction with Great-Source-Term technique is employed in order to enforce directly the no-slip condition on the cylinder boundary. The accuracy of the solver is validated by simulation of the flow around a single circular cylinder. The results are in good agreement with the experimental data reported in the literature. Finally, the flows over a circular cylinder with splitter-plate in its downstream (off and on the centerline) are computed in Re=40 as a nonvortex shedding case and in Re=100 and 150 as cases with vortex shedding effects. The same simulations are also performed for the case where dual splitter-plates are in a parallel arrangement embedded in the downstream of the cylinder. The optimum location of the splitter-plate to achieve maximum reduction in the lift and drag forces is determined. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] On the suppression of vortex shedding from circular cylinders using detached short splitter-plates [texte imprimé] / Behzad Ghadiri Dehkordi, Auteur ; Hamed Houri Jafari, Auteur . - 2010 . - 04 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 04 p. Mots-clés : force;  pressure;  flow  (dynamics);  drag  (fluid  dynamics);  engineering  simulation;  plates  (structures);  circular  cylinders;  cylinders;  vortex  shedding Résumé : Flow over a circular cylinder with detached short splitter-plates is numerically simulated in order to assess the suppression of periodic vortex shedding. A finite-volume solver based on the Cartesian-staggered grid is implemented, and the ghost-cell method in conjunction with Great-Source-Term technique is employed in order to enforce directly the no-slip condition on the cylinder boundary. The accuracy of the solver is validated by simulation of the flow around a single circular cylinder. The results are in good agreement with the experimental data reported in the literature. Finally, the flows over a circular cylinder with splitter-plate in its downstream (off and on the centerline) are computed in Re=40 as a nonvortex shedding case and in Re=100 and 150 as cases with vortex shedding effects. The same simulations are also performed for the case where dual splitter-plates are in a parallel arrangement embedded in the downstream of the cylinder. The optimum location of the splitter-plate to achieve maximum reduction in the lift and drag forces is determined. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Buoyancy effects on thermal boundary layer over a vertical plate with a convective surface boundary condition / O. D. Makinde in Transactions of the ASME . Journal of fluids engineering, Vol. 132 N° 4 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 04 p. Titre : Buoyancy effects on thermal boundary layer over a vertical plate with a convective surface boundary condition Type de document : texte imprimé Auteurs : O. D. Makinde, Auteur ; P. O. Olanrewaju, Auteur Année de publication : 2010 Article en page(s) : 04 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : buoyancy;  temperature;  fluids;  boundary  layers;  convection;  boundary-value  problems;  prandtl  number;  vertical  plates;  thermal  boundary  layers Résumé : This study aims to analyze the effects of thermal buoyancy on the laminar boundary layer about a vertical plate in a uniform stream of fluid under a convective surface boundary condition. Using a similarity variable, the governing nonlinear partial differential equations have been transformed into a set of coupled nonlinear ordinary differential equations, which are solved numerically by applying shooting iteration technique together with fourth-order Runge–Kutta integration scheme. The variations in dimensionless surface temperature and fluid-solid interface characteristics for different values of Prandtl number (Pr), local Grashof number Grx, and local convective heat transfer parameter Bix are graphed and tabulated. A comparison with previously published results on special case of the problem shows excellent agreement. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Buoyancy effects on thermal boundary layer over a vertical plate with a convective surface boundary condition [texte imprimé] / O. D. Makinde, Auteur ; P. O. Olanrewaju, Auteur . - 2010 . - 04 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 132 N° 4 (Avril 2010) . - 04 p. Mots-clés : buoyancy;  temperature;  fluids;  boundary  layers;  convection;  boundary-value  problems;  prandtl  number;  vertical  plates;  thermal  boundary  layers Résumé : This study aims to analyze the effects of thermal buoyancy on the laminar boundary layer about a vertical plate in a uniform stream of fluid under a convective surface boundary condition. Using a similarity variable, the governing nonlinear partial differential equations have been transformed into a set of coupled nonlinear ordinary differential equations, which are solved numerically by applying shooting iteration technique together with fourth-order Runge–Kutta integration scheme. The variations in dimensionless surface temperature and fluid-solid interface characteristics for different values of Prandtl number (Pr), local Grashof number Grx, and local convective heat transfer parameter Bix are graphed and tabulated. A comparison with previously published results on special case of the problem shows excellent agreement. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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