Dépouillements

Hydrodynamic characterization of a nozzle check valve by numerical simulation / Stefano Sibilla in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 12 p. Titre : Hydrodynamic characterization of a nozzle check valve by numerical simulation Type de document : texte imprimé Auteurs : Stefano Sibilla, Auteur ; Mario Gallati, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  turbulence;  valves;  pressure  drop;  computer  simulation;  nozzles Résumé : The ability to obtain correct estimates of the hydraulic characteristics of a nozzle check valve by finite-volume numerical simulation is discussed. The evaluation of the numerical results is performed by comparison of the computed pressure drops inside the valve with experimental measurements obtained on an industrial check valve. It is shown that, even with high mesh refinement, the obtained result is highly dependent on the choice of the turbulence model. The renormalization group theory (RNG) k-ε model proves to be the more accurate to describe the flow inside the valve, which is characterized by repeated flow decelerations and accelerations and by boundary layer development under adverse pressure gradient. Pressure-drop and flow coefficients computed by adopting the RNG model agree well with the experimental values at different positions of the plug. The opening transient of the valve is also analyzed by an unsteady flow simulation where the motion of the plug is taken into account. The characteristic curve of the valve obtained in steady flow conditions is finally compared with the transient opening characteristic, highlighting a temporary increase in the pressure drop, which occurs because of a large unsteady separation region downstream of the plug. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Hydrodynamic characterization of a nozzle check valve by numerical simulation [texte imprimé] / Stefano Sibilla, Auteur ; Mario Gallati, Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 12 p. Mots-clés : Flow  (Dynamics);  turbulence;  valves;  pressure  drop;  computer  simulation;  nozzles Résumé : The ability to obtain correct estimates of the hydraulic characteristics of a nozzle check valve by finite-volume numerical simulation is discussed. The evaluation of the numerical results is performed by comparison of the computed pressure drops inside the valve with experimental measurements obtained on an industrial check valve. It is shown that, even with high mesh refinement, the obtained result is highly dependent on the choice of the turbulence model. The renormalization group theory (RNG) k-ε model proves to be the more accurate to describe the flow inside the valve, which is characterized by repeated flow decelerations and accelerations and by boundary layer development under adverse pressure gradient. Pressure-drop and flow coefficients computed by adopting the RNG model agree well with the experimental values at different positions of the plug. The opening transient of the valve is also analyzed by an unsteady flow simulation where the motion of the plug is taken into account. The characteristic curve of the valve obtained in steady flow conditions is finally compared with the transient opening characteristic, highlighting a temporary increase in the pressure drop, which occurs because of a large unsteady separation region downstream of the plug. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

The impact of manifold-to-orifice turning angle on sharp-edge orifice flow characteristics in both cavitation and noncavitation turbulent flow regimes / W. H. Nurick in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 10 p. Titre : The impact of manifold-to-orifice turning angle on sharp-edge orifice flow characteristics in both cavitation and noncavitation turbulent flow regimes Type de document : texte imprimé Auteurs : W. H. Nurick, Auteur ; T. Ohanian, Auteur ; D. G. Talley, Auteur Année de publication : 2009 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  turbulence;  avitation;  manifolds;  turning  angles;  equations;  design;  orifices Résumé : The approach taken was to analyze the results in a manner consistent with application by design engineers to new and existing applications, while providing some insight into the processes that are occurring. This paper deals with predicting the initiation of cavitation, cavitation impacts on the contraction coefficient (Cc), as well as noncavitation impacts on discharge coefficient (Cd) from L/D of five sharp-edge orifices over a turning angle range between 60 deg and 120 deg. The results show that in the cavitation regime, Cc is controlled by the cavitation parameter (Kcav), where the data follow the 1∕2 power with Kcav, and inception of cavitation occurs at a Kcav of 1.8. In the noncavitation regime for conditions where the cross velocity is 0 the data are consistent with the first order equation relating head loss (HL) to the dynamic pressure where KL is constant and is consistent with in-line orifices. Cross flow has a significant impact on loss coefficient and depends on both the turning angle and manifold inlet to orifice exit velocity ratio. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] The impact of manifold-to-orifice turning angle on sharp-edge orifice flow characteristics in both cavitation and noncavitation turbulent flow regimes [texte imprimé] / W. H. Nurick, Auteur ; T. Ohanian, Auteur ; D. G. Talley, Auteur . - 2009 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 10 p. Mots-clés : Flow  (Dynamics);  turbulence;  avitation;  manifolds;  turning  angles;  equations;  design;  orifices Résumé : The approach taken was to analyze the results in a manner consistent with application by design engineers to new and existing applications, while providing some insight into the processes that are occurring. This paper deals with predicting the initiation of cavitation, cavitation impacts on the contraction coefficient (Cc), as well as noncavitation impacts on discharge coefficient (Cd) from L/D of five sharp-edge orifices over a turning angle range between 60 deg and 120 deg. The results show that in the cavitation regime, Cc is controlled by the cavitation parameter (Kcav), where the data follow the 1∕2 power with Kcav, and inception of cavitation occurs at a Kcav of 1.8. In the noncavitation regime for conditions where the cross velocity is 0 the data are consistent with the first order equation relating head loss (HL) to the dynamic pressure where KL is constant and is consistent with in-line orifices. Cross flow has a significant impact on loss coefficient and depends on both the turning angle and manifold inlet to orifice exit velocity ratio. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Numerically investigating the effects of cross-links in scaled microchannel heat sinks / Minh Dang in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p. Titre : Numerically investigating the effects of cross-links in scaled microchannel heat sinks Type de document : texte imprimé Auteurs : Minh Dang, Auteur ; Ibrahim Hassan, Auteur ; Sung In Kim, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Two-phase  flow;  heat  sinks;  pressure  drop;  microchannels;  flow  (Dynamics);  channels  (Hydraulic  engineering);  design;  computational  fluid  dynamics Résumé : Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3 . A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Numerically investigating the effects of cross-links in scaled microchannel heat sinks [texte imprimé] / Minh Dang, Auteur ; Ibrahim Hassan, Auteur ; Sung In Kim, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p. Mots-clés : Two-phase  flow;  heat  sinks;  pressure  drop;  microchannels;  flow  (Dynamics);  channels  (Hydraulic  engineering);  design;  computational  fluid  dynamics Résumé : Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3 . A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems / Baratta, Mirko in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p Titre : Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems Type de document : texte imprimé Auteurs : Baratta, Mirko, Auteur ; Andrea Emilio Catania, Auteur ; Alessandro Ferrari, Auteur Année de publication : 2009 Article en page(s) : 13 p Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Oscillations;  pressure;  fuels;  waves;  ejectors;  pipes;  rails;  design Résumé : In multijet common rail (CR) systems, the capability to manage multiple injections with full flexibility in the choice of the dwell time (DT) between consecutive solenoid current pulses is one of the most relevant design targets. Pressure oscillations triggered by the nozzle closure after each injection event induce disturbances in the amount of fuel injected during subsequent injections. This causes a remarkable dispersion in the mass of fuel injected when DT is varied. The effects of the hydraulic circuit layout of CR systems were investigated with the objective to provide design rules for reducing the dependence of the injected fuel amount on DT. A multijet CR of the latest solenoid-type generation was experimentally analyzed at different operating conditions on a high performance test bench. The considerable influence that the injector-supplying pipe dimensions can exert on the frequency and amplitude of the injection-induced pressure oscillations was widely investigated and a physical explanation of cause-effect relationships was found by energetics considerations, starting from experimental tests. A parametric study was performed to identify the best geometrical configurations of the injector-supplying pipe so as to minimize pressure oscillations. The analysis was carried out with the aid of a previously developed simple zero-dimensional model, allowing the evaluation of pressure-wave frequencies as functions of main system geometric data. Pipes of