Dépouillements

Modeling of pumping performance of labyrinth screw pump (LSP) by 2D Reynolds stress equations / Runmei Ma in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 05 p. Titre : Modeling of pumping performance of labyrinth screw pump (LSP) by 2D Reynolds stress equations Type de document : texte imprimé Auteurs : Runmei Ma, Auteur ; Kuisheng Wang, Auteur Année de publication : 2009 Article en page(s) : 05 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : screws;  thread;  clearances  (engineering);  pumps;  equations;  laser  hardening;  stress;  modeling Résumé : By using Prandtl’s mixing length theory to model two-dimensional Reynolds stress equations, the pumping performance of a labyrinth screw pump (LSP) is studied and several key parameters are empirically determined. As a result, two innovative concepts, a cell head coefficient Kf and a pump total head coefficient Kb, are proposed. A simple empirical equation quantifying the effects of the main geometric parameters of the threads on the pump performance is obtained and compared with Golubiev’s experimental results (1965, “Studies on Seal for Rotating Shafts of High-Pressure Pumps,” Wear, 8, pp. 270–288; 1981, Labyrinth-Screw Pumps and Seals for Corrosive Media, 2nd ed., Mashinostroenie, Moscow, pp. 34–49). Both theoretical study and Golubiev’s results indicate that with an increase in screw lead, Kf increases while Kb decreases. Kf is inversely proportional to power of screw-sleeve relative diametrical clearance, and the power exponent varies with different shapes of thread. Finally, Kf decreases with an increase in the relative depth of the thread groove over a wide range. Furthermore, some empirical relations between Kf and screw lead, the screw-sleeve relative diametrical clearance and the relative depth of thread groove are fitted, respectively, based on the derived relation between Kf and thread geometric parameters and Golubiev’s experimental data, which would provide a theoretical basis for LSP design. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Modeling of pumping performance of labyrinth screw pump (LSP) by 2D Reynolds stress equations [texte imprimé] / Runmei Ma, Auteur ; Kuisheng Wang, Auteur . - 2009 . - 05 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 05 p. Mots-clés : screws;  thread;  clearances  (engineering);  pumps;  equations;  laser  hardening;  stress;  modeling Résumé : By using Prandtl’s mixing length theory to model two-dimensional Reynolds stress equations, the pumping performance of a labyrinth screw pump (LSP) is studied and several key parameters are empirically determined. As a result, two innovative concepts, a cell head coefficient Kf and a pump total head coefficient Kb, are proposed. A simple empirical equation quantifying the effects of the main geometric parameters of the threads on the pump performance is obtained and compared with Golubiev’s experimental results (1965, “Studies on Seal for Rotating Shafts of High-Pressure Pumps,” Wear, 8, pp. 270–288; 1981, Labyrinth-Screw Pumps and Seals for Corrosive Media, 2nd ed., Mashinostroenie, Moscow, pp. 34–49). Both theoretical study and Golubiev’s results indicate that with an increase in screw lead, Kf increases while Kb decreases. Kf is inversely proportional to power of screw-sleeve relative diametrical clearance, and the power exponent varies with different shapes of thread. Finally, Kf decreases with an increase in the relative depth of the thread groove over a wide range. Furthermore, some empirical relations between Kf and screw lead, the screw-sleeve relative diametrical clearance and the relative depth of thread groove are fitted, respectively, based on the derived relation between Kf and thread geometric parameters and Golubiev’s experimental data, which would provide a theoretical basis for LSP design. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Aerodynamic performance of blade tip end-plates designed for low-noise operation in axial flow fans / Alessandro Corsini in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 13 p. Titre : Aerodynamic performance of blade tip end-plates designed for low-noise operation in axial flow fans Type de document : texte imprimé Auteurs : Alessandro Corsini, Auteur ; Anthony G. Sheard, Auteur ; Franco Rispoli, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : blade-tip;  passive  noise  control;  axial  flow  fan Résumé : This study assesses the effectiveness of modified blade-tip configurations in achieving passive noise control in industrial fans. The concepts developed here, which are based on the addition of end-plates at the fan-blade tip, are shown to have a beneficial effect on the fan aeroacoustic signature as a result of the changes they induce in tip-leakage-flow behavior. The aerodynamic merits of the proposed blade-tip concepts are investigated by experimental and computational studies in a fully ducted configuration. The flow mechanisms in the blade-tip region are correlated with the specific end-plate design features, and their role in the creation of overall acoustic emissions is clarified. The tip-leakage flows of the fans are analyzed in terms of vortex structure, chordwise leakage flow, and loading distribution. Rotor losses are also investigated. The modifications to blade-tip geometry are found to have marked effects on the multiple vortex behaviors of leakage flow as a result of changes in the near-wall fluid flow paths on both blade surfaces. The improvements in rotor efficiency are assessed and correlated with the control of tip-leakage flows produced by the modified tip end-plates. