مجله مکانیک سیالات و آیرودینامیک
سال یکم شماره 1 (پاییز 1391)

Knowledge of fluid flow can play a basic role in optimizing mixing processes. In preparation of sodium perborate, sodium metaborate and hydrogen peroxide, as raw materials, mix and react in the presence of a turbine mixer. In this investigation, the effect of the presence of baffle in a mixing tank equipped with a two impeller turbine agitator was studied. At first, steady state flow in the tank with and without baffles was modeled. The results show that application of baffles causes reduction of mean velocity in the tank. In contrary, radial and axial velocities increase. Secondly, the results were used for unsteady modeling, which showed that addition of baffles in the tank causes increase of mixing quality and reduction of the required mixing time of more than 60%.

The aerodynamics of road vehicles has frequently been studied in simplified geometries to separate the effect of various components on aerodynamic drag and on near wake flow dynamics. In this work, the characteristics of the near wake of a Notch-Back car model were investigated, using hot-wire anemometer. The main objectives of this study are to gain a better understanding of the flow structure in the near wake region. The time-averaged and the fluctuating components of velocity were measured for the car model at various distances behind it. The effect of distance behind the car model to create maximum and minimum peaks of speed and turbulence intensity has been also investigated. Inter-model non-dimensional spacing was varied from 0.1 to 3.0, based on the lead model length. Surprisingly, significant drag increase was found for the rear model for spacing 0.1-1.3.

In this paper, reduced order proper orthogonal decomposition method has been used for simulation of unsteady incompressible flow fields. After projection of the governing equations along POD modes, a low-dimensional dynamical system is achieved. Normally, standard low-dimensional models, due to some reasons, do not predict time variations of flow field accurately. Accuracy of dynamical system has been improved by using a linear calibration term. The presented method is based on combination of POD and an optimization problem, which is solved using least square approach. The obtained reduced order model can predict time variations of flow field with relatively fast computational speed and good accuracy. This method is based on a local minimization technique proposed by these authors. The results have been compared with direct numerical simulation (DNS) data and shows good accuracy and simplicity of the computations.

Boundary layer growth and hence displacement thickness are the key factors in shock position over aerodynamical surfaces at transonic regimes. Since boundary layer growth is a function of free stream Reynolds number and also of the transition location, the free stream Reynolds number and also the other parameters involved in the boundary layer growth and its transition location are determinant in positioning the shock formation and also in aerodynamical forces and moments on a body at transonic regimes. In this paper, the quantitative role of Reynolds number on aerodynamical forces and moments of an AGARD-B model has been investigated. Also, from the results of wind tunnel testing, the blockage of the flow is another effective parameter in the accuracy of the results.

In this work, a numerical study of sheet cavitation has been performed on DTMB4119 marine propellers, using boundary element method (based on potential flow assumption). In propeller design, various parameters of geometry and flow are incorporated. So, a computer program is needed to take all parameters into account and solve the flow. Capability of analyzing the wetted and cavitating flow around propellers in steady, unsteady, uniform, and nonuniform conditions, while decreasing of computational time, with acceptable precision, are the characteristic features of the present work. Moreover, modifying the position of the detachment point and its corresponding potential value have been considered. Numerical results have been validated with experimental data, showing satisfying agreements.

The aim of this work is to find an efficient aerodynamic-based design algorithm for projectile fins and configuration shape optimization. Three-dimensional supersonic flow over a projectile with fins at Much number 5 and one degree angle of attack was studied. The Runge-Kutta method and multi-block technique was used to solve the governing equations. A basic configuration was assumed for the fins. The front and rear straight edges of the fins were replaced with polynomial curved edges and the aerodynamic effects were considered. Using this method, the optimized shape of these edges were achieved. At this step, the geometrical parameters of fins and projectile were changed and their effects on drag and stability moment were investigated. The CFD code was ran for several different geometries and the effect of each parameter was investigated. At the end, the design algorithm of fins was derived and configuration shape optimization of projectile’s body and fins for one example was presented.

Active flow control has great importance in design of flying objects in general and control flaps in particular. Using dielectric barrier discharge as plasma actuators over control flaps can cause a change in position of separation point or can eliminate it. This new flow control device produces a body force that causes generating a micro wall jet. The present study aims to investigate experimentally the effects of the plasma actuator over a NACA0012 airfoil in high angle of attacks (up to 6 degrees above the stall) in order to displace the separation point. Therefore, the effects of the plasma actuator with sine wave unsteady excitation and different duty cycles on airfoil pressure coefficient distribution and lift coefficient were studied. The experiments were performed at  = 3.7 × 10. The plasma generation was performed, using a high voltage AC power supply at voltages up to 14. The results indicate that lift coefficient increases with unsteady plasma actuation at post stall angles of attack up to 6 degree. The improvement of the pressure coefficient distribution in upper side of the airfoil for lower duty cycles about 14% is better than higher duty cycles above 50%.

This paper presents the results of a numerical study on the removal process of fluid particles under the influence of mixed convection in a horizontal channel with an open cavity. The bottom wall of the cavity is heated at a constant temperature (Th), while the top wall is maintained at a relatively low temperature (Tc). Fluid with a uniform velocity (uo) and temperature (Tc) is introduced into the channel. The analysis is carried out for a wide range of values of Grashof numbers (101 ≤Gr ≤105) and Reynolds numbers (10 ≤ Re ≤ 1000). The results show that the removal process of fluid particles increases by the increase in Grashof number, while decreases by the increase in Reynolds number as the well as Cavity’s aspect ratio.