مجله مکانیک سیالات و آیرودینامیک
سال چهارم شماره 2 (پاییز و زمستان 1394)

In this paper, the fluid-structure interaction phenomenon and the research history are described. Then due to the complex and specific working conditions of a turbine blade, we have investigated the phenomenon on this subject. The fluid-structure interaction on a turbine blade model has been simulated by using structural and fluid flow section of ANSYS software. A model of turbine blade with airfoil cross section made of aluminum has been analyzed in three different inlet speed of the fluid. For analysis results the amount of turbine blade tip deviation and its impact on the fluid flow pressure exerted on the turbine blade has been considered. The results show that by increasing the speed of inlet flow, the amount of blade tip deviation increases and also its impact increases on fluid pressure exerted on the rotor. The results also show that the transverse displacement of the blade is linear across of its axis.

In this paper, analysis of fluid flow and heat transfer over the bank of tubes is considered. k-Ω SST model is applied for simulation of turbulent flow. In this paper, the improvement of efficiency of a bundle of circular tubes by changing the shape of the cross section of one row of the pipes to the elliptical cross section as an innovative plan is considered. As know, friction factor in turbulent flow is very important on efficiency of bank of tubes. Therefore, replacement of elliptic cross section shape in a special row in the bank of circular tubes is considered. Obtained results showed change of tubes in fifth row of the bank of circular tubes with elliptic cross section has been caused 24% increase of efficiency in bank of circular tubes.

The flow characteristics around an elliptic cylinder with an axis ratio of AR=2 located near a flat plate were investigated experimentally. The elliptic cylinder was located on the inside and outside a turbulent boundary layer region whose thickness (δ) is 0.38B. The Reynolds numbers based on the height of the cylinder cross-section were 15000 and 30000. Measurements of mean velocity and turbulence intensities have been made using the hot-wire anemometry when the wake of elliptic cylinder interact with the boundary layer on a flat plate. In the near-wake region, streamwise mean velocity profiles and turbulence intensities were strongly dependent on gap ratio (G/B) and Reynolds number (Re). It is found that, wake and boundary layer interaction except in G/B=0.1, at Reynolds number of 30000 is faster than the 15000. The wake-boundary layer interaction at fluctuating velocity quantities begins earlier than the mean velocity. As the gap ratio increases, the drag coefficient of the cylinder itself decreases, which the decrease value of the drag coefficient at Reynolds number of 30000 is more than the 15000. The results show that the Strouhal number by increasing the gap ratio increases and nearly independent of δ/B. The wake region behind the elliptic cylinder is relatively small and the velocity profiles tend to approach rapidly to those of a flat plate boundary layer.

The most accurate method for calculating the aeroheating is numerical solution method. Using finite volume method to solve the Navier-Stokes equations in time is very time consuming. So by using the finite difference algorithm, transfer equations to curvature coordinate by the mapping function, and combination of the viscous shock layer and similarity of boundary layer, the CTCA Code was developed. Determine the species mass concentration at the wall boundary due to chemical reactions of surface ablation and air dissociation/ionization, is one of the main inputs to solve the flow field around the hypersonic noses. Species mass concentration at the wall boundary due to chemical reactions is dependent on the catalytic wall type or time duration of flow stop at the specified point of wall. For fully catalytic walls, the time duration of flow stop is greater than the time required to equivalence chemical reactions and the wall boundary conditions are determined by using the chemical equilibrium assumption. Also in the non-catalytic walls, the time duration of flow stop is less than the time required to equivalence chemical reactions and they are determined by using the chemical frozen assumption. The severity of wall catalyst is dependent on the recombination average rate of species and this parameter is one of the inputs to solve the problem. Therefore in this study, the wall catalytic effects on the aeroheating of ablative noses were investigated by the space marching method. The result of current research and other similar researches showed that, the fully catalytic at stagnation points and the non-catalytic at body are reasonable assumptions.

A two dimensional finite difference lattice Boltzmann method (FDLBM) for computing single phase flow problems is developed here. Temporal term is discretized with low dissipation-low dispersion. Discretization of convective term is implemented with third order upwind method. It will be explained governing equations and numerical method. Methodology of imposing boundary conditions in FDLBM is described. Then for evaluation, two basic problems will be solved: Taylor's vortices and unsteady Couette flow. The purpose of this paper is the presentation of a robust method to solve unsteady and steady problems.

In this work, the feasibility study for design of a laboratory sample RDE which has an annular geometry with diameter of 76 mm and length of 101 mm has been performed. Detonation engines are expected to be used as propulsion system in aerospace applications in the future. Several types of detonation engines are currently under examination, including the rotating detonation engine (RDE). First, numerical studies are validated comparing the FLUENT results with the experimental ones. Then, the geometry and equivalence ratio of injection mixture are investigated parametrically. Considering the negligible variations of thermodynamics parameters in the radial direction of flow field to reduce the computational costs, also a 2D model is used for numerical simulations. Results show for the case with the equivalence ratio of 1.2, detonation speed, pressure, and temperature behind detonation front is more than the equivalence ratio of 0.8. Also, maximum detonation speed and pressure behind detonation take place in stoichiometric conditions. The parametric study of the chamber length effects was also conducted using a length 0.5 and 2 times of the main chamber. Because the chamber outflow is subsonic at some regions, chamber length change has a significant effect on the engine performance and flow field. The results point out that increasing the chamber length in low injection pressure and high injection pressure leads to increasing and decreasing the height of detonation front, respectively.