Dépouillements

Characteristics and control of the draft-tube flow in part-load Francis turbine / Ri-kui Zhang in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 13 p. Titre : Characteristics and control of the draft-tube flow in part-load Francis turbine Type de document : texte imprimé Auteurs : Ri-kui Zhang, Auteur ; Feng Mao, Auteur ; Jie-Zhi Wu, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  stress;  vortices;  ropes Résumé : Under part-load conditions, a Francis turbine often suffers from very severe low-frequency and large-amplitude pressure fluctuation, which is caused by the unsteady motion of vortices (known as “vortex ropes”) in the draft tube. This paper first reports our numerical investigation of relevant complex flow phenomena in the entire draft tube, based on the Reynolds-averaged Navier–Stokes (RANS) equations. We then focus on the physical mechanisms underlying these complex and somewhat chaotic flow phenomena of the draft-tube flow under a part-load condition. The flow stability and robustness are our special concern, since they determine what kind of control methodology will be effective for eliminating or alleviating those adverse phenomena. Our main findings about the flow behavior in the three segments of the draft tube, i.e., the cone inlet, the elbow segment, and the outlet segment with three exits, are as follows. (1) In the cone segment, we reconfirmed a previous finding of our research group based on the turbine’s whole-flow RANS computation that the harmful vortex rope is an inevitable consequence of the global instability of the swirling flow. We further identified that this instability is caused crucially by the reversed axial flow at the inlet of the draft tube. (2) In the elbow segment, we found a reversed flow continued from the inlet cone, which evolves to slow and chaotic motion. There is also a fast forward stream driven by a localized favorable axial pressure gradient, which carries the whole mass flux downstream. The forward stream and reversed flow coexist side-by-side in the elbow, with a complex and unstable shear layer in between. (3) In the outlet segment with three exits, the forward stream always goes through a fixed exit, leaving the other two exits with a chaotic and low-speed fluid motion. Based on these findings, we propose a few control principles to suppress the reversed flow and to eliminate the harmful helical vortex ropes. Of the methods we tested numerically, a simple jet injection in the inlet is proven successful. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Characteristics and control of the draft-tube flow in part-load Francis turbine [texte imprimé] / Ri-kui Zhang, Auteur ; Feng Mao, Auteur ; Jie-Zhi Wu, Auteur . - 2009 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 13 p. Mots-clés : pressure;  flow  (dynamics);  stress;  vortices;  ropes Résumé : Under part-load conditions, a Francis turbine often suffers from very severe low-frequency and large-amplitude pressure fluctuation, which is caused by the unsteady motion of vortices (known as “vortex ropes”) in the draft tube. This paper first reports our numerical investigation of relevant complex flow phenomena in the entire draft tube, based on the Reynolds-averaged Navier–Stokes (RANS) equations. We then focus on the physical mechanisms underlying these complex and somewhat chaotic flow phenomena of the draft-tube flow under a part-load condition. The flow stability and robustness are our special concern, since they determine what kind of control methodology will be effective for eliminating or alleviating those adverse phenomena. Our main findings about the flow behavior in the three segments of the draft tube, i.e., the cone inlet, the elbow segment, and the outlet segment with three exits, are as follows. (1) In the cone segment, we reconfirmed a previous finding of our research group based on the turbine’s whole-flow RANS computation that the harmful vortex rope is an inevitable consequence of the global instability of the swirling flow. We further identified that this instability is caused crucially by the reversed axial flow at the inlet of the draft tube. (2) In the elbow segment, we found a reversed flow continued from the inlet cone, which evolves to slow and chaotic motion. There is also a fast forward stream driven by a localized favorable axial pressure gradient, which carries the whole mass flux downstream. The forward stream and reversed flow coexist side-by-side in the elbow, with a complex and unstable shear layer in between. (3) In the outlet segment with three exits, the forward stream always goes through a fixed exit, leaving the other two exits with a chaotic and low-speed fluid motion. Based on these findings, we propose a few control principles to suppress the reversed flow and to eliminate the harmful helical vortex ropes. Of the methods we tested numerically, a simple jet injection in the inlet is proven successful. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Simulation of turbine blade trailing edge cooling / Jongwook Joo in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 14 p. Titre : Simulation of turbine blade trailing edge cooling Type de document : texte imprimé Auteurs : Jongwook Joo, Auteur ; Durbin, Paul, Auteur Année de publication : 2009 Article en page(s) : 14 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  temperature;  cooling;  turbulence;  eddies  (fluid  dynamics);  simulation;  engineering  simulation;  Reynolds-averaged  Navier–Stokes  equations Résumé : The cause of overprediction of cooling efficiency by unsteady Reynolds averaged simulations of turbine blade trailing edge cooling flow is investigated. This is due to the deficiency in the level of unsteady coherent energy very near to the wall. Farther from the wall, the Reynolds averaged simulation produces the correct level of mixing. Eddy simulations of the instantaneous turbulent eddying produce a close agreement to data on film effectiveness. In particular, they reproduce the reduction in cooling effectiveness toward the trailing edge that has been seen in experiments. The scale adaptive simulation model of Menter and Egorov (2005, “ A Scale-Adaptive Simulation Modeling Using Two-Equation Models,” AIAA Paper No. 2005-1095) is invoked for the eddy simulations. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Simulation of turbine blade trailing edge cooling [texte imprimé] / Jongwook Joo, Auteur ; Durbin, Paul, Auteur . - 2009 . - 14 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 14 p. Mots-clés : flow  (dynamics);  temperature;  cooling;  turbulence;  eddies  (fluid  dynamics);  simulation;  engineering  simulation;  Reynolds-averaged  Navier–Stokes  equations Résumé : The cause of overprediction of cooling efficiency by unsteady Reynolds averaged simulations of turbine blade trailing edge cooling flow is investigated. This is due to the deficiency in the level of unsteady coherent energy very near to the wall. Farther from the wall, the Reynolds averaged simulation produces the correct level of mixing. Eddy simulations of the instantaneous turbulent eddying produce a close agreement to data on film effectiveness. In particular, they reproduce the reduction in cooling effectiveness toward the trailing edge that has been seen in experiments. The scale adaptive simulation model of Menter and Egorov (2005, “ A Scale-Adaptive Simulation Modeling Using Two-Equation Models,” AIAA Paper No. 2005-1095) is invoked for the eddy simulations. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Efficiency improvement of centrifugal reverse pumps / Shahram Derakhshan in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Titre : Efficiency improvement of centrifugal reverse pumps Type de document : texte imprimé Auteurs : Shahram Derakhshan, Auteur ; Bijan Mohammadi, Auteur ; Ahmad Nourbakhsh, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : reverse  pumps;  turbines;  Navier–Stokes  flow  solver Résumé : Pumps as turbines have been successfully applied in a wide range of small hydrosites in the world. Since the overall efficiency of these machines is lower than the overall efficiency of conventional turbines, their application in larger hydrosites is not economical. Therefore, the efficiency improvement of reverse pumps is essential. In this study, by focusing on a pump impeller, the shape of blades was redesigned to reach a higher efficiency in turbine mode using a gradient based optimization algorithm coupled by a 3D Navier–Stokes flow solver. Also, another modification was done by rounding the blades’ leading edges and hub/shroud interface in turbine mode. After each modification, a new impeller was manufactured and tested in the test rig. The efficiency was improved in all measured points by the optimal design of the blade and additional modification as the rounding of the blade’s profile in the impeller inlet and hub/shroud inlet edges in turbine mode. Experimental results confirmed the numerical efficiency improvement in all measured points. This study illustrated that the efficiency of the pump in reverse operation can be improved just by impeller modification. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Efficiency improvement of centrifugal reverse pumps [texte imprimé] / Shahram Derakhshan, Auteur ; Bijan Mohammadi, Auteur ; Ahmad Nourbakhsh, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Mots-clés : reverse  pumps;  turbines;  Navier–Stokes  flow  solver Résumé : Pumps as turbines have been successfully applied in a wide range of small hydrosites in the world. Since the overall efficiency of these machines is lower than the overall efficiency of conventional turbines, their application in larger hydrosites is not economical. Therefore, the efficiency improvement of reverse pumps is essential. In this study, by focusing on a pump impeller, the shape of blades was redesigned to reach a higher efficiency in turbine mode using a gradient based optimization algorithm coupled by a 3D Navier–Stokes flow solver. Also, another modification was done by rounding the blades’ leading edges and hub/shroud interface in turbine mode. After each modification, a new impeller was manufactured and tested in the test rig. The efficiency was improved in all measured points by the optimal design of the blade and additional modification as the rounding of the blade’s profile in the impeller inlet and hub/shroud inlet edges in turbine mode. Experimental results confirmed the numerical efficiency improvement in all measured points. This study illustrated that the efficiency of the pump in reverse operation can be improved just by impeller modification. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Effect of side wind on a simplified car model / Emmanuel Guilmineau in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 12 p. Titre : Effect of side wind on a simplified car model : experimental and numerical analysis Type de document : texte imprimé Auteurs : Emmanuel Guilmineau, Auteur ; Francis Chometon, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : physics;  force;  pressure;  flow  (dynamics);  turbulence;  wakes;  computational  fluid  dynamics;  numerical  analysis;  vehicles;  vortices;  automobiles;  computation;  Reynolds-averaged  Navier–Stokes  equations;  wind;  wind  tunnels;  yaw Résumé : A prior analysis of the effect of steady cross wind on full size cars or models must be conducted when dealing with transient cross wind gust effects on automobiles. The experimental and numerical tests presented in this paper are performed on the Willy square-back test model. This model is realistic compared with a van-type vehicle; its plane underbody surface is parallel to the ground, and separations are limited to the base for moderated yaw angles. Experiments were carried out in the semi-open test section at the Conservatoire National des Arts et Métiers, and computations were performed at the Ecole Centrale de Nantes (ECN). The ISIS-CFD flow solver, developed by the CFD Department of the Fluid Mechanics Laboratory of ECN, used the incompressible unsteady Reynolds-averaged Navier–Stokes equations. In this paper, the results of experiments obtained at a Reynolds number of 0.9×106 are compared with numerical data at the same Reynolds number for steady flows. In both the experiments and numerical results, the yaw angle varies from 0 deg to 30 deg. The comparison between experimental and numerical results obtained for aerodynamic forces, wall pressures, and total pressure maps shows that the unsteady ISIS-CFD solver correctly reflects the physics of steady three-dimensional separated flows around bluff bodies. This encouraging result allows us to move to a second step dealing with the analysis of unsteady separated flows around the Willy model. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Effect of side wind on a simplified car model : experimental and numerical analysis [texte imprimé] / Emmanuel Guilmineau, Auteur ; Francis Chometon, Auteur . - 2009 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 12 p. Mots-clés : physics;  force;  pressure;  flow  (dynamics);  turbulence;  wakes;  computational  fluid  dynamics;  numerical  analysis;  vehicles;  vortices;  automobiles;  computation;  Reynolds-averaged  Navier–Stokes  equations;  wind;  wind  tunnels;  yaw Résumé : A prior analysis of the effect of steady cross wind on full size cars or models must be conducted when dealing with transient cross wind gust effects on automobiles. The experimental and numerical tests presented in this paper are performed on the Willy square-back test model. This model is realistic compared with a van-type vehicle; its plane underbody surface is parallel to the ground, and separations are limited to the base for moderated yaw angles. Experiments were carried out in the semi-open test section at the Conservatoire National des Arts et Métiers, and computations were performed at the Ecole Centrale de Nantes (ECN). The ISIS-CFD flow solver, developed by the CFD Department of the Fluid Mechanics Laboratory of ECN, used the incompressible unsteady Reynolds-averaged Navier–Stokes equations. In this paper, the results of experiments obtained at a Reynolds number of 0.9×106 are compared with numerical data at the same Reynolds number for steady flows. In both the experiments and numerical results, the yaw angle varies from 0 deg to 30 deg. The comparison between experimental and numerical results obtained for aerodynamic forces, wall pressures, and total pressure maps shows that the unsteady ISIS-CFD solver correctly reflects the physics of steady three-dimensional separated flows around bluff bodies. This encouraging result allows us to move to a second step dealing with the analysis of unsteady separated flows around the Willy model. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Passive manipulation of separation-bubble transition using surface modifications / Brian R. McAuliffe in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009)

