مجله مکانیک سیالات و آیرودینامیک
سال سوم شماره 4 (زمستان 1393)

The purpose of this research is to numerically investigate the interaction of pulsatile flow of blood with an axisymmetric artery in various percentages of stenosis. The Carreau non-Newtonian model and the generalized Maxwell rheological model were used to model the blood fluid and the viscoelastic wall of arterial, respectively. The innovation of the present research is modeling of viscoelastic wall for the artery and non-Newtonian fluid for blood to study atherosclerosis. The results were compared with previous reliable data to investigate the validation and accuracy of owr simulation. This showed good agreements. In this study, the effects of stenosis severity on velocity profile, pressure distribution, wall shear stress, and radial displacement have bewere analyzed for viscoelastic artery and they were compared with an elastic artery. A growth in the stenosis severity leads to the increase of the length of vortices, wall shear stress, and velocity gradient after stenosis regions. Also, for severe stenosis in viscoelastic arteies, compared to the elastic arteries, the maximum values of velocity profile and radial displacement of arterial wall increases 2 percent and decreases 22 percent, respectively. Development of atherosclerosis increases the elastic modulus and causes 64 percent reduction in radial displacement of the artery walls. Also, with growth of 5 times in the elastic modulus, a 11 percent increase in velocity magnitude and a 12 percent growth in pressure value of the blood flow were observed.

Natural convective heat transfer of nano-fluid in porous media is present in many advanced engineering applications. In this work, this problem has been computationally simulated, using LBM. The configuration used includes a cold exterior region and hot interior cylinders with one-, two-, or three-cylinder arrangements. However, the effective area for heat transfer has been kept the same for all three cases. A D2Q9 grid has been used. for To consider the porous media, the related source term has been considered in the equation of relation density distribution function (the Brinkman-Forchheimer model has been used). Our results have been validated using previous available valid data which shows relatively close agreements. The effect of Rayleigh and Darcy numbers, porosity, and arrangements of the cylinder(s) on the Nusselt number of the cold region wall and also the heat transfer performance of the configuration have been investigated in this work. Our results closely simulate the nano-fluid behavior inside the porous media. The results show that as the Rayleigh and Darcy numbers and porosity increase, natural convective heat transfer is enhanced. In addition, as the number of cylinders increases, such heat transfer is enhanced considerably. Finally, as expected, as the nano-particle’s void fraction increases, convective heat transfer is increased.

Nowadays, CAD/CAM simulation is considered as a strong tool to estimate performance of various systems and to reduce costs and testing time. In this study, we used GT-Power Software to model the performance of an SI engine. The results indicate that the engine power drops significantly as altitude increases. To compensate power loss, the engine is equiped with a turbocharger system. The proper turbocharger was selected with regard to the surge and choke limits of its compressor, as well as its compatibility with the engine (at mass flow rate point of view). To avoid engine knock, we used a special wastegate mechanism. Also, to reduce the temprature of the flow after compressor, we defined a proper type of intrcooler system. we used the experimental results derived in our engine lab. The results show that by using turbocharger and intercooler, the engine brake power improves. In addition, the specific fuel consumption decreases and the volumetric efficiency increases. Also, NOX emission reduction and safer cyclic performance of compressor are the effects of intercooling.

Aerodynamic simulation of APDS projectile with and without sabot has been conducted here. Due to less weight of APDS projectile in comparison with the projectile, with the same caliber, APDS projectile has higher muzzle velocity, longer range, high penetration capability, and higher impact velocity. Simulation of flow around the sabot walls has been carried out in two opening degrees of zero and 75 at supersonic regime, using the 3D Spalart-Allmaras turbulence model. Problem verification has been tested, using the wind tunnel drag coefficient experimental data at two opening degrees of zero and 75 and close agreements have been obtained. The drag coefficient has been used in the ballistic coefficient calculations, wherein 24 percent improvement has been attained.

In this study, aerodynamic characteristics of a circular cylinder in an axial flow have been investigated numerically and experimentally. The model has been considered as a cylinder with truncated nose and fineness ratio of 3 (length to diameter ratio of 3). The investigation involves a series of wind tunnel measurements, flow visualization, and numerical simulation. We used different Mach numbers, ranging from 0.3 to 2.4, to cover subsonic, transonic, and supersonic flows. The flow visualization through Schlieren imaging was en performed at supersonic flow to study separation bubble and shock wave formation on cylindrical body. Axial force coefficient results show that this unconventional shaped cylindrical body with truncated nose and low fineness ratio has significant drag value, which is an order of magnitude larger than most high fineness ratio and pointed nose cylindrical bodies. The results show that by increasing Mach number, the shock stand-off distance is decreased and the strength of the shock is increased. The comparison between numerical and wind tunnel test results shows good agreements with reasonable accuracy to estimate aerodynamic force coefficients and flow structure.

Shock formation due to flow compressibility and its interaction with boundary layer has inappropriate effects, such as drag increase and flow separation. Many methods have been proposed for reduction of these effects, such as vortex generator, suction, and blowing. This paper numerically studies the problem of flow control for NACA0012 airfoil with porous media at transonic flow. Porous media, which combines blowing and suctionm reduces these inappropriate effects. The effects of porous media depth, length, porosity, cell diameter, and angle of attack are investigated in this study. The numerical method is finite volume and the equations are Navier-Stokes. The flow is assumed to be turbulent and stationary. The Results show that the normal shock intensity is weak and consequently the drag coefficient decreases 20 percent. The weakened shock is moved upstream and top of the porous surface region and the shock Mach number is decreased 10 percent. This passive method also postpones the separation point from 58 to 72 percent of the airfoil chord. The efficiency of this method depends on various factors, like geometric parameters.