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Aerodynamic performance of blade tip end-plates designed for low-noise operation in axial flow fans [texte imprimé] / Alessandro Corsini, Auteur ; Anthony G. Sheard, Auteur ; Franco Rispoli, Auteur . - 2009 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 13 p. Mots-clés : blade-tip;  passive  noise  control;  axial  flow  fan Résumé : This study assesses the effectiveness of modified blade-tip configurations in achieving passive noise control in industrial fans. The concepts developed here, which are based on the addition of end-plates at the fan-blade tip, are shown to have a beneficial effect on the fan aeroacoustic signature as a result of the changes they induce in tip-leakage-flow behavior. The aerodynamic merits of the proposed blade-tip concepts are investigated by experimental and computational studies in a fully ducted configuration. The flow mechanisms in the blade-tip region are correlated with the specific end-plate design features, and their role in the creation of overall acoustic emissions is clarified. The tip-leakage flows of the fans are analyzed in terms of vortex structure, chordwise leakage flow, and loading distribution. Rotor losses are also investigated. The modifications to blade-tip geometry are found to have marked effects on the multiple vortex behaviors of leakage flow as a result of changes in the near-wall fluid flow paths on both blade surfaces. The improvements in rotor efficiency are assessed and correlated with the control of tip-leakage flows produced by the modified tip end-plates. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Experimental Evidence of Hydroacoustic Pressure Waves in a Francis Turbine Elbow Draft Tube for Low Discharge Conditions / Jorge Arpe in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Titre : Experimental Evidence of Hydroacoustic Pressure Waves in a Francis Turbine Elbow Draft Tube for Low Discharge Conditions Type de document : texte imprimé Auteurs : Jorge Arpe, Auteur ; Nicolet, Christophe, Auteur ; François Avellan, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : three-dimensional  unsteady  flow;  Francis  turbine Résumé : The complex three-dimensional unsteady flow developing in the draft tube of a Francis turbine is responsible for pressure fluctuations, which could prevent the whole hydropower plant from operating safely. Indeed, the Francis draft tube is subjected to inlet swirling flow, divergent cross section, and the change of flow direction. As a result, in low discharge off-design operating conditions, a cavitation helical vortex, so-called the vortex rope develops in the draft tube and induces pressure fluctuations in the range of 0.2–0.4 times the runner frequency. This paper presents the extensive unsteady wall pressure measurements performed in the elbow draft tube of a high specific speed Francis turbine scale model at low discharge and at usual plant value of the Thoma cavitation number. The investigation is undertaken for operating conditions corresponding to low discharge, i.e., 0.65–0.85 times the design discharge, which exhibits pressure fluctuations at surprisingly high frequency value, between 2 and 4 times the runner rotation frequency. The pressure fluctuation measurements performed with 104 pressure transducers distributed on the draft tube wall, make apparent in the whole draft tube a fundamental frequency value at 2.5 times the runner frequency. Moreover, the modulations between this frequency with the vortex rope precession frequency are pointed out. The phase shift analysis performed for 2.5 times the runner frequency enables the identification of a pressure wave propagation phenomenon and indicates the location of the corresponding pressure fluctuation excitation source in the elbow; hydroacoustic waves propagate from this source both upstream and downstream the draft tube. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Experimental Evidence of Hydroacoustic Pressure Waves in a Francis Turbine Elbow Draft Tube for Low Discharge Conditions [texte imprimé] / Jorge Arpe, Auteur ; Nicolet, Christophe, Auteur ; François Avellan, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Mots-clés : three-dimensional  unsteady  flow;  Francis  turbine Résumé : The complex three-dimensional unsteady flow developing in the draft tube of a Francis turbine is responsible for pressure fluctuations, which could prevent the whole hydropower plant from operating safely. Indeed, the Francis draft tube is subjected to inlet swirling flow, divergent cross section, and the change of flow direction. As a result, in low discharge off-design operating conditions, a cavitation helical vortex, so-called the vortex rope develops in the draft tube and induces pressure fluctuations in the range of 0.2–0.4 times the runner frequency. This paper presents the extensive unsteady wall pressure measurements performed in the elbow draft tube of a high specific speed Francis turbine scale model at low discharge and at usual plant value of the Thoma cavitation number. The investigation is undertaken for operating conditions corresponding to low discharge, i.e., 0.65–0.85 