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۱3–D Thin Layer Navier–Stokes Solution of Supersonic Turbulent Flow
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، دهم،شماره۱، بهار ، سال
تعداد صفحات: ۱۰

۲New Set of Conservation Equations Based on the Kinetic Theory Applied to Gas Mixture Problems
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، چهاردهم،شماره۵، ۲۰۰۷، سال
تعداد صفحات: ۱۱
In this work, the hydrodynamics of multicomponent ideal gas mixtures have been studied. Starting from kinetic equations, the Eulerian approach is used to derive equations of motion for a multicomponent system, where each component may have a different velocity and kinetic temperature. The equations are based on Grad''s method of moment derived from the kinetic model, in a Relaxation Time Approximation (RTA). Based on this model, a computer code has been developed for numerical computation of compressible flows of a binary gas mixture in generalized curvilinear boundary conforming coordinates. Since these equations are similar to the Navier–Stokes equations for the single fluid systems, the same numerical methods are applied to these new equations. The Roe''s numerical scheme is used to discretize the convective terms of governing fluid flow equations. The prepared algorithm and the computer code are capable of computing and presenting the flow fields of each component of the system separately, as well as the average flow field of the multicomponent gas system as a whole. A comparison between the present code results and those of a more common algorithm based on the mixture theory in a supersonic converging–diverging nozzle provides the validation of the present formulation. Afterwards, a more involved nozzle cooling problem with a binary ideal gas (Helium–Xenon) is chosen to compare the present results with those of the ordinary mixture theory. The present model provides the details of the flow fields of each component separately which is not available otherwise.

۳Experimental investigation of bounce phenomenon
نویسنده(ها): ، ، ،
اطلاعات انتشار: Scientia Iranica، هجدهم،شماره۳، ۲۰۱۱، سال
تعداد صفحات: ۷
Extensive wind tunnel tests were performed on several wing– body–tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose–body vortex.

۴Importance of molecular interaction description on the hydrodynamics of gas mixtures
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، هجدهم،شماره۶، ۲۰۱۱، سال
تعداد صفحات: ۱۰
The aim of this study is to analyze the hydrodynamics of gas mixtures invoking a recently proposed multifluid model. The model consists of a separate equation set for one component species of the system and an equation set for average quantities of the mixture. Thereby, it provides details of the flow fields for each of the constituents separately. The new model also computes transport coefficients from some kinetic relations without the requirement of being input externally. Moreover, it automatically describes diffusion processes excluding the use of any coefficients for ordinary, pressure and thermal diffusion, which are generally required during Navier–Stokes computation of gas mixture flows.In the present paper, the model that was applied with hard–sphere molecules is extended to include more realistic molecular interaction descriptions (i.e. Maxwell repulsive potential and Lennard–Jones 12–6 potential). Moreover, the contribution of external forces is incorporated in the multifluid balance equations. Afterwards, the resulting equations are solved for some gas mixture problems in the context of a converging–diverging nozzle, and the importance of the molecular interaction description on the hydrodynamics of the mixtures is analyzed.

۵Numerical simulation of blood flow in a flexible stenosed abdominal real aorta
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، هجدهم،شماره۶، ۲۰۱۱، سال
تعداد صفحات: ۹
This study concerns an evaluation of pulsatile flow and arterial wall behavior in a real world model of a stenosed abdominal aorta and iliac arteries. Two different geometries of a healthy and severly stenosed abdominal aorta, extracted from CT scan images and simulations of fluid flow and tissue interaction (Fluid Solid Interaction), are carried out. The blood is taken as incompressible, non–Newtonian, and the arterial wall tissue is treated as isotropic, elastic material with uniform mechanical properties. The results of using two models with rigid and flexible walls are presented and compared. The computed pressure at the abdominal aorta for a flexible healthy wall is consistent with measured values in vivo conditions. Results show that the computed pressure is lower by 15% for the flexible model, as compared to the rigid and complaint models. Although results obtained from the FSI study of pulsatile healthy and stenosed models show a similar trend for Wall Shear Stress (WSS) patterns, considerable differences in magnitude exist. It is shown that for the cases presented here, the effects of wall flexibility and actual stenosed geometry on the flow performance of veins are noticeable.

۶Two–fluid analysis of a gas mixing problem
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، بيستم،شماره۱، ۲۰۱۳، سال
تعداد صفحات: ۱۰
The mixing pattern of two parallel gas streams initially separated by a splitter plate is analyzed in this study. A recently proposed, two–fluid model is utilized for simulation of the flow field. The model provides separate balance equations for each component species of the system. As a consequence of the strong resemblance of the two–fluid model to the Navier–Stokes equations, the same numerical methods are applied to these new equations. The computations are undertaken for two–fluid systems; one with particles of about equal masses and another with particles of quite distinct masses, and the corresponding results are compared. This clarifies how the mass disparity of the constituents may affect the establishment of the flow field. The influence of molecular interaction descriptions in the model predictions is also examined by comparing the results of a hard–sphere model, the Maxwell repulsive potential, and the Lennard–Jones 12–6 potential.
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