Documents disponibles écrits par cet auteur

Influence of upstream conditions and gravity on highly inertial thin-film flow / Roger E. Khayat 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) . - 13 p. Titre : Influence of upstream conditions and gravity on highly inertial thin-film flow Type de document : texte imprimé Auteurs : Roger E. Khayat, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : thin-film  flow;  Newtonian  fluid Résumé : Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...] [article] Influence of upstream conditions and gravity on highly inertial thin-film flow [texte imprimé] / Roger E. Khayat, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 6 (Juin 2008) . - 13 p. Mots-clés : thin-film  flow;  Newtonian  fluid Résumé : Steady two-dimensional thin-film flow of a Newtonian fluid is examined in this theoretical study. The influence of exit conditions and gravity is examined in detail. The considered flow is of moderately high inertia. The flow is dictated by the thin-film equations of boundary layer type, which are solved by expanding the flow field in orthonormal modes in the transverse direction and using Galerkin projection method, combined with integration along the flow direction. Three types of exit conditions are investigated, namely, parabolic, semiparabolic, and uniform flow. It is found that the type of exit conditions has a significant effect on the development of the free surface and flow field near the exit. While for the parabolic velocity profile at the exit, the free surface exhibits a local depression, for semiparabolic and uniform velocity profiles, the height of the film increases monotonically with streamwise position. In order to examine the influence of gravity, the flow is studied down a vertical wall as well as over a horizontal wall. The role of gravity is different for the two types of wall orientation. It is found that for the horizontal wall, a hydraulic-jump-like structure is formed and the flow further downstream exhibits a shock. The influence of exit conditions on shock formation is examined in detail. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27318 [...]

Interplay between inertia and elasticity in film casting / Radoslav German in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 8 (Août 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 8 (Août 2008) . - 12 p. Titre : Interplay between inertia and elasticity in film casting Type de document : texte imprimé Auteurs : Radoslav German, Auteur ; Roger E. Khayat, Auteur Année de publication : 2009 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Inertia  (mechanics);  stability;  flow  (dynamics);  elasticity;  fluids;  stress;  boundary-value  problems;  steady  state;  film  casting;  equations;  polymers;  fibers;  spin  (aerodynamics);  elongation Résumé : The influence of inertia and boundary conditions on the steady state and stability of isothermal film casting of viscoelastic fluids is examined using a Phan-Thien–Tanner rheological model. The elongational flow between the die exit and the take-up point is investigated. In general, the steady-state film tends to contract for low-inertia flow; this contraction, however, is significantly diminished by inertia. The polymeric normal stresses and primary normal stress difference decrease in the most of the air gap as inertia increases. In contrast, the stress and stress difference increase considerably near the take-up point due to a dramatic increase in the elongation rate. The linear stability analysis for two-dimensional disturbances is carried out. For a polymer with no degradation, and in the absence of inertia (Re=0), the analysis predicts critical draw ratios that form an envelope to an unstable region. This region of unstable conditions reduces as inertia increases. Two branches of neutral stability curve are observed for higher-inertia flow as opposed to a single curve for Re=0. The unstable region expands as α increases, where α is a measure of polymer degradation. When α becomes sufficiently large, the elasticity tends to destabilize the flow. It is also found that boundary conditions have an important influence on the steady-state profiles and stability region, particularly for high-elasticity fluids. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Interplay between inertia and elasticity in film casting [texte imprimé] / Radoslav German, Auteur ; Roger E. Khayat, Auteur . - 2009 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 8 (Août 2008) . - 12 p. Mots-clés : Inertia  (mechanics);  stability;  flow  (dynamics);  elasticity;  fluids;  stress;  boundary-value  problems;  steady  state;  film  casting;  equations;  polymers;  fibers;  spin  (aerodynamics);  elongation Résumé : The influence of inertia and boundary conditions on the steady state and stability of isothermal film casting of viscoelastic fluids is examined using a Phan-Thien–Tanner rheological model. The elongational flow between the die exit and the take-up point is investigated. In general, the steady-state film tends to contract for low-inertia flow; this contraction, however, is significantly diminished by inertia. The polymeric normal stresses and primary normal stress difference decrease in the most of the air gap as inertia increases. In contrast, the stress and stress difference increase considerably near the take-up point due to a dramatic increase in the elongation rate. The linear stability analysis for two-dimensional disturbances is carried out. For a polymer with no degradation, and in the absence of inertia (Re=0), the analysis predicts critical draw ratios that form an envelope to an unstable region. This region of unstable conditions reduces as inertia increases. Two branches of neutral stability curve are observed for higher-inertia flow as opposed to a single curve for Re=0. The unstable region expands as α increases, where α is a measure of polymer degradation. When α becomes sufficiently large, the elasticity tends to destabilize the flow. It is also found that boundary conditions have an important influence on the steady-state profiles and stability region, particularly for high-elasticity fluids. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Linear stability of weakly forced Taylor-vortex flow / Roger E. Khayat in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 5 (Mai 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 3 p. Titre : Linear stability of weakly forced Taylor-vortex flow Type de document : texte imprimé Auteurs : Roger E. Khayat, Auteur Année de publication : 2009 Article en page(s) : 3 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Stability;  flow  (dynamics);  waves;  vortices;  cylinders Résumé : Linear stability analysis of fully developed axisymmetric steady spatially modulated Taylor–Couette flow (TCF) is carried out in the narrow-gap limit. In contrast to unforced TCF, only the vortical base flow is possible in the forced case. It is found that the forcing tends to generally destabilize the base flow, especially around the critical point corresponding to unforced flow. Both the critical Taylor number and wave number are found to essentially linearly decrease with modulation amplitude. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Linear stability of weakly forced Taylor-vortex flow [texte imprimé] / Roger E. Khayat, Auteur . - 2009 . - 3 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 5 (Mai 2008) . - 3 p. Mots-clés : Stability;  flow  (dynamics);  waves;  vortices;  cylinders Résumé : Linear stability analysis of fully developed axisymmetric steady spatially modulated Taylor–Couette flow (TCF) is carried out in the narrow-gap limit. In contrast to unforced TCF, only the vortical base flow is possible in the forced case. It is found that the forcing tends to generally destabilize the base flow, especially around the critical point corresponding to unforced flow. Both the critical Taylor number and wave number are found to essentially linearly decrease with modulation amplitude. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]