times the design discharge, which exhibits pressure fluctuations at surprisingly high frequency value, between 2 and 4 times the runner rotation frequency. The pressure fluctuation measurements performed with 104 pressure transducers distributed on the draft tube wall, make apparent in the whole draft tube a fundamental frequency value at 2.5 times the runner frequency. Moreover, the modulations between this frequency with the vortex rope precession frequency are pointed out. The phase shift analysis performed for 2.5 times the runner frequency enables the identification of a pressure wave propagation phenomenon and indicates the location of the corresponding pressure fluctuation excitation source in the elbow; hydroacoustic waves propagate from this source both upstream and downstream the draft tube. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Impact of orifice length/diameter ratio on 90 deg sharp-edge orifice flow with manifold passage cross flow / W. H. Nurick in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 10 p. Titre : Impact of orifice length/diameter ratio on 90 deg sharp-edge orifice flow with manifold passage cross flow Type de document : texte imprimé Auteurs : W. H. Nurick, Auteur ; D. G. Talley, Auteur ; P. A. Strakey, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  cavitation;  manifolds;  cross-flow;  pressure Résumé : The available information describing the various stages of flow conditions that occur as the flow transitions from noncavitation to cavitation (turbulent flow), supercavitation, and finally separation in sharp-edge 90 deg orifices is extensive. However, although sharp-edge orifices in cross flow represent a significant number of injection schemes inherent in many applications, data for this configuration are sparse or nonexistent. This study is intended to increase the database and understanding of the driving variables affecting the flow in all of these conditions. Tests were carried out in a unique test facility capable of achieving large variations in back pressure, flowrate, and operating upstream pressure. The configuration and test ranges of this study includes orifice length/diameter ratios from 2 to 10, upstream pressures from 7.03 kg/cm2 to 105.1 kg/cm2, orifice/manifold area ratio of 0.028 to 0.082, and manifold cross flow velocity of from 410 cm/s to 1830 cm/s. The results for these small area ratio configurations support two different first order models, one for cavitation and the other noncavitation both in turbulent flow. Under cavitation conditions the discharge coefficient is related to the contraction coefficient and the cavitation parameter to the 1/2 power. In the noncavitation flow regime the head loss is related to the loss coefficient and the dynamic pressure at the orifice exit. Both the head loss and contraction coefficient were found to be a strong function of the ratio of manifold/orifice exit velocity. Equations are provided defining the relationships that allow determination of the contraction coefficient, discharge coefficient, and head loss between the contraction coefficient, as well as the loss coefficient and operating conditions. Cavitation parameter values for cavitation inception, cavitation, and supercavitation are also provided. The potential flow theory was shown to predict the contraction coefficient when upstream (manifold to vena-contracta) losses are minimal. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Impact of orifice length/diameter ratio on 90 deg sharp-edge orifice flow with manifold passage cross flow [texte imprimé] / W. H. Nurick, Auteur ; D. G. Talley, Auteur ; P. A. Strakey, Auteur . - 2009 . - 10 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 10 p. Mots-clés : flow  (dynamics);  cavitation;  manifolds;  cross-flow;  pressure Résumé : The available information describing the various stages of flow conditions that occur as the flow transitions from noncavitation to cavitation (turbulent flow), supercavitation, and finally separation in sharp-edge 90 deg orifices is extensive. However, although sharp-edge orifices in cross flow represent a significant number of injection schemes inherent in many applications, data for this configuration are sparse or nonexistent. This study is intended to increase the database and understanding of the driving variables affecting the flow in all of these conditions. Tests were carried out in a unique test facility capable of achieving large variations in back pressure, flowrate, and operating upstream pressure. The configuration and test ranges of this study includes orifice length/diameter ratios from 2 to 10, upstream pressures from 7.03 kg/cm2 to 105.1 kg/cm2, orifice/manifold area ratio of 0.028 to 0.082, and manifold cross flow velocity of from 410 cm/s to 1830 cm/s. The results for these small area ratio configurations support two different first order models, one for cavitation and the other noncavitation both in turbulent flow. Under cavitation conditions the discharge coefficient is related to the contraction coefficient and the cavitation parameter to the 1/2 power. In the noncavitation flow regime the head loss is related to the loss coefficient and the dynamic pressure at the orifice exit. Both the head loss and contraction coefficient were found to be a strong function of the ratio of manifold/orifice exit velocity. Equations are provided defining the relationships that allow determination of the contraction coefficient, discharge coefficient, and head loss between the contraction coefficient, as well as the loss coefficient and operating conditions. Cavitation parameter values for cavitation inception, cavitation, and supercavitation are also provided. The potential flow theory was shown to predict the contraction coefficient when upstream (manifold to vena-contracta) losses are minimal. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

