Documents disponibles écrits par cet auteur

Entropy generation in a boundary layer transitioning under the influence of freestream turbulence / Edmond J. Walsh in Transactions of the ASME . Journal of fluids engineering, Vol. 133 N° 6 (Juin 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 6 (Juin 2011) . - 10 p. Titre : Entropy generation in a boundary layer transitioning under the influence of freestream turbulence Type de document : texte imprimé Auteurs : Edmond J. Walsh, Auteur ; Mc Eligot, Donald M., Auteur ; Brandt, Luca, Auteur Année de publication : 2011 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Boundary  layer  turbulence  Convection  Entropy  Flow  simulation  Laminar  flow  Laminar  to  turbulent  transitions  Numerical  analysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The objective of the present research is to develop new fundamental knowledge of the entropy generation process in laminar flow with significant fluctuations (called pre-transition) and during transition prematurely induced by strong freestream turbulence (bypass transition). Results of direct numerical simulations are employed. In the pre-transitional boundary layer, the perturbations by the streaky structures modify the mean velocity profile and induce a “quasi-turbulent” contribution to indirect dissipation. Application of classical laminar theory leads to underprediction of the entropy generated. In the transition region the pointwise entropy generation rate (S[prime][prime][prime])+ initially increases near the wall and then decreases to correspond to the distribution predicted for a fully-turbulent boundary layer as the flow progresses downstream. In contrast to a developed turbulent flow, the term for turbulent convection in the turbulence kinetic energy balance is significant and can play an important role in some regions of the transitioning boundary layer. More turbulent energy is produced than dissipated and the excess is convected downstream as the boundary layer grows. Since it is difficult to measure and predict true turbulent dissipation rates (and hence, entropy generation rates) exactly other than by expensive direct numerical simulations, a motivation for this research is to evaluate approximate methods for possible use in experiments and design. These new results demonstrate that an approximate technique, used by many investigators, overestimates the dissipation coefficient Cd by up to seventeen per cent. For better predictions and measurements, an integral approach accounting for the important turbulent energy flux is proposed and validated for the case studied. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...] [article] Entropy generation in a boundary layer transitioning under the influence of freestream turbulence [texte imprimé] / Edmond J. Walsh, Auteur ; Mc Eligot, Donald M., Auteur ; Brandt, Luca, Auteur . - 2011 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 6 (Juin 2011) . - 10 p. Mots-clés : Boundary  layer  turbulence  Convection  Entropy  Flow  simulation  Laminar  flow  Laminar  to  turbulent  transitions  Numerical  analysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The objective of the present research is to develop new fundamental knowledge of the entropy generation process in laminar flow with significant fluctuations (called pre-transition) and during transition prematurely induced by strong freestream turbulence (bypass transition). Results of direct numerical simulations are employed. In the pre-transitional boundary layer, the perturbations by the streaky structures modify the mean velocity profile and induce a “quasi-turbulent” contribution to indirect dissipation. Application of classical laminar theory leads to underprediction of the entropy generated. In the transition region the pointwise entropy generation rate (S[prime][prime][prime])+ initially increases near the wall and then decreases to correspond to the distribution predicted for a fully-turbulent boundary layer as the flow progresses downstream. In contrast to a developed turbulent flow, the term for turbulent convection in the turbulence kinetic energy balance is significant and can play an important role in some regions of the transitioning boundary layer. More turbulent energy is produced than dissipated and the excess is convected downstream as the boundary layer grows. Since it is difficult to measure and predict true turbulent dissipation rates (and hence, entropy generation rates) exactly other than by expensive direct numerical simulations, a motivation for this research is to evaluate approximate methods for possible use in experiments and design. These new results demonstrate that an approximate technique, used by many investigators, overestimates the dissipation coefficient Cd by up to seventeen per cent. For better predictions and measurements, an integral approach accounting for the important turbulent energy flux is proposed and validated for the case studied. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...]

Entropy generation in the viscous parts of turbulent boundary layers / Mc Eligot, Donald M. in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 6 (Juin 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p. Titre : Entropy generation in the viscous parts of turbulent boundary layers Type de document : texte imprimé Auteurs : Mc Eligot, Donald M., Auteur ; Edmond J. Walsh, Auteur ; Eckart Laurien, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Pointwise  entropy;  turbulent  boundary  layers Résumé : The local (pointwise) entropy generation rate per unit volume S‴ is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S‴ differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area Sap″, agrees within 5% at its edge. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] [article] Entropy generation in the viscous parts of turbulent boundary layers [texte imprimé] / Mc Eligot, Donald M., Auteur ; Edmond J. Walsh, Auteur ; Eckart Laurien, Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 12 p. Mots-clés : Pointwise  entropy;  turbulent  boundary  layers Résumé : The local (pointwise) entropy generation rate per unit volume S‴ is a key to improving many energy processes and applications. Consequently, in the present study, the objectives are to examine the effects of Reynolds number and favorable streamwise pressure gradients on entropy generation rates across turbulent boundary layers on flat plates and—secondarily—to assess a popular approximate technique for their evaluation. About two-thirds or more of the entropy generation occurs in the viscous part, known as the viscous layer. Fundamental new results for entropy generation in turbulent boundary layers are provided by extending available direct numerical simulations. It was found that, with negligible pressure gradients, results presented in wall coordinates are predicted to be near “universal” in the viscous layer. This apparent universality disappears when a significant pressure gradient is applied; increasing the pressure gradient decreases the entropy generation rate. Within the viscous layer, the approximate evaluation of S‴ differs significantly from the “proper” value but its integral, the entropy generation rate per unit surface area Sap″, agrees within 5% at its edge. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]

