فهرست مطالب e. shirani

Murray’s law, as the best-known optimal relationship between bifurcation calibers, is obtained based on the assumption of steady-state Poiseuille blood flow and is mostly accurate in small vessels. In middle sized and large vessels such as the aorta and coronary arteries, the pulsatile nature of the flow is dominant and deviations from Murray law have been observed. In the present study, a general scaling law is proposed, which describes the optimum relationship between the characteristics of bifurcations and pulsatile flow. This scaling law takes into account the deviations from Murray law in large vessels, and proposes optimal flow (i.e. less flow resistance) for the full range of the vascular system, from the small vessels to large ones such aorta. As a general scaling law, it covers both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is that bifurcation characteristics solely depend on the Womersley number of parent vessels. The diameter ratios suggested by this scaling law are in acceptable agreement with available clinical morphometric data such as those reported for coronary arteries and aortoiliac bifurcations. A numerical simulation of pulsatile flow for several Womersley numbers in bifurcation models according to the proposed scaling law and Murray law has been performed, which suggests that the general scaling law provides less flow resistance and more efficiency than Murray law in pulsatile flow.

The velocity of the fluid in every location of the water jacket has a direct relation with the rate of heat transfer. Approximately one-third of fuel heat release in an IC engine is lost to the environment by coolant flow. So, it is necessary to determine the velocity of coolant according to the rate of heat transfer. The water jacket of an engine has complex and non-transparent geometry and it is impossible to measure velocity in each location. In this paper, the velocity of coolant is measured in a transparent water-jacket of the EF7 engine with the PIV method. A volumetric flow rate of coolant is determined according to engine speed that two engine speeds considered in this research. In the PIV method with the dispersion of special submerged particles in coolant on a transparent water jacket and shining of the laser beam to particles, it is possible to track them. Then, with image processing, velocity vectors are carried out with the toolbox of the Matlab program. Extraction of results of the can is used for the study of fluid behavior. Besides experimental work, simulation with Fluent software was done for comparison between results.

In this study the hemodynamic analysis of complete coronary bypass graft with elastic walls and different percentages of stenosis are investigated numerically. Blood flow is considered Newtonian and unsteady. The objective of this study is to deal with the influence of the wall elasticity, flow pulsatility and stenosis percentage on the flow configuration, Wall Shear Stress (WSS) and rotational flows. By comparing the rigid and elastic wall results of WSS, it is concluded that WSS obtains lower values in toe, heel and bed of the host vessel under the bifurcation in the elastic mode, which is closer to reality. Also it is concluded that with increasing the stenosis percentage, the possibility of occurring rotational flow will increase. The maximum and minimum values of WSS are observed in the stenosis of 70%. From the pulsatility of flow, it is observed that unsteady flow shows more accurate results also velocity and WSS have lower values compared with the steady state results.

Improving the aerodynamic performance of the transonic fan in a turbofan engine can be beneficial for both the fuel consumption and maneuverability of an airplane. Deep insight into the supersonic aerodynamics is needed for the simultaneous improvement of all operating parameters of a transonic rotor, including the pressure ratio, efficiency, and surge margin. A design method was developed for an axial transonic rotor by using a combination of radial equilibrium theory, the free vortex method, and a distributed span-wise diffusion factor. The loading distribution obtained by this method was the highest in the hub section and gradually decreased in the tip section. To evaluate the method, a transonic rotor was designed using the geometric parameters and operating conditions of NASA rotor 67. A code was developed to determine a geometry for the new rotor and to modify it. The code was coupled with a RANS flow solver for 3D modification of the new designed rotor. Only standard multi- and double-circular arc airfoils were applied in different radial sections of the new rotor with no blade profile optimization. The results of the RANS equations solution for the new designed rotor showed 1.5% higher efficiency, 3% higher pressure ratio, and more than 1.5 times larger operating range in comparison to NASA rotor 67. The new designed method seems to be an efficient approach that not only improved the efficiency and pressure ratio but also increased the operating range of an axial transonic rotor.