جستجوی مقالات مرتبط با کلیدواژه « Newtonian » در نشریات گروه « مکانیک »

Renal artery stenosis is a major cause of death and permanent harm to the body. The rigidness of the wall of the arteries is the main cause of atherosclerosis and renal artery stenosis. Therefore, the purpose of this study was to evaluate the effect of vessel wall thickening and renal artery stenosis on the entrance of blood flow through the arterioles of the kidney by using physical modeling, second goal of this study was to evaluate the effect of renal artery stenosis on the characteristics of the flow in the downstream and also to identify areas prone to congestion in the presence of renal artery stenosis. Actual geometry and boundary conditions was used for modeling. In this study, Newtonian and non-Newtonian models was assumed for the viscosity of blood and the results were compared to each other. The effect of mild (30%), moderate (50%) and severe (70%) occlusions was studied on the flow parameters. The areas which were prone to congestion were identified in occluded and non-occluded geometries and the results were compared. The results show that not much difference between Newtonian and non-Newtonian models for blood viscosity is noticed in the present geometry and blood can be considered as a Newtonian fluid. Investigation showed that the congestion-prone areas are located before and also in the first branch of bifurcation because in these areas the shear stress is maximum. The congestions haven’t influenced areas which were prone to occlusion, but the more percentage of stenosis the more there is possibility for occlusion.

Numerical study of the effect of stenosis on the hemodynamic parameters in branch of LAD coronary using 0D/3D coupling ˜یÏå [English]
Stenosis in coronary artery and the other cardiac diseases such as Atherosclerosis is major cause of death in the world. Numerical simulation of blood flow can help medical evaluation to curve arteries have been stenosis. The purpose of this paper is to find the effect of arteries stenosis on the hemodynamic parameters by simulation of blood flow in LAD branch of coronary artery. The computational domain has been determined from CT images of human heart. In this study, blood is assumed to be homogeneous, Newtonian and the blood flow assumed to be pulsatile. In order to more realistic modeling of flow and pressure, Seven–element lumped model has been used in coronary artery outlet, in order words the 0D and 3D models are coupled together. The results indicate that the calculated flow wave is the minimum in systolic phase and maximum in diastolic phase in coronary artery, in contrast with Aorta. On the other hand, by increasing the stenosis percent from 30 to 60 percent, no significant drop of flow has been observed in the state of rest, and it has been validated with experimental results. The results indicate that with increasing stenosis, time average wall shear stress in the stenosis region increases, while it decreases before and after the stenosis, also the investigation of oscillating shear index indicates that in the state of 60% of stenosis and in the main downstream branch, it has the maximum value, that is indicative of the presence of turbulent flow in this region.

In this study, the natural convection heat transfer is numerically examined in a square enclosure filled with a non-Newtonia power-law fluid. Two fixed temperature baffles are mounted on the left wall of the enclosure. The left wall of the enclosure and the baffles installed on it, are at a constant temperature of T_h and the right wall of the enclosure is at a constant temperature of T_c, while its horizontal walls are thermally insulated. The governing equations for the power-law fluid flow are solved with the numerical finite difference method based on the control volume formulation and SIMPLE algorithm. The study investigates the effects of relevant parameters such as the Rayleigh number (〖10〗^3≤Ra≤〖10〗^6), the power-law index (0.8≤n≤1.4), the baffles length (0≤B≤0.5) and the baffles distance from each other (0.1≤D≤0.8) on flow and temperature fields and the rate of heat transfer. The results show that an increase in Rayleigh number, particularly when n

The incompressible Newtonian and non-Newtonian fluid flow in a tube with disk insert is studied numerically using finite volume and boundary fitted coordinate method. The non-Newtonian fluid is time independent purely viscous that is simulated by the power law model. The effects of power law index، thickness، aspect ratio، Prandtl number and the distance between insert tubes on heat transfer، pressure drop and overall enhancement ratio (OER) are investigated for the Reynolds numbers 500، 1000 and 1500. The results show that the effect of power law index on pressure drop and overall enhancement ratio is more than the other parameters.