innovative aspect ratio and capable of halving the amplitude of injected-volume fluctuations versus DT were proposed. Purposely designed orifices were introduced into the rail-pipe connectors of a commercial automotive injection system, so as to damp pressure oscillations. Their effects on multiple-injection performance were experimentally determined as being sensible. The resulting reduction in the injector fueling capacity was quantified. It increased by lowering the orifice diameter. The application of the orifice to the injector inlet-pipe with innovative aspect ratio led to a hydraulic circuit solution, which coupled active and passive damping of the pressure waves and minimized the disturbances in injected fuel volumes. Finally, the influence of the rail capacity on pressure-wave dynamics was studied and the possibility of severely reducing the rail volume (up to one-fourth) was assessed. This can lead to a system not only with reduced overall sizes but also with a prompter dynamic response during engine transients. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Hydraulic circuit design rules to remove the dependence of the injected fuel amount on dwell time in multijet CR systems [texte imprimé] / Baratta, Mirko, Auteur ; Andrea Emilio Catania, Auteur ; Alessandro Ferrari, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 13 p Mots-clés : Oscillations;  pressure;  fuels;  waves;  ejectors;  pipes;  rails;  design Résumé : In multijet common rail (CR) systems, the capability to manage multiple injections with full flexibility in the choice of the dwell time (DT) between consecutive solenoid current pulses is one of the most relevant design targets. Pressure oscillations triggered by the nozzle closure after each injection event induce disturbances in the amount of fuel injected during subsequent injections. This causes a remarkable dispersion in the mass of fuel injected when DT is varied. The effects of the hydraulic circuit layout of CR systems were investigated with the objective to provide design rules for reducing the dependence of the injected fuel amount on DT. A multijet CR of the latest solenoid-type generation was experimentally analyzed at different operating conditions on a high performance test bench. The considerable influence that the injector-supplying pipe dimensions can exert on the frequency and amplitude of the injection-induced pressure oscillations was widely investigated and a physical explanation of cause-effect relationships was found by energetics considerations, starting from experimental tests. A parametric study was performed to identify the best geometrical configurations of the injector-supplying pipe so as to minimize pressure oscillations. The analysis was carried out with the aid of a previously developed simple zero-dimensional model, allowing the evaluation of pressure-wave frequencies as functions of main system geometric data. Pipes of innovative aspect ratio and capable of halving the amplitude of injected-volume fluctuations versus DT were proposed. Purposely designed orifices were introduced into the rail-pipe connectors of a commercial automotive injection system, so as to damp pressure oscillations. Their effects on multiple-injection performance were experimentally determined as being sensible. The resulting reduction in the injector fueling capacity was quantified. It increased by lowering the orifice diameter. The application of the orifice to the injector inlet-pipe with innovative aspect ratio led to a hydraulic circuit solution, which coupled active and passive damping of the pressure waves and minimized the disturbances in injected fuel volumes. Finally, the influence of the rail capacity on pressure-wave dynamics was studied and the possibility of severely reducing the rail volume (up to one-fourth) was assessed. This can lead to a system not only with reduced overall sizes but also with a prompter dynamic response during engine transients. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Instabilities of nonreturn valves in low-speed air systems / Mark Potter in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 8 p Titre : Instabilities of nonreturn valves in low-speed air systems Type de document : texte imprimé Auteurs : Mark Potter, Auteur ; Marko Bacic, Auteur ; Phil Ligrani, Auteur Année de publication : 2009 Article en page(s) : 8 p Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  valves;  stability Résumé : Practical observations of the nonreturn valve wear in aero-engine cabin-bleed systems suggest that such valves are subject to unstable behavior. A theoretical model for the prediction of nonreturn valve instabilities in air systems is proposed and a nonlinear state-space model of the nonreturn valve and air volume interaction is derived from first principles. Experimental work is used to identify both the dynamic characteristics and the flow properties of the valve, which are used to identify the coefficients within the model. Through frequency analysis of valve oscillatory behavior, the levels of damping within the system are identified. Finally, using a local linearization of the state-space model an explicit mathematical prediction of valve stability is derived based on system parameters. These predictions are used to generate a map of the transition from stable to unstable system behavior for low-speed air flow, which is in excellent agreement with experimental data. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Instabilities of nonreturn valves in low-speed air systems [texte imprimé] / Mark Potter, Auteur ; Marko Bacic, Auteur ; Phil Ligrani, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 8 p Mots-clés : Flow  (Dynamics);  valves;  stability Résumé : Practical observations of the nonreturn valve wear in aero-engine cabin-bleed systems suggest that such valves are subject to unstable behavior. A theoretical model for the prediction of nonreturn valve instabilities in air systems is proposed and a nonlinear state-space model of the nonreturn valve and air volume interaction is derived from first principles. Experimental work is used to identify both the dynamic characteristics and the flow properties of the valve, which are used to identify the coefficients within the model. Through frequency analysis of valve oscillatory behavior, the levels of damping within the system are identified. Finally, using a local linearization of the state-space model an explicit mathematical prediction of valve stability is derived based on system parameters. These predictions are used to generate a map of the transition from stable to unstable system behavior for low-speed air flow, which is in excellent agreement with experimental data. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Experimental study on the amplitude of a free surface fluctuation / Ho-Yun Nam in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 11 p. Titre : Experimental study on the amplitude of a free surface fluctuation Type de document : texte imprimé Auteurs : Ho-Yun Nam, Auteur ; Byoung-Hae Choi, Auteur ; Jong-Man Kim, Auteur Année de publication : 2009 Article en page(s) : 11 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  nozzles;  errors;  geometry;  vessels;  water Résumé : An experimental study was performed to measure the fluctuation phenomena of a free surface in a vessel with or without an internal structure. A flow enters from the bottom and flows out of the side wall nozzles. Characteristics of the free surface fluctuation are investigated in terms of the geometry factors of the vessel and the flow rate. A modified Froude number is proposed to describe the amplitude of a free surface fluctuation. The fluctuation amplitude increases stably with an increase in the ratio of the vessel diameter to the water level in a vessel without an internal structure. When the ratio is greater than about 2, the fluctuation decreases suddenly with an increase in the ratio and it becomes unstable. The fluctuation amplitude is linearly proportional to the square of the Froude number. The amplitude of a free surface fluctuation increases with an increase in the height of an internal structure, but this increasing ratio is reduced when the height becomes higher. Two correlations were developed in terms of the Froude number and geometry factors to predict the amplitude of the free surface fluctuation in a vessel with or without an internal structure. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Experimental study on the amplitude of a free surface fluctuation [texte imprimé] / Ho-Yun Nam, Auteur ; Byoung-Hae Choi, Auteur ; Jong-Man Kim, Auteur . - 2009 . - 11 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 11 p. Mots-clés : Flow  (Dynamics);  nozzles;  errors;  geometry;  vessels;  water Résumé : An experimental study was performed to measure the fluctuation phenomena of a free surface in a vessel with or without an internal structure. A flow enters from the bottom and flows out of the side wall nozzles. Characteristics of the free surface fluctuation are investigated in terms of the geometry factors of the vessel and the flow rate. A modified Froude number is proposed to describe the amplitude of a free surface fluctuation. The fluctuation amplitude increases stably with an increase in the ratio of the vessel diameter to the water level in a vessel without an internal structure. When the ratio is greater than about 2, the fluctuation decreases suddenly with an increase in the ratio and it becomes unstable. The fluctuation amplitude is linearly proportional to the square of the Froude number. The amplitude of a free surface fluctuation increases with an increase in the height of an internal structure, but this increasing ratio is reduced when the height becomes higher. Two correlations were developed in terms of the Froude number and geometry factors to predict the amplitude of the free surface fluctuation in a vessel with or without an internal structure. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Computational dynamics of a thermally decomposable viscoelastic lubricant under shear / T. Chinyoka in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Titre : Computational dynamics of a thermally decomposable viscoelastic lubricant under shear Type de document : texte imprimé Auteurs : T. Chinyoka, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Dynamics  (Mechanics);  temperature;  fluids;  lubricants;  shear  (Mechanics);  algorithms;  equations;  stress;  viscoelasticity;  delays Résumé : The effect of viscoelasticity on the thermodynamic performance of a thermally decomposable lubricant subjected to shear and Arrhenius kinetics is investigated with direct numerical simulations. A numerical algorithm based on the finite difference method is implemented in time and space with the Oldroyd-B constitutive equation as the model for the viscoelastic liquids. We report enhanced efficiency in the case of a polymeric lubricant as compared with the purely viscous lubricant. In particular, it is demonstrated that the use of polymeric liquids helps to delay the onset of thermal runaway as compared with progressively Newtonian liquids. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Computational dynamics of a thermally decomposable viscoelastic lubricant under shear [texte imprimé] / T. Chinyoka, Auteur . - 2009 . - 7 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Mots-clés : Dynamics  (Mechanics);  temperature;  fluids;  lubricants;  shear  (Mechanics);  algorithms;  equations;  stress;  viscoelasticity;  delays Résumé : The effect of viscoelasticity on the thermodynamic performance of a thermally decomposable lubricant subjected to shear and Arrhenius kinetics is investigated with direct numerical simulations. A numerical algorithm based on the finite difference method is implemented in time and space with the Oldroyd-B constitutive equation as the model for the viscoelastic liquids. We report enhanced efficiency in the case of a polymeric lubricant as compared with the purely viscous lubricant. In particular, it is demonstrated that the use of polymeric liquids helps to delay the onset of thermal runaway as compared with progressively Newtonian liquids. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Experiments and models of the magneto rheological behavior of high weight percent suspensions of carbonyl iron particles in silicone oil / Farzad Ahmadkhanlou in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Titre : Experiments and models of the magneto rheological behavior of high weight percent suspensions of carbonyl iron particles in silicone oil Type de document : texte imprimé Auteurs : Farzad Ahmadkhanlou, Auteur ; Monon, Mahboob, Auteur ; Stephen Bechtel, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Fluids;  particulate  matter;  magnetic  fields;  shear  (Mechanics);  dampers;  stress;  silicones;  weight  (Mass) Résumé : Flow properties of magnetorheological (MR) fluids are greatly altered by the application of a magnetic field. The design, optimization, and control of novel devices that exploit MR fluid behavior in multidegree of freedom applications require three dimensional models characterizing the coupling of magnetic behavior to mechanical behavior in MR fluids. The authors have derived 3D MR fluid models based on multiscale kinetic theory. The underlying bases of the models are summarized, with phenomenological empiricism distinguished from multiscale first principles, and the models’ ability to capture the experimentally measured mechanical response of a MR fluid-based damper to specified magnetic fields is assessed. The results of this comparison are that the kinetic theory-based models both relate macroscale MR fluid behavior to a first-principles description of magnetomechanical coupling at the microscale and possess the flexibility to best match the measured behavior of a particular MR fluid device observed in our experiments. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Experiments and models of the magneto rheological behavior of high weight percent suspensions of carbonyl iron particles in silicone oil [texte imprimé] / Farzad Ahmadkhanlou, Auteur ; Monon, Mahboob, Auteur ; Stephen Bechtel, Auteur . - 2009 . - 7 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Mots-clés : Fluids;  particulate  matter;  magnetic  fields;  shear  (Mechanics);  dampers;  stress;  silicones;  weight  (Mass) Résumé : Flow properties of magnetorheological (MR) fluids are greatly altered by the application of a magnetic field. The design, optimization, and control of novel devices that exploit MR fluid behavior in multidegree of freedom applications require three dimensional models characterizing the coupling of magnetic behavior to mechanical behavior in MR fluids. The authors have derived 3D MR fluid models based on multiscale kinetic theory. The underlying bases of the models are summarized, with phenomenological empiricism distinguished from multiscale first principles, and the models’ ability to capture the experimentally measured mechanical response of a MR fluid-based damper to specified magnetic fields is assessed. The results of this comparison are that the kinetic theory-based models both relate macroscale MR fluid behavior to a first-principles description of magnetomechanical coupling at the microscale and possess the flexibility to best match the measured behavior of a particular MR fluid device observed in our experiments. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

