Journal of Aerospace Mechanics
Year:2010 | Volume:6 | Issue:1 (19) (FLUID MECHANICS AND AERODYNAMICS)|Papers Count:8

In this research, the three-dimensional flow in a centrifugal turbocharger compressor has been numerically simulated. The flow through impeller and diffuser is modeled to obtain the compressor performance map. Also, the side-space between the impellers and the casing is simulated, in order to model the entire compressor. For the moving zones, multi-rotating reference frame approach was used. Performance maps obtained through both numerical and experimental data (measured by the authors) are relatively close indicating the high ability of numerical approach used to simulate complicated flows, such as flow in turbo machineries. The secondary flow and the clearance loss caused by the impeller were well predicted by the present numerical simulation. Also, the shroud configuration and the tongue location were shown to have high impact on the compressor pressure rise and on lits efficiency.

The purpose of this investigation is consideration of aerothermodynamic phenomena over blunt and slender pointed bodies in hypersonic flows. Such results may be obtained by numerically solving the full Navier-Stokes equations or one of their various subsets, such as PNS equations. However, due to the excessive computer storage and CPU requirements, most people use their simple forms. In this work, a computer code was developed that uses an implicit finite difference method to solve non-similar, full compressible boundary layer equations for laminar, transitional, and turbulent flows over blunt and slender pointed bodies in hypersonic flows. Different test cases were studied and the related results were compared to benchmark CFD and experimental data showing relatively close agreements.

In the classic continous model, assuming velocity field, one can completely define the problem. However, this is not suitable for the analysis of complex flows. On the other hand, according to the non-Newtonian behavior of blood, it seems that the use of theory of micro-polar fluids, based on the Cosserat continous model for the investigation of blood pulsatile fluid, is logical. The goal of this paper is to derive the analytical velocity field for comparison with suitable experimental velocity field in the future. In this paper, a comparison has been carried out between the results of the two Cosserat and classical models according to spinning condition on the wall. Using Laplace and Hankel transformations, we could analytically solve the pulsitive flow of Cosserat fluid.

In this paper, the thermo-hydro dynamical analysis of incompressible flow in conjunction with cell-centered finite volume-lattice Boltzmann method (FV-LBM) was developed. To demonstrate the temperature field, the double distributions function (DDF) was used. A novel approach was applied in cell flux calculation by definition of biasing factors based on pressure and temperature. This treatment enlarges the domain stability and leads to faster convergence. A consistent open and solid boundary treatment of flow was also addressed. The unknown energy distribution at the boundary cells were decomposed into its equilibrium and non-equilibrium parts. Then, the nonequilibrium part was approximated with extrapolation of the non-equilibrium part of the populations at the neighboring nodes. Two test cases namely, thermo-hydrodynamic in a backward-facing step and around a circular cylinder inserted within the backward-facing step were carried out. The results were compared with the available solutions in the technical literature showing reasonable agreements.

In this paper, an analytical solution for the second order fluid flow in a curved pipe is presented. Perturbation method is used for solving the governing equations and unlike the previous researches, the second order perturbation terms were considered. Here, an analytical relation for the flow rate was presented and axial velocity, secondary flows, and components of stress field were calculated accurately. Also, based on the solution of second order fluid flow presented in current work and upper convected Maxwell fluid flow obtained in previous studies, the effect of retardation and relaxation times of viscoelastic fluids on flow in curved pipes were investigated. In this article, it was shown that increasing the retardation and relaxation times cause the flow rate enhancement and reduction, respectively, which is one of the main innovations of current study.

The interaction between the wakes of two or more bodies is important in many industrial applications, e. g., aerospace system and cooling fans. In this paper, the velocity field and the turbulence of the wake generated behind an airfoil in the presence of a circular cylinder were studied experimentally, using hot-wire anemometry. The basic parameters of this study included horizontal and vertical distance between the airfoil and the cylinder and the flow Reynolds number. The modeling was carried out according to the ratio of cylinder diameter to airfoil chord (d/c) as well as the relative location of the airfoil and the cylinder. The Reynolds number based on cylinder diameter was 14300 (wind tunnel test section is 305x305mm2). Due to the frequency of vortices, the sampling rate of the experiments was set to 2kHz. The results of this research offered data such as turbulence intensities, Reynolds stresses, and vortex frequency in the near wake region. Turbulence intensity was investigated in the vicinity of near wake behind the cylinder. Some of the vortices frequency were compared with the existing results showing relatively good agreements.

This paper presents the results of a series of experimental and numerical studies concerning wake velocity profile, turbulent fluctuations, and the drag force associated with flow around a triangular prism. For this reason, a triangular cylinder with apex of 60o with various Reynolds numbers was tested. A 3-D hot wire probe was used to experimentally determine the velocity field around the cylinders in a low subsonic wind tunnel. Using the measured flow velocities behind and in front of the cylinder, drag coefficients were also calculated. The experimental results are in good agreements with the ones related to previous works.