Measurement of flow phenomena in a lower plenum model of a prismatic gas-cooled reactor / Hugh M. McIlroy, Jr. in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 132 N° 2 (Fevrier 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 2 (Fevrier 2010) . - 07 p. Titre : Measurement of flow phenomena in a lower plenum model of a prismatic gas-cooled reactor Type de document : texte imprimé Auteurs : Hugh M. McIlroy, Jr., Auteur ; Mc Eligot, Donald M., Auteur ; Robert J. Pink, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Chemical  reactors  Confined  flow  Flow  measurement  Jets  Refractive  index  Turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Mean-velocity-field and turbulence data are presented that measure turbulent flow phenomena in an approximately 1:7 scale model of a region of the lower plenum of a typical prismatic gas-cooled reactor similar to a General Atomics gas-turbine-modular helium reactor design. The data were obtained in the Matched-Index-of-Refraction (MIR) Facility at Idaho National Laboratory (INL) and are offered for assessing computational fluid dynamics software. This experiment has been selected as the first standard problem endorsed by the Generation IV International Forum. Results concentrate on the region of the lower plenum near its far reflector wall (away from the outlet duct). The flow in the lower plenum consists of multiple jets injected into a confined cross flow—with obstructions. The model consists of a row of full circular posts along its centerline with half-posts on the two parallel walls to approximate geometry scaled to that expected from the staggered parallel rows of posts in the reactor design. The model is fabricated from clear, fused quartz to match the refractive-index of the working fluid so that optical techniques may be employed for the measurements. The benefit of the MIR technique is that it permits optical measurements to determine flow characteristics in complex passages in and around objects to be obtained without locating intrusive transducers that will disturb the flow field and without distortion of the optical paths. An advantage of the INL system is its large size, leading to improved spatial and temporal resolutions compared with similar facilities at smaller scales. A three-dimensional particle image velocimetry system was used to collect the data. Inlet-jet Reynolds numbers (based on the jet diameter and the time-mean bulk velocity) are approximately 4300 and 12,400. Uncertainty analyses and a discussion of the standard problem are included. The measurements reveal developing, nonuniform, turbulent flow in the inlet jets and complicated flow patterns in the model lower plenum. Data include three-dimensional vector plots, data displays along the coordinate planes (slices), and presentations that describe the component flows at specific regions in the model. Information on inlet conditions is also presented. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000002 [...] [article] Measurement of flow phenomena in a lower plenum model of a prismatic gas-cooled reactor [texte imprimé] / Hugh M. McIlroy, Jr., Auteur ; Mc Eligot, Donald M., Auteur ; Robert J. Pink, Auteur . - 2010 . - 07 p. Génie Mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 132 N° 2 (Fevrier 2010) . - 07 p. Mots-clés : Chemical  reactors  Confined  flow  Flow  measurement  Jets  Refractive  index  Turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Mean-velocity-field and turbulence data are presented that measure turbulent flow phenomena in an approximately 1:7 scale model of a region of the lower plenum of a typical prismatic gas-cooled reactor similar to a General Atomics gas-turbine-modular helium reactor design. The data were obtained in the Matched-Index-of-Refraction (MIR) Facility at Idaho National Laboratory (INL) and are offered for assessing computational fluid dynamics software. This experiment has been selected as the first standard problem endorsed by the Generation IV International Forum. Results concentrate on the region of the lower plenum near its far reflector wall (away from the outlet duct). The flow in the lower plenum consists of multiple jets injected into a confined cross flow—with obstructions. The model consists of a row of full circular posts along its centerline with half-posts on the two parallel walls to approximate geometry scaled to that expected from the staggered parallel rows of posts in the reactor design. The model is fabricated from clear, fused quartz to match the refractive-index of the working fluid so that optical techniques may be employed for the measurements. The benefit of the MIR technique is that it permits optical measurements to determine flow characteristics in complex passages in and around objects to be obtained without locating intrusive transducers that will disturb the flow field and without distortion of the optical paths. An advantage of the INL system is its large size, leading to improved spatial and temporal resolutions compared with similar facilities at smaller scales. A three-dimensional particle image velocimetry system was used to collect the data. Inlet-jet Reynolds numbers (based on the jet diameter and the time-mean bulk velocity) are approximately 4300 and 12,400. Uncertainty analyses and a discussion of the standard problem are included. The measurements reveal developing, nonuniform, turbulent flow in the inlet jets and complicated flow patterns in the model lower plenum. Data include three-dimensional vector plots, data displays along the coordinate planes (slices), and presentations that describe the component flows at specific regions in the model. Information on inlet conditions is also presented. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000132000002 [...]