A three-equation Eddy-viscosity model for Reynolds-averaged Navier–stokes simulations of transitional flow / D. Keith Walters in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 14 p. Titre : A three-equation Eddy-viscosity model for Reynolds-averaged Navier–stokes simulations of transitional flow Type de document : texte imprimé Auteurs : D. Keith Walters, Auteur ; Davor Cokljat, Auteur Année de publication : 2009 Article en page(s) : 14 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Flow  (Dynamics);  turbulence;  Eddies  (Fluid  dynamics);  viscosity;  boundary  layers;  equations;  airfoils;  flat  plates;  engineering  simulation Résumé : An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-ω framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] A three-equation Eddy-viscosity model for Reynolds-averaged Navier–stokes simulations of transitional flow [texte imprimé] / D. Keith Walters, Auteur ; Davor Cokljat, Auteur . - 2009 . - 14 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 14 p. Mots-clés : Flow  (Dynamics);  turbulence;  Eddies  (Fluid  dynamics);  viscosity;  boundary  layers;  equations;  airfoils;  flat  plates;  engineering  simulation Résumé : An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-ω framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Instantaneous liquid flow rate measurement utilizing the dynamics of laminar pipe flow / Bernhard Manhartsgruber in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 8 p. Titre : Instantaneous liquid flow rate measurement utilizing the dynamics of laminar pipe flow Type de document : texte imprimé Auteurs : Bernhard Manhartsgruber, Auteur Année de publication : 2009 Article en page(s) : 8 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Dynamics  (Mechanics);  flow  (Dynamics);  pipe  flow;  pipes;  pressure;  speed  of  sound;  signals;  energy  dissipation;  fluids;  uncertainty Résumé : This paper deals with the utilization of the dynamic characteristics of laminar flow in circular pipes for the indirect measurement of flow rates. A discrete-time state space realization of the transmission line dynamics is computed via inverse Laplace transform and an identification and model reduction method based on the singular value decomposition. This dynamic system is used for the computation of the flow rate at one end of a pipe section. Special attention is paid to the identification of the speed of sound and the dimensionless dissipation number of the pipe section, since exact knowledge of these parameters is crucial for the reliability of the measurement results. First, experimental validation results are given in a limited range of operating frequencies between 100 Hz and 2000 Hz. Flow rate variations within ±1.2 l/min have been measured with an uncertainty of ±0.07 l/min at the 95% confidence level. The test fluid was mineral oil. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Instantaneous liquid flow rate measurement utilizing the dynamics of laminar pipe flow [texte imprimé] / Bernhard Manhartsgruber, Auteur . - 2009 . - 8 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 8 p. Mots-clés : Dynamics  (Mechanics);  flow  (Dynamics);  pipe  flow;  pipes;  pressure;  speed  of  sound;  signals;  energy  dissipation;  fluids;  uncertainty Résumé : This paper deals with the utilization of the dynamic characteristics of laminar flow in circular pipes for the indirect measurement of flow rates. A discrete-time state space realization of the transmission line dynamics is computed via inverse Laplace transform and an identification and model reduction method based on the singular value decomposition. This dynamic system is used for the computation of the flow rate at one end of a pipe section. Special attention is paid to the identification of the speed of sound and the dimensionless dissipation number of the pipe section, since exact knowledge of these parameters is crucial for the reliability of the measurement results. First, experimental validation results are given in a limited range of operating frequencies between 100 Hz and 2000 Hz. Flow rate variations within ±1.2 l/min have been measured with an uncertainty of ±0.07 l/min at the 95% confidence level. The test fluid was mineral oil. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