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 16 p. Titre : Passive manipulation of separation-bubble transition using surface modifications Type de document : texte imprimé Auteurs : Brian R. McAuliffe, Auteur ; Metin I. Yaras, Auteur Année de publication : 2009 Article en page(s) : 16 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  separation  (technology);  turbulence;  Reynolds  number;  shear  (mechanics);  bubbles;  Boundary  layers;  vortices;  airfoils Résumé : Through experiments using two-dimensional particle-image velocimetry (PIV), this paper examines the nature of transition in a separation bubble and manipulations of the resultant breakdown to turbulence through passive means of control. An airfoil was used that provides minimal variation in the separation location over a wide operating range, with various two-dimensional modifications made to the surface for the purpose of manipulating the transition process. The study was conducted under low-freestream-turbulence conditions over a flow Reynolds number range of 28,000–101,000 based on airfoil chord. The spatial nature of the measurements has allowed identification of the dominant flow structures associated with transition in the separated shear layer and the manipulations introduced by the surface modifications. The Kelvin–Helmholtz (K-H) instability is identified as the dominant transition mechanism in the separated shear layer, leading to the roll-up of spanwise vorticity and subsequent breakdown into small-scale turbulence. Similarities with planar free-shear layers are noted, including the frequency of maximum amplification rate for the K-H instability and the vortex-pairing phenomenon initiated by a subharmonic instability. In some cases, secondary pairing events are observed and result in a laminar intervortex region consisting of freestream fluid entrained toward the surface due to the strong circulation of the large-scale vortices. Results of the surface-modification study show that different physical mechanisms can be manipulated to affect the separation, transition, and reattachment processes over the airfoil. These manipulations are also shown to affect the boundary-layer losses observed downstream of reattachment, with all surface-indentation configurations providing decreased losses at the three lowest Reynolds numbers and three of the five configurations providing decreased losses at the highest Reynolds number. The primary mechanisms that provide these manipulations include: suppression of the vortex-pairing phenomenon, which reduces both the shear-layer thickness and the levels of small-scale turbulence; the promotion of smaller-scale turbulence, resulting from the disturbances generated upstream of separation, which provides quicker transition and shorter separation bubbles; the elimination of the separation bubble with transition occurring in an attached boundary layer; and physical disturbance, downstream of separation, of the growing instability waves to manipulate the vortical structures and cause quicker reattachment. DEWEY : 620.1 ISSN : 0098-2202 [article] Passive manipulation of separation-bubble transition using surface modifications [texte imprimé] / Brian R. McAuliffe, Auteur ; Metin I. Yaras, Auteur . - 2009 . - 16 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 16 p. Mots-clés : flow  (dynamics);  separation  (technology);  turbulence;  Reynolds  number;  shear  (mechanics);  bubbles;  Boundary  layers;  vortices;  airfoils Résumé : Through experiments using two-dimensional particle-image velocimetry (PIV), this paper examines the nature of transition in a separation bubble and manipulations of the resultant breakdown to turbulence through passive means of control. An airfoil was used that provides minimal variation in the separation location over a wide operating range, with various two-dimensional modifications made to the surface for the purpose of manipulating the transition process. The study was conducted under low-freestream-turbulence conditions over a flow Reynolds number range of 28,000–101,000 based on airfoil chord. The spatial nature of the measurements has allowed identification of the dominant flow structures associated with transition in the separated shear layer and the manipulations introduced by the surface modifications. The Kelvin–Helmholtz (K-H) instability is identified as the dominant transition mechanism in the separated shear layer, leading to the roll-up of spanwise vorticity and subsequent breakdown into small-scale turbulence. Similarities with planar free-shear layers are noted, including the frequency of maximum amplification rate for the K-H instability and the vortex-pairing phenomenon initiated by a subharmonic instability. In some cases, secondary pairing events are observed and result in a laminar intervortex region consisting of freestream fluid entrained toward the surface due to the strong circulation of the large-scale vortices. Results of the surface-modification study show that different physical mechanisms can be manipulated to affect the separation, transition, and reattachment processes over the airfoil. These manipulations are also shown to affect the boundary-layer losses observed downstream of reattachment, with all surface-indentation configurations providing decreased losses at the three lowest Reynolds numbers and three of the five configurations providing decreased losses at the highest Reynolds number. The primary mechanisms that provide these manipulations include: suppression of the vortex-pairing phenomenon, which reduces both the shear-layer thickness and the levels of small-scale turbulence; the promotion of smaller-scale turbulence, resulting from the disturbances generated upstream of separation, which provides quicker transition and shorter separation bubbles; the elimination of the separation bubble with transition occurring in an attached boundary layer; and physical disturbance, downstream of separation, of the growing instability waves to manipulate the vortical structures and cause quicker reattachment. DEWEY : 620.1 ISSN : 0098-2202