An experimental investigation of the flowfield and dust resuspension due to idealized human walking / Yoshihiro Kubota in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 06 p. Titre : An experimental investigation of the flowfield and dust resuspension due to idealized human walking Type de document : texte imprimé Auteurs : Yoshihiro Kubota, Auteur ; Joseph W. Hall, Auteur ; Hiroshi Higuchi, Auteur Année de publication : 2009 Article en page(s) : 06 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : particulate  matter;  motion;  flow  visualization;  disks;  vortices;  flow  (dynamics);  mechanisms;  dust Résumé : In order to address how human foot movement causes particles to be resuspended from the floor, particle flow visualization and particle image velocimetry (PIV) measurements were performed on a simplified model of the human walking motion; a disk moving normal to the floor. Flow visualization of particles, seeded initially on the ground, indicates that particles are resuspended by both the downward and upward motions of the walking process. On both the upstep and the downstep, particle resuspension occurs due to a high velocity wall jet, forming between the wall and the disk in general accord with the mechanism for particle resuspension put forth by and (2007, “Particle Levitation Due to a Uniformly Descending Flat Object,” Aerosol Sci. Technol., 41, pp. 33–42). Large-scale ring vortex structures were formed on both the downstep and the upstep, and did not cause particle resuspension, but were extremely effective at quickly moving the already resuspended particles away from the wall. By varying the seeding of the particles, it was determined that only particles underneath and toward the outer edge of the disk are resuspended. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] An experimental investigation of the flowfield and dust resuspension due to idealized human walking [texte imprimé] / Yoshihiro Kubota, Auteur ; Joseph W. Hall, Auteur ; Hiroshi Higuchi, Auteur . - 2009 . - 06 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 06 p. Mots-clés : particulate  matter;  motion;  flow  visualization;  disks;  vortices;  flow  (dynamics);  mechanisms;  dust Résumé : In order to address how human foot movement causes particles to be resuspended from the floor, particle flow visualization and particle image velocimetry (PIV) measurements were performed on a simplified model of the human walking motion; a disk moving normal to the floor. Flow visualization of particles, seeded initially on the ground, indicates that particles are resuspended by both the downward and upward motions of the walking process. On both the upstep and the downstep, particle resuspension occurs due to a high velocity wall jet, forming between the wall and the disk in general accord with the mechanism for particle resuspension put forth by and (2007, “Particle Levitation Due to a Uniformly Descending Flat Object,” Aerosol Sci. Technol., 41, pp. 33–42). Large-scale ring vortex structures were formed on both the downstep and the upstep, and did not cause particle resuspension, but were extremely effective at quickly moving the already resuspended particles away from the wall. By varying the seeding of the particles, it was determined that only particles underneath and toward the outer edge of the disk are resuspended. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

An efficient quasi-2D simulation of waterhammer in complex pipe systems / Huan-Feng Duan in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Titre : An efficient quasi-2D simulation of waterhammer in complex pipe systems Type de document : texte imprimé Auteurs : Huan-Feng Duan, Auteur ; Mohamed S. Ghidaoui, Auteur ; Yeou-Koung Tung, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pipes;  equations;  simulation;  junctions;  valves;  bifurcation;  boundary-value  problems;  numerical  stability Résumé : An efficient quasi-2D numerical waterhammer model for turbulent waterhammer flows has been previously developed for a single pipe system (reservoir-pipe-valve system). Basic boundary conditions, such as valves, reservoirs, and external flows, were also implemented. This paper extends this previously developed efficient scheme to a general model for a multipipe system. More specifically, an approach for matching the family of characteristic equations in each pipe at a junction of two or more pipes is proposed. In addition, the numerical stability conditions of the efficient scheme are investigated using the Von Neumann method. The resulting model is verified against experimental data and then applied to different complex systems involving pipes in series, branching, and network. Using this model, the effects of unsteady friction in complex pipe systems are examined and analyzed in this paper. From the case studies, it is found that the quasi-2D model is highly efficient, robust, and suitable for application to waterhammer problems in real complex pipe system. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] An efficient quasi-2D simulation of waterhammer in complex pipe systems [texte imprimé] / Huan-Feng Duan, Auteur ; Mohamed S. Ghidaoui, Auteur ; Yeou-Koung Tung, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Mots-clés : pipes;  equations;  simulation;  junctions;  valves;  bifurcation;  boundary-value  problems;  numerical  stability Résumé : An efficient quasi-2D numerical waterhammer model for turbulent waterhammer flows has been previously developed for a single pipe system (reservoir-pipe-valve system). Basic boundary conditions, such as valves, reservoirs, and external flows, were also implemented. This paper extends this previously developed efficient scheme to a general model for a multipipe system. More specifically, an approach for matching the family of characteristic equations in each pipe at a junction of two or more pipes is proposed. In addition, the numerical stability conditions of the efficient scheme are investigated using the Von Neumann method. The resulting model is verified against experimental data and then applied to different complex systems involving pipes in series, branching, and network. Using this model, the effects of unsteady friction in complex pipe systems are examined and analyzed in this paper. From the case studies, it is found that the quasi-2D model is highly efficient, robust, and suitable for application to waterhammer problems in real complex pipe system. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Joint computational/experimental aerodynamic study of a simplified tractor/trailer geometry / Anwar Ahmed in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Titre : Joint computational/experimental aerodynamic study of a simplified tractor/trailer geometry Type de document : texte imprimé Auteurs : Anwar Ahmed, Auteur ; Subrahmanya P. Veluri, Auteur ; Christopher J. Roy, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : tractor  trailer;  aerodynamic  study;  Reynolds  averaged  Navier–Stokes  simulations Résumé : Steady-state Reynolds averaged Navier–Stokes (RANS) simulations are presented for the three-dimensional flow over a generic tractor trailer placed in the Auburn University 3×4 ft2 suction wind tunnel. The width of the truck geometry is 10 in., and the height and length of the trailer are 1.392 and 3.4 times the width, respectively. The computational model of the wind tunnel is validated by comparing the numerical results with the data from the empty wind tunnel experiments. The comparisons include the boundary layer properties at three different locations on the floor of the test section and the flow angularity at the beginning of the test section. Three grid levels are used for the simulation of the truck geometry placed in the test section of the wind tunnel. The coarse mesh consists of 3.4×106 cells, the medium mesh consists of 11.2×106 cells and the fine mesh consists of 25.8×106 cells. The turbulence models used for both the empty tunnel simulations and the truck geometry placed in the wind tunnel are the standard Wilcox 1998 k-ω model, the SST k-ω model, the standard k-ε model, and the Spalart–Allmaras model. The surface pressure distributions on the truck geometry and the overall drag are predicted from the simulations and compared with the experimental data. The computational predictions compared well with the experimental data. This study contributes a new validation data set and computations for high Reynolds number bluff-body flows. The validation data set can be used for initial assessment in evaluating RANS models, which will be used for studying the drag or drag trends predicted by the baseline truck geometries. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Joint computational/experimental aerodynamic study of a simplified tractor/trailer geometry [texte imprimé] / Anwar Ahmed, Auteur ; Subrahmanya P. Veluri, Auteur ; Christopher J. Roy, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 09 p. Mots-clés : tractor  trailer;  aerodynamic  study;  Reynolds  averaged  Navier–Stokes  simulations Résumé : Steady-state Reynolds averaged Navier–Stokes (RANS) simulations are presented for the three-dimensional flow over a generic tractor trailer placed in the Auburn University 3×4 ft2 suction wind tunnel. The width of the truck geometry is 10 in., and the height and length of the trailer are 1.392 and 3.4 times the width, respectively. The computational model of the wind tunnel is validated by comparing the numerical results with the data from the empty wind tunnel experiments. The comparisons include the boundary layer properties at three different locations on the floor of the test section and the flow angularity at the beginning of the test section. Three grid levels are used for the simulation of the truck geometry placed in the test section of the wind tunnel. The coarse mesh consists of 3.4×106 cells, the medium mesh consists of 11.2×106 cells and the fine mesh consists of 25.8×106 cells. The turbulence models used for both the empty tunnel simulations and the truck geometry placed in the wind tunnel are the standard Wilcox 1998 k-ω model, the SST k-ω model, the standard k-ε model, and the Spalart–Allmaras model. The surface pressure distributions on the truck geometry and the overall drag are predicted from the simulations and compared with the experimental data. The computational predictions compared well with the experimental data. This study contributes a new validation data set and computations for high Reynolds number bluff-body flows. The validation data set can be used for initial assessment in evaluating RANS models, which will be used for studying the drag or drag trends predicted by the baseline truck geometries. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Spontaneous break of symmetry in unconfined laminar annular jets / Christian Del Taglia in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 08 p. Titre : Spontaneous break of symmetry in unconfined laminar annular jets Type de document : texte imprimé Auteurs : Christian Del Taglia, Auteur ; Alfred Moser, Auteur ; Lars Blum, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : spontaneous  break  of  symmetry;  laminar  annular  jet;  numerical  investigation Résumé : Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Spontaneous break of symmetry in unconfined laminar annular jets [texte imprimé] / Christian Del Taglia, Auteur ; Alfred Moser, Auteur ; Lars Blum, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 08 p. Mots-clés : spontaneous  break  of  symmetry;  laminar  annular  jet;  numerical  investigation Résumé : Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Effect of liquid transparency on laser-induced motion of drops / R. Shukla in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 07 p. Titre : Effect of liquid transparency on laser-induced motion of drops Type de document : texte imprimé Auteurs : R. Shukla, Auteur ; K. A. Sallam, Auteur Année de publication : 2009 Article en page(s) : 07 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : liquid  transparency;  laser-induced  motion;  liquid  drop Résumé : An experimental investigation of the role of liquid transparency in controlling laser-induced motion of liquid drops is carried out. The study was motivated by application to manipulation of liquid drops over a solid substrate. Droplets with diameters of 1–4 mm were propelled on a hydrophobic substrate using a pulsed-laser beam (532 nm, 10 Hz, 3–12 mJ/pulse) with a 0.9 mm diameter fired parallel to the substrate. The test liquid was distilled water whose transparency was varied by adding different concentrations of Rhodamine 6G dye. Motion of the drops was observed using a video camera. Measurements include direction of motion and the distance traveled before the drops come to rest. The present results show that the direction of the motion depends on the drop transparency; opaque drops moved away from the laser beam, whereas transparent drops moved at small angles toward the laser beam. The motion of both transparent and opaque drops was dominated by thermal Marangoni effect; the motion of opaque drops was due to direct heating by the laser beam, whereas in the case of transparent drops, the laser beam was focused near the rear face of the transparent drops to form a spark that pushed the drops in the opposite direction. Energies lower than 3 mJ were incapable of moving the drops, and energies higher than 12 mJ shattered the drops instead of moving them. A phenomenological model was developed for the drop motion to explain the physics behind the phenomenon. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Effect of liquid transparency on laser-induced motion of drops [texte imprimé] / R. Shukla, Auteur ; K. A. Sallam, Auteur . - 2009 . - 07 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 07 p. Mots-clés : liquid  transparency;  laser-induced  motion;  liquid  drop Résumé : An experimental investigation of the role of liquid transparency in controlling laser-induced motion of liquid drops is carried out. The study was motivated by application to manipulation of liquid drops over a solid substrate. Droplets with diameters of 1–4 mm were propelled on a hydrophobic substrate using a pulsed-laser beam (532 nm, 10 Hz, 3–12 mJ/pulse) with a 0.9 mm diameter fired parallel to the substrate. The test liquid was distilled water whose transparency was varied by adding different concentrations of Rhodamine 6G dye. Motion of the drops was observed using a video camera. Measurements include direction of motion and the distance traveled before the drops come to rest. The present results show that the direction of the motion depends on the drop transparency; opaque drops moved away from the laser beam, whereas transparent drops moved at small angles toward the laser beam. The motion of both transparent and opaque drops was dominated by thermal Marangoni effect; the motion of opaque drops was due to direct heating by the laser beam, whereas in the case of transparent drops, the laser beam was focused near the rear face of the transparent drops to form a spark that pushed the drops in the opposite direction. Energies lower than 3 mJ were incapable of moving the drops, and energies higher than 12 mJ shattered the drops instead of moving them. A phenomenological model was developed for the drop motion to explain the physics behind the phenomenon. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