Grid independence via automated unstructured adaptation / Ronald J. Chila in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Titre : Grid independence via automated unstructured adaptation Type de document : texte imprimé Auteurs : Ronald J. Chila, Auteur ; Deborah A. Kaminski, Auteur Année de publication : 2009 Article en page(s) : 7 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Combustion;  channels  (Hydraulic  engineering);  sensors;  foundry  coatings;  computational  fluid  dynamics;  cycles;  errors;  airfoils;  hydrogen;  flow  (Dynamics) Résumé : Grid independence is frequently an overlooked item in computational fluid dynamics (CFD) analyses. Results obtained from grid dependent solutions may prove to be costly, in that engineering design decisions can be made using potentially faulty information. An automated method for grid independence is developed for two-dimensional unstructured wall function grids. Grid independence is achieved via successive levels of adaptive refinement. Adaptive refinement is performed in an automated manner and is based on multiple field variables. Sensors are placed at strategic locations within the flow field, which are determined by examining the CFD solution of a uniform grid. Three cases are examined, the backward-facing step, flow over an asymmetric transonic airfoil, and hydrogen combustion in a channel. Grid independent solutions are obtained for all three cases. Results for each case compare well with experimental data and/or other numerical predictions. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] Grid independence via automated unstructured adaptation [texte imprimé] / Ronald J. Chila, Auteur ; Deborah A. Kaminski, Auteur . - 2009 . - 7 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 7 p. Mots-clés : Combustion;  channels  (Hydraulic  engineering);  sensors;  foundry  coatings;  computational  fluid  dynamics;  cycles;  errors;  airfoils;  hydrogen;  flow  (Dynamics) Résumé : Grid independence is frequently an overlooked item in computational fluid dynamics (CFD) analyses. Results obtained from grid dependent solutions may prove to be costly, in that engineering design decisions can be made using potentially faulty information. An automated method for grid independence is developed for two-dimensional unstructured wall function grids. Grid independence is achieved via successive levels of adaptive refinement. Adaptive refinement is performed in an automated manner and is based on multiple field variables. Sensors are placed at strategic locations within the flow field, which are determined by examining the CFD solution of a uniform grid. Three cases are examined, the backward-facing step, flow over an asymmetric transonic airfoil, and hydrogen combustion in a channel. Grid independent solutions are obtained for all three cases. Results for each case compare well with experimental data and/or other numerical predictions. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

The influence of slip boundary conditions on peristaltic pumping in a rectangular channel / X. Mandviwalla in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 12 (Décembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 5 p. Titre : The influence of slip boundary conditions on peristaltic pumping in a rectangular channel Type de document : texte imprimé Auteurs : X. Mandviwalla, Auteur ; R. Archer, Auteur Année de publication : 2009 Article en page(s) : 5 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Channels  (Hydraulic  engineering);  waves;  Boundary-value  problems;  flow  (Dynamics);  wavelength;  Reynolds  number Résumé : The flow of an incompressible fluid is modeled in a channel of a rectangular cross section with two symmetric peristaltic waves propagating on the top and bottom. A low Reynolds number and a long wavelength are assumed. The effect on pumping of the inclusion of slip boundary conditions on the side walls is investigated. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...] [article] The influence of slip boundary conditions on peristaltic pumping in a rectangular channel [texte imprimé] / X. Mandviwalla, Auteur ; R. Archer, Auteur . - 2009 . - 5 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 12 (Décembre 2008) . - 5 p. Mots-clés : Channels  (Hydraulic  engineering);  waves;  Boundary-value  problems;  flow  (Dynamics);  wavelength;  Reynolds  number Résumé : The flow of an incompressible fluid is modeled in a channel of a rectangular cross section with two symmetric peristaltic waves propagating on the top and bottom. A low Reynolds number and a long wavelength are assumed. The effect on pumping of the inclusion of slip boundary conditions on the side walls is investigated. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27349 [...]

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