Documents disponibles écrits par cet auteur

Modeling the effects of system rotation on the turbulent scalar fluxes / B. A. Younis in Journal of heat transfer, Vol. 132 N° 5 (Mai 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 5 (Mai 2010) . - pp. [051703-1/14] Titre : Modeling the effects of system rotation on the turbulent scalar fluxes Type de document : texte imprimé Auteurs : B. A. Younis, Auteur ; B. Weigand, Auteur ; F. Mohr, Auteur Article en page(s) : pp. [051703-1/14] Note générale : Physique Langues : Anglais (eng) Mots-clés : Channel  flow  Flow  simulation  Rotational  flow  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : A proposal for modeling the effects of system rotation on the turbulent scalar fluxes is presented. It is based on extension to rotating frames of an explicit algebraic model derived using tensor-representation theory. The model is formulated to allow for the turbulent scalar fluxes to depend on the details of the turbulence field and on the gradients of both the mean-velocity and the scalar. Such dependence, which is absent from conventional models, is required by the exact equations governing the transport of the scalar fluxes. The model's performance is assessed, both a priori and by actual computations, by comparisons with results from recent direct numerical simulations (DNS) of flows in heated channels rotated about their streamwise, spanwise, and wall-normal axes. To place the new model's performance in context, additional comparisons are made with predictions obtained from three alternative models, namely, the conventional gradient-transport model, a model that is implicit in the scalar fluxes derived by simplification of the modeled transport equations for the scalar fluxes, and a differential scalar-flux transport model. The results show that the present model yields predictions that are substantially in better agreement with the DNS results than the algebraic models, and which are indistinguishable from those obtained with the more complex differential model. However, important differences remain and reasons for these are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&smode=strresults& [...] [article] Modeling the effects of system rotation on the turbulent scalar fluxes [texte imprimé] / B. A. Younis, Auteur ; B. Weigand, Auteur ; F. Mohr, Auteur . - pp. [051703-1/14]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 5 (Mai 2010) . - pp. [051703-1/14] Mots-clés : Channel  flow  Flow  simulation  Rotational  flow  Turbulence Index. décimale : 536 Chaleur. Thermodynamique Résumé : A proposal for modeling the effects of system rotation on the turbulent scalar fluxes is presented. It is based on extension to rotating frames of an explicit algebraic model derived using tensor-representation theory. The model is formulated to allow for the turbulent scalar fluxes to depend on the details of the turbulence field and on the gradients of both the mean-velocity and the scalar. Such dependence, which is absent from conventional models, is required by the exact equations governing the transport of the scalar fluxes. The model's performance is assessed, both a priori and by actual computations, by comparisons with results from recent direct numerical simulations (DNS) of flows in heated channels rotated about their streamwise, spanwise, and wall-normal axes. To place the new model's performance in context, additional comparisons are made with predictions obtained from three alternative models, namely, the conventional gradient-transport model, a model that is implicit in the scalar fluxes derived by simplification of the modeled transport equations for the scalar fluxes, and a differential scalar-flux transport model. The results show that the present model yields predictions that are substantially in better agreement with the DNS results than the algebraic models, and which are indistinguishable from those obtained with the more complex differential model. However, important differences remain and reasons for these are discussed. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&smode=strresults& [...]

Prediction of turbulent heat transfer in rotating and nonrotating channels with wall suction and blowing / B. A. Younis in Journal of heat transfer, Vol. 134 N° 7 (Juillet 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 7 (Juillet 2012) . - 09 p. Titre : Prediction of turbulent heat transfer in rotating and nonrotating channels with wall suction and blowing Type de document : texte imprimé Auteurs : B. A. Younis, Auteur ; B. Weigand, Auteur ; A. Laqua, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : turbulence  modeling;  rotating  flows;  heat-flux  closures Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper reports on the prediction of heat transfer in a fully developed turbulent flow in a straight rotating channel with blowing and suction through opposite walls. The channel is rotated about its spanwise axis; a mode of rotation that amplifies the turbulent activity on one wall and suppresses it on the opposite wall leading to reverse transition at high rotation rates. The present predictions are based on the solution of the Reynolds-averaged forms of the governing equations using a second-order accurate finite-volume formulation. The effects of turbulence on momentum transport were accounted for by using a differential Reynolds-stress transport closure. A number of alternative formulations for the difficult fluctuating pressure–strain correlations term were assessed. These included a high turbulence Reynolds-number formulation that required a “wall-function” to bridge the near-wall region as well as three alternative low Reynolds-number formulations that permitted integration through the viscous sublayer, directly to the walls. The models were assessed by comparisons with experimental data for flows in channels at Reynolds-numbers spanning the range of laminar, transitional, and turbulent regimes. The turbulent heat fluxes were modeled via two very different approaches: one involved the solution of a modeled differential transport equation for each of the three heat-flux components, while in the other, the heat fluxes were obtained from an explicit algebraic model derived from tensor representation theory. The results for rotating channels with wall suction and blowing show that the algebraic model, when properly extended to incorporate the effects of rotation, yields results that are essentially identically to those obtained with the far more complex and computationally intensive heat-flux transport closure. This outcome argues in favor of incorporation of the algebraic model in industry-standard turbomachinery codes. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000007 [...] [article] Prediction of turbulent heat transfer in rotating and nonrotating channels with wall suction and blowing [texte imprimé] / B. A. Younis, Auteur ; B. Weigand, Auteur ; A. Laqua, Auteur . - 2012 . - 09 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 7 (Juillet 2012) . - 09 p. Mots-clés : turbulence  modeling;  rotating  flows;  heat-flux  closures Index. décimale : 536 Chaleur. Thermodynamique Résumé : This paper reports on the prediction of heat transfer in a fully developed turbulent flow in a straight rotating channel with blowing and suction through opposite walls. The channel is rotated about its spanwise axis; a mode of rotation that amplifies the turbulent activity on one wall and suppresses it on the opposite wall leading to reverse transition at high rotation rates. The present predictions are based on the solution of the Reynolds-averaged forms of the governing equations using a second-order accurate finite-volume formulation. The effects of turbulence on momentum transport were accounted for by using a differential Reynolds-stress transport closure. A number of alternative formulations for the difficult fluctuating pressure–strain correlations term were assessed. These included a high turbulence Reynolds-number formulation that required a “wall-function” to bridge the near-wall region as well as three alternative low Reynolds-number formulations that permitted integration through the viscous sublayer, directly to the walls. The models were assessed by comparisons with experimental data for flows in channels at Reynolds-numbers spanning the range of laminar, transitional, and turbulent regimes. The turbulent heat fluxes were modeled via two very different approaches: one involved the solution of a modeled differential transport equation for each of the three heat-flux components, while in the other, the heat fluxes were obtained from an explicit algebraic model derived from tensor representation theory. The results for rotating channels with wall suction and blowing show that the algebraic model, when properly extended to incorporate the effects of rotation, yields results that are essentially identically to those obtained with the far more complex and computationally intensive heat-flux transport closure. This outcome argues in favor of incorporation of the algebraic model in industry-standard turbomachinery codes. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000007 [...]