A lattice Boltzmann method based numerical scheme for microchannel flows / S. C. Fu in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 11 p. Titre : A lattice Boltzmann method based numerical scheme for microchannel flows Type de document : texte imprimé Auteurs : S. C. Fu, Auteur ; W. W. F. Leung, Auteur ; R. M. C. So, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : Lattice  Boltzmann  method;  microchannel  flows;  Navier–Stokes  equations Résumé : Conventional lattice Boltzmann method (LBM) is hyperbolic and can be solved locally, explicitly, and efficiently on parallel computers. The LBM has been applied to different types of complex flows with varying degrees of success, and with increased attention focusing on microscale flows now. Due to its small scale, microchannel flows exhibit many interesting phenomena that are not observed in their macroscale counterpart. It is known that the Navier–Stokes equations can still be used to treat microchannel flows if a slip-wall boundary condition is assumed. The setting of boundary conditions in the conventional LBM has been a difficult task, and reliable boundary setting methods are limited. This paper reports on the development of a finite difference LBM (FDLBM) based numerical scheme suitable for microchannel flows to solve the modeled Boltzmann equation using a splitting technique that allows convenient application of a slip-wall boundary condition. Moreover, the fluid viscosity is accounted for as an additional term in the equilibrium particle distribution function, which offers the ability to simulate both Newtonian and non-Newtonian fluids. A two-dimensional nine-velocity lattice model is developed for the numerical simulation. Validation of the FDLBM is carried out against microchannel and microtube flows, a driven cavity flow, and a two-dimensional sudden expansion flow. Excellent agreement is obtained between numerical calculations and analytical solutions of these flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] A lattice Boltzmann method based numerical scheme for microchannel flows [texte imprimé] / S. C. Fu, Auteur ; W. W. F. Leung, Auteur ; R. M. C. So, Auteur . - 2009 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 11 p. Mots-clés : Lattice  Boltzmann  method;  microchannel  flows;  Navier–Stokes  equations Résumé : Conventional lattice Boltzmann method (LBM) is hyperbolic and can be solved locally, explicitly, and efficiently on parallel computers. The LBM has been applied to different types of complex flows with varying degrees of success, and with increased attention focusing on microscale flows now. Due to its small scale, microchannel flows exhibit many interesting phenomena that are not observed in their macroscale counterpart. It is known that the Navier–Stokes equations can still be used to treat microchannel flows if a slip-wall boundary condition is assumed. The setting of boundary conditions in the conventional LBM has been a difficult task, and reliable boundary setting methods are limited. This paper reports on the development of a finite difference LBM (FDLBM) based numerical scheme suitable for microchannel flows to solve the modeled Boltzmann equation using a splitting technique that allows convenient application of a slip-wall boundary condition. Moreover, the fluid viscosity is accounted for as an additional term in the equilibrium particle distribution function, which offers the ability to simulate both Newtonian and non-Newtonian fluids. A two-dimensional nine-velocity lattice model is developed for the numerical simulation. Validation of the FDLBM is carried out against microchannel and microtube flows, a driven cavity flow, and a two-dimensional sudden expansion flow. Excellent agreement is obtained between numerical calculations and analytical solutions of these flows. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Application of Fractional Scaling Analysis to Loss of Coolant Accidents, System Level Scaling for System Depressurization / Wolfgang Wulff in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 13 p. Titre : Application of Fractional Scaling Analysis to Loss of Coolant Accidents, System Level Scaling for System Depressurization Type de document : texte imprimé Auteurs : Wolfgang Wulff, Auteur ; Novak Zuber, Auteur ; Upendra S. Rohatgi, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : nuclear  reactor  primary  systems;  fractional  scaling  analysis Résumé : Fractional scaling analysis (FSA) is demonstrated at the system level. The selected example is depressurization of nuclear reactor primary systems undergoing large- and small-break loss of coolant accidents (LOCA), specifically in two integral test facilities of different sizes and shapes, namely, LOFT and Semiscale. The paper demonstrates (1) the relation between pressure and volume displacement rates in analogy to generalized “effort” and “flow” in interdisciplinary analysis of complex systems and (2) using experimental data that a properly scaled depressurization history applies to both large- and small-break LOCA in two different facilities. FSA, when applied at the system, component, and process levels, serves to synthesize the worldwide wealth of results from analyses and experiments into compact form for efficient storage, transfer, and retrieval of information. The demonstration at the system level shows that during LOCAs the break flow dominates for break sizes between 0.1% and 200% of cold-leg flow cross-sectional area, and that FSA ranks processes quantitatively and thereby objectively in the order of their importance. FSA supersedes the hereunto subjectively implemented phenomena identification and ranking table. FSA readily quantifies scale distortions. FSA reduces significantly the need for and current cost of experiments and analyses. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Application of Fractional Scaling Analysis to Loss of Coolant Accidents, System Level Scaling for System Depressurization [texte imprimé] / Wolfgang Wulff, Auteur ; Novak Zuber, Auteur ; Upendra S. Rohatgi, Auteur . - 2009 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 13 p. Mots-clés : nuclear  reactor  primary  systems;  fractional  scaling  analysis Résumé : Fractional scaling analysis (FSA) is demonstrated at the system level. The selected example is depressurization of nuclear reactor primary systems undergoing large- and small-break loss of coolant accidents (LOCA), specifically in two integral test facilities of different sizes and shapes, namely, LOFT and Semiscale. The paper demonstrates (1) the relation between pressure and volume displacement rates in analogy to generalized “effort” and “flow” in interdisciplinary analysis of complex systems and (2) using experimental data that a properly scaled depressurization history applies to both large- and small-break LOCA in two different facilities. FSA, when applied at the system, component, and process levels, serves to synthesize the worldwide wealth of results from analyses and experiments into compact form for efficient storage, transfer, and retrieval of information. The demonstration at the system level shows that during LOCAs the break flow dominates for break sizes between 0.1% and 200% of cold-leg flow cross-sectional area, and that FSA ranks processes quantitatively and thereby objectively in the order of their importance. FSA supersedes the hereunto subjectively implemented phenomena identification and ranking table. FSA readily quantifies scale distortions. FSA reduces significantly the need for and current cost of experiments and analyses. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Fluid streaming in micro/minibifurcating networks / Z. Zhang in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 8 (Août 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 08 p. Titre : Fluid streaming in micro/minibifurcating networks Type de document : texte imprimé Auteurs : Z. Zhang, Auteur ; M. Krafczyk, Auteur ; A. Fadl, Auteur Année de publication : 2009 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  streaming;  micro-/minichannel  networks;  oscillation Résumé : In this study, we investigate the phenomena of flow streaming in micro-/minichannel networks of symmetrical bifurcations using computer simulations with analytical validation. The phenomena of the flow streaming can be found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no net mass flow (zero-mean velocity) passing through the channels, the discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end while particles near the centerline to drift toward the opposite end. The unique characteristics of flow streaming could be used for various applications. The advantages include enhanced mixing, pumpless fluid propulsion, multichannel fluid distribution, easy system integration, and cost-effective operation. The results of computer simulations showed that oscillation amplitude is the dominant effect on streaming velocity in channel networks. Streaming velocity was directly proportional to the oscillation frequency and can be used as a cost-effective and reliable convective transport means when the particle diffusivity is less than the fluid kinematic viscosity. A considerable amount of work is needed to further study and understand the flow streaming phenomenon. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Fluid streaming in micro/minibifurcating networks [texte imprimé] / Z. Zhang, Auteur ; M. Krafczyk, Auteur ; A. Fadl, Auteur . - 2009 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 8 (Août 2009) . - 08 p. Mots-clés : flow  streaming;  micro-/minichannel  networks;  oscillation Résumé : In this study, we investigate the phenomena of flow streaming in micro-/minichannel networks of symmetrical bifurcations using computer simulations with analytical validation. The phenomena of the flow streaming can be found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no net mass flow (zero-mean velocity) passing through the channels, the discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end while particles near the centerline to drift toward the opposite end. The unique characteristics of flow streaming could be used for various applications. The advantages include enhanced mixing, pumpless fluid propulsion, multichannel fluid distribution, easy system integration, and cost-effective operation. The results of computer simulations showed that oscillation amplitude is the dominant effect on streaming velocity in channel networks. Streaming velocity was directly proportional to the oscillation frequency and can be used as a cost-effective and reliable convective transport means when the particle diffusivity is less than the fluid kinematic viscosity. A considerable amount of work is needed to further study and understand the flow streaming phenomenon. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Exemplaires

Bibliothèque Ecole Nationale Polytechnique d'Alger

Accueil

Se connecter

Météo

Adresse