PIV-POD investigation of the wake of a sharp-edged flat bluff body immersed in a shallow channel flow / Arindam Singha in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 12 p. Titre : PIV-POD investigation of the wake of a sharp-edged flat bluff body immersed in a shallow channel flow Type de document : texte imprimé Auteurs : Arindam Singha, Auteur ; A.-M. Shinneeb, Auteur ; Ram Balachandar, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence;  wakes;  channel  flow;  vortices Résumé : This paper reports particle-image velocimetry measurements of instantaneous velocity fields in the wake of a sharp-edged bluff body immersed vertically in a shallow smooth open channel flow. The maximum flow velocity was 0.19 m/s and the Reynolds number based on the water depth was 18,270. The purpose of the present study is to show the vertical variation of the velocity field in the near region of a shallow wake. Measurements of the flow field in the vertical central plane and in the horizontal near-bed, mid-depth, and near-surface planes were taken. Then, the mean flow quantities such as the mean velocity, turbulence intensity, and Reynolds stress fields were investigated. In addition, the proper orthogonal decomposition technique was used to reconstruct the velocity fields to investigate the energetic vortical structures. The results showed that the largest recirculation zone in the mean velocity fields occurred in the mid-depth velocity field, while the smallest one occurred near the bed. Also, the fluid was entrained from the sides toward the wake central plane in the three horizontal velocity fields but with different rates. This behavior was attributed to the existence of quasi-streamwise vortices near the boundaries. In addition, patterns of ejection and sweep events near the free surface similar to the features commonly observed near the wall-bounded flows were observed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] PIV-POD investigation of the wake of a sharp-edged flat bluff body immersed in a shallow channel flow [texte imprimé] / Arindam Singha, Auteur ; A.-M. Shinneeb, Auteur ; Ram Balachandar, Auteur . - 2009 . - 12 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 12 p. Mots-clés : flow  (dynamics);  turbulence;  wakes;  channel  flow;  vortices Résumé : This paper reports particle-image velocimetry measurements of instantaneous velocity fields in the wake of a sharp-edged bluff body immersed vertically in a shallow smooth open channel flow. The maximum flow velocity was 0.19 m/s and the Reynolds number based on the water depth was 18,270. The purpose of the present study is to show the vertical variation of the velocity field in the near region of a shallow wake. Measurements of the flow field in the vertical central plane and in the horizontal near-bed, mid-depth, and near-surface planes were taken. Then, the mean flow quantities such as the mean velocity, turbulence intensity, and Reynolds stress fields were investigated. In addition, the proper orthogonal decomposition technique was used to reconstruct the velocity fields to investigate the energetic vortical structures. The results showed that the largest recirculation zone in the mean velocity fields occurred in the mid-depth velocity field, while the smallest one occurred near the bed. Also, the fluid was entrained from the sides toward the wake central plane in the three horizontal velocity fields but with different rates. This behavior was attributed to the existence of quasi-streamwise vortices near the boundaries. In addition, patterns of ejection and sweep events near the free surface similar to the features commonly observed near the wall-bounded flows were observed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Quasi-1D unsteady conjugate module for rocket engine and propulsion system simulations / Bryan T. Campbell in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Titre : Quasi-1D unsteady conjugate module for rocket engine and propulsion system simulations Type de document : texte imprimé Auteurs : Bryan T. Campbell, Auteur ; Roger L. Davis, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pressure;  flow  (dynamics);  heat  transfer;  fluids;  engineering  simulation;  pipes;  propulsion  systems;  equations;  nitrogen;  rocket  engines;  steady  state;  water Résumé : A new quasi-one-dimensional procedure (one-dimensional with area change) is presented for the transient solution of real-fluid flows in lines and volumes including heat transfer effects. The solver will be integrated into a larger suite of software modules developed for simulating rocket engines and propulsion systems. The solution procedure is coupled with a state-of-the-art real-fluid property database so that both compressible and incompressible fluids may be considered using the same procedure. The numerical techniques used in this procedure are described. Test cases modeling transient flow of nitrogen, water, and hydrogen are presented to demonstrate the capability of the current technique. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Quasi-1D unsteady conjugate module for rocket engine and propulsion system simulations [texte imprimé] / Bryan T. Campbell, Auteur ; Roger L. Davis, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Mots-clés : pressure;  flow  (dynamics);  heat  transfer;  fluids;  engineering  simulation;  pipes;  propulsion  systems;  equations;  nitrogen;  rocket  engines;  steady  state;  water Résumé : A new quasi-one-dimensional procedure (one-dimensional with area change) is presented for the transient solution of real-fluid flows in lines and volumes including heat transfer effects. The solver will be integrated into a larger suite of software modules developed for simulating rocket engines and propulsion systems. The solution procedure is coupled with a state-of-the-art real-fluid property database so that both compressible and incompressible fluids may be considered using the same procedure. The numerical techniques used in this procedure are described. Test cases modeling transient flow of nitrogen, water, and hydrogen are presented to demonstrate the capability of the current technique. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Motion of a single newtonian liquid drop through quiescent immiscible visco-elastic liquid / Ritu Gupta in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 11 p. Titre : Motion of a single newtonian liquid drop through quiescent immiscible visco-elastic liquid : shape and eccentricity Type de document : texte imprimé Auteurs : Ritu Gupta, Auteur ; R. K. Wanchoo, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : fluids;  drops;  shapes Résumé : The shape of a single Newtonian liquid drop moving freely under gravity in quiescent non-Newtonian liquid (visco-inelastic and visco-elastic) has been studied. Strong effect of fluid elasticity on the shape of Newtonian liquid drop has been observed. Based on experimental observations, a shape regime graph has been suitably modified for elastic fluids. Correlations have also been proposed for the prediction of eccentricity of the Newtonian liquid drop moving through a non-Newtonian visco-elastic liquid. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Motion of a single newtonian liquid drop through quiescent immiscible visco-elastic liquid : shape and eccentricity [texte imprimé] / Ritu Gupta, Auteur ; R. K. Wanchoo, Auteur . - 2009 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 11 p. Mots-clés : fluids;  drops;  shapes Résumé : The shape of a single Newtonian liquid drop moving freely under gravity in quiescent non-Newtonian liquid (visco-inelastic and visco-elastic) has been studied. Strong effect of fluid elasticity on the shape of Newtonian liquid drop has been observed. Based on experimental observations, a shape regime graph has been suitably modified for elastic fluids. Correlations have also been proposed for the prediction of eccentricity of the Newtonian liquid drop moving through a non-Newtonian visco-elastic liquid. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Axial Development of Flow Regime in Adiabatic Upward Two-Phase Flow in a vertical annulus / J. Enrique Julia in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 11 p. Titre : Axial Development of Flow Regime in Adiabatic Upward Two-Phase Flow in a vertical annulus Type de document : texte imprimé Auteurs : J. Enrique Julia, Auteur ; Basar Ozar, Auteur ; Abhinav Dixit, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  annulus Résumé : This study has investigated the axial development of flow regime of adiabatic upward air-water two-phase flow in a vertical annulus. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The hydraulic diameter of the flow channel, DH, is 19.0 mm and the total length is 4.37 m. The flow regime map includes 72 flow conditions within a range of 0.01 m/s<⟨jg⟩<30 m/s and 0.2 m/s<⟨jf⟩<3.5 m/s, where ⟨jg⟩ and ⟨jf⟩ are, respectively, superficial gas and liquid velocities. The flow regime has been classified into four categories: bubbly, cap-slug, churn, and annular flows. In order to study the axial development of flow regime, area-averaged void fraction measurements have been performed using impedance void meters at three axial positions corresponding to z/DH=52, 149, and 230 simultaneously, where z represents the axial position. The flow regime indicator has been chosen to be statistical parameters from the probability distribution function of the area-averaged void fraction signals from the impedance meters, and self-organized neural networks have been used as the mapping system. This information has been used to analyze the axial development of flow regime as well as to check the predictions given by the existing flow regime transition models. The axial development of flow regime is quantified using the superficial gas velocity and void fraction values where the flow regime transition takes place. The predictions of the models are compared for each flow regime transition. In the current test conditions, the axial development of flow regime occurs in the bubbly to cap-slug (low superficial liquid velocities) and cap-slug to churn (high superficial liquid velocities) flow regime transition zones. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Axial Development of Flow Regime in Adiabatic Upward Two-Phase Flow in a vertical annulus [texte imprimé] / J. Enrique Julia, Auteur ; Basar Ozar, Auteur ; Abhinav Dixit, Auteur . - 2009 . - 11 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 11 p. Mots-clés : flow  (dynamics);  annulus Résumé : This study has investigated the axial development of flow regime of adiabatic upward air-water two-phase flow in a vertical annulus. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The hydraulic diameter of the flow channel, DH, is 19.0 mm and the total length is 4.37 m. The flow regime map includes 72 flow conditions within a range of 0.01 m/s<⟨jg⟩<30 m/s and 0.2 m/s<⟨jf⟩<3.5 m/s, where ⟨jg⟩ and ⟨jf⟩ are, respectively, superficial gas and liquid velocities. The flow regime has been classified into four categories: bubbly, cap-slug, churn, and annular flows. In order to study the axial development of flow regime, area-averaged void fraction measurements have been performed using impedance void meters at three axial positions corresponding to z/DH=52, 149, and 230 simultaneously, where z represents the axial position. The flow regime indicator has been chosen to be statistical parameters from the probability distribution function of the area-averaged void fraction signals from the impedance meters, and self-organized neural networks have been used as the mapping system. This information has been used to analyze the axial development of flow regime as well as to check the predictions given by the existing flow regime transition models. The axial development of flow regime is quantified using the superficial gas velocity and void fraction values where the flow regime transition takes place. The predictions of the models are compared for each flow regime transition. In the current test conditions, the axial development of flow regime occurs in the bubbly to cap-slug (low superficial liquid velocities) and cap-slug to churn (high superficial liquid velocities) flow regime transition zones. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Incubation time and cavitation erosion rate of work-hardening materials / Jean-Pierre Franc in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 14 p. Titre : Incubation time and cavitation erosion rate of work-hardening materials Type de document : texte imprimé Auteurs : Jean-Pierre Franc, Auteur Année de publication : 2009 Article en page(s) : 14 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  surfaces  (materials);  stress;  cavitation;  bubbles;  cavitation  erosion;  erosion;  collapse;  equations;  stainless  steel;  steady  state;  tensile  strength;  thickness;  work  hardening Résumé : A phenomenological analysis of the cavitation erosion process of ductile materials is proposed. On the material side, the main parameters are the thickness of the hardened layer together with the conventional yield strength and ultimate strength. On the fluid side, the erosive potential of the cavitating flow is described in a simplified way using three integral parameters: rate, mean amplitude, and mean size of hydrodynamic impact loads. Explicit equations are derived for the computation of the incubation time and the steady-state erosion rate. They point out two characteristic scales. The time scale, which is relevant to the erosion phenomenon, is the covering time—the time necessary for the impacts to cover the material surface—whereas the pertinent length scale for ductile materials is the thickness of the hardened layer. The incubation time is proportional to the covering time with a multiplicative factor, which strongly depends on flow aggressiveness in terms of the mean amplitude of impact loads. As for the erosion rate under steady-state conditions, it is scaled by the ratio of the thickness of hardened layers to the covering time with an additional dependence on flow aggressiveness, too. The approach is supported by erosion tests conducted in a cavitation tunnel at a velocity of 65 m/s on stainless steel 316 L. Flow aggressiveness is inferred from pitting tests. The same model of material response that was used for mass loss prediction is applied to derive the original hydrodynamic impact loads due to bubble collapses from the geometric features of the pits. Long duration tests are performed in order to determine experimentally the incubation time and the mean depth of penetration rate and to validate the theoretical approach. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Incubation time and cavitation erosion rate of work-hardening materials [texte imprimé] / Jean-Pierre Franc, Auteur . - 2009 . - 14 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 14 p. Mots-clés : flow  (dynamics);  surfaces  (materials);  stress;  cavitation;  bubbles;  cavitation  erosion;  erosion;  collapse;  equations;  stainless  steel;  steady  state;  tensile  strength;  thickness;  work  hardening Résumé : A phenomenological analysis of the cavitation erosion process of ductile materials is proposed. On the material side, the main parameters are the thickness of the hardened layer together with the conventional yield strength and ultimate strength. On the fluid side, the erosive potential of the cavitating flow is described in a simplified way using three integral parameters: rate, mean amplitude, and mean size of hydrodynamic impact loads. Explicit equations are derived for the computation of the incubation time and the steady-state erosion rate. They point out two characteristic scales. The time scale, which is relevant to the erosion phenomenon, is the covering time—the time necessary for the impacts to cover the material surface—whereas the pertinent length scale for ductile materials is the thickness of the hardened layer. The incubation time is proportional to the covering time with a multiplicative factor, which strongly depends on flow aggressiveness in terms of the mean amplitude of impact loads. As for the erosion rate under steady-state conditions, it is scaled by the ratio of the thickness of hardened layers to the covering time with an additional dependence on flow aggressiveness, too. The approach is supported by erosion tests conducted in a cavitation tunnel at a velocity of 65 m/s on stainless steel 316 L. Flow aggressiveness is inferred from pitting tests. The same model of material response that was used for mass loss prediction is applied to derive the original hydrodynamic impact loads due to bubble collapses from the geometric features of the pits. Long duration tests are performed in order to determine experimentally the incubation time and the mean depth of penetration rate and to validate the theoretical approach. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Thermal effect at the incipient stage of cavitation erosion on a stainless steel in ultrasonic vibration cavitation / Haosheng, Chen in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 03 p. Titre : Thermal effect at the incipient stage of cavitation erosion on a stainless steel in ultrasonic vibration cavitation Type de document : texte imprimé Auteurs : Haosheng, Chen, Auteur ; Li Jiang, Auteur ; Liu Shihan, Auteur Année de publication : 2009 Article en page(s) : 03 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : heat;  temperature;  surface  roughness;  cavitation;  bubbles;  temperature  effects;  cavitation  erosion;  erosion;  vibration;  stainless  steel;  water;  high  temperature Résumé : An ultrasonic vibration cavitation erosion experiment was performed to study the thermal effect during the erosion process. The ring affected zone was observed on the sample surface around the erosion pit at the incipient stage of the cavitation erosion. The results of the surface testing on roughness, hardness, and chemical composition proved that the zone was caused by thermal effect, and that the zone surface experienced a tempering process with the temperature higher than 300°C. Numerical simulation results show that the high temperature domain in the bubble directly contacting the solid wall is a necessary condition for the occurrence of the tempering process on the zone surface, or the heat in the bubble can hardly be transferred to the solid wall under the effects of the great temperature gradient in the bubble and the quick cooling process in the water. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Thermal effect at the incipient stage of cavitation erosion on a stainless steel in ultrasonic vibration cavitation [texte imprimé] / Haosheng, Chen, Auteur ; Li Jiang, Auteur ; Liu Shihan, Auteur . - 2009 . - 03 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 03 p. Mots-clés : heat;  temperature;  surface  roughness;  cavitation;  bubbles;  temperature  effects;  cavitation  erosion;  erosion;  vibration;  stainless  steel;  water;  high  temperature Résumé : An ultrasonic vibration cavitation erosion experiment was performed to study the thermal effect during the erosion process. The ring affected zone was observed on the sample surface around the erosion pit at the incipient stage of the cavitation erosion. The results of the surface testing on roughness, hardness, and chemical composition proved that the zone was caused by thermal effect, and that the zone surface experienced a tempering process with the temperature higher than 300°C. Numerical simulation results show that the high temperature domain in the bubble directly contacting the solid wall is a necessary condition for the occurrence of the tempering process on the zone surface, or the heat in the bubble can hardly be transferred to the solid wall under the effects of the great temperature gradient in the bubble and the quick cooling process in the water. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

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