مجله مکانیک سیالات و آیرودینامیک
سال دوم شماره 4 (زمستان 1392)

In this paper, changes of Casson Non-Newtonian fluid velocity profile, for different distribution of porosity, have been investigated. For distribution of porosity, fixed, radial and exponential variations has been considered. For all three states, Brinkman model has been used as momentum equation. Since the Casson fluid is a good model for blood, this analysis can be used in studying about Cholesterol and fat in the blood. For all of the desired states, general movement equation and Casson equation have been analysed for finding the velocity distribution and finally the results of all three states and Newtonian state have been shown and compared.

The present work is focused on the performance analysis of a 1.7 liter engine with turbocharger. The ultimate target is studying the response of the turbocharger to the inlet pulsating flow. Such numerical analysis requires the time variation of pressure and velocity at turbine inlet. In order to achieve such information, one dimensional unsteady viscous compressible flow within a 1.7 liter turbocharged SI engine is modeled. It is also necessary to validate the results of simulation by experimental results. A test setup of the turbocharged engine on dynamometer is prepared and various performance parameters are measured at 12 different engine speeds. The comparison between experimental and simulation results shows a very good agreement. In fact, while the mean values of static pressure and temperature at various stations in both experimental and computational approach are fitted fairly on each other, but the amounts of instantaneous parameters are obviously a little bit different. One of the possible sources of errors is the characteristics maps of the turbocharger supplied by the manufacturer which are usually measured at steady operation of turbochargers. The results obtained in the present report will be used in simulating three dimensional unsteady compressible flow in turbocharger turbine which will be reported very soon.

In this article, an algorithm for designing of a supersonic wind tunnel injection nozzle ejector is presented and based on this algorithm, a new ejector is designed for a supersonic wind tunnel. The injection nozzle consists of a volute, a nozzle, and several vanes. Designed injection nozzle is simulated numerically, and the results are compared with thepresent injection nozzle. The results show the efficiency in the designed version is higher about 2.1%. Besides, the flow uniformity of the new injection nozzle is better and other are occurred in it. Scale-up and mapping the pre designed aerodynamic curves with inverse design method, and use it for other similar cases is one of the innovations of this article.

In this work, a direct design approach for designing a surface shape (inverse design problem) has been developed, in which both the target surface pressure and the unknown nodal coordinates appear explicitly in the formulations. Thefinal discretized form of the governing equations (unified formulation) can be used for both analysis and shape design problems. In this work, shape design problems in the context of steady, in viscid, and compressible flow, based on the three-dimensional Euler equations, were directly solved to achieve a prescribed pressure along solid boundaries. The AUSM+ scheme, in which the in viscid flux is split into convective and pressure components, was used to discretize the flux terms in the Euler equations. Conversion of the AUSM+ formulations into a novel implicit form was performed in this study. The approaches for robustness, especially in the cases where there exist shock waves in the flow, were validated. Two different models for the design of three-dimensional ducts were used and both of them worked properly. Our test cases are applied in convergent-divergent nozzles in wind tunnels and S-shaped diffusers in the airplane inlet engines.

In this study, the turbulent kinetic energy redistribution process is investigated. To this aim, the direct numerical simulation (DNS) of incompressible flow of a Newtonian fluid through a channel at a shear Reynolds number of Reτ = 180 is used to produce a flow data base. Then, these data are statistically analyzed. The turbulent kinetic energy redistribution is studied using the pressure-strain-rate correlation tensor. Pressure and strain-rate fluctuations as well as the correlation coefficient between them are analyzed. An equation for the strain-rate fluctuations is derived whose terms are calculated based on the simulation results. Then, using a semi-analytical solution, the pressure-strain-rate correlation is computed and compared with the DNS results. The results of this research quantitatively show that the pressure strain-rate correlation transfers the kinetic energy that is produced in the stream wise component to the other two components.

Influences of three prevalent mass transfer models, on modeling of cavitation, are investigated numerically. Two models of Singal and Zwart are implemented in an open source code, Open FOAM, while the Kunz model is available for cavitation modeling. Each model is used to flow simulation through a venturi. Volume of gas fraction, in the specified sections of conduit, is compared to experimental data. High precision numerical results are obtained in compare with experimental data using Kunz, Singhal and Zwart models, which they demonstrate less than 5 percent in relative errors. Kunz, zwart and singhal models, results in 2.93%, 3.71%, 4.01% relative errors respectively, in average. Although, there is not a significant advantage between the averaged results of Kunz and Zwart models, Zwart model represents more precious results in initial position of cavitation appearance, where the Singhal model shows the accurate results too.

In this paper, a very fast engineering method is introduced to estimate convection heat flux on axisymmetric and hypersonic projectiles. For calculation of properties flow at the edge of boundary layer (pressure, temperature and velocity), the results of in viscid flow analysis reported in tables (from a Russian reference) was used and for viscous region, Zoby’s convectionheat transfer equations was implemented. Moreover, real gas assumption was used for thermo physical properties of the fluid, The main goal of this research is to develop avery fast computer code for aero thermodynamic calculations of hypersonic cvehicles that may be used as a tool forde signing of heat shields. The results of the present method were compared with those of the other researchers and there is good agreement between them.