FLUID MECHANICS AND AERODYNAMICS JOURNAL
Year:2019 | Volume:8 | Issue:1 (23)|Papers Count:6

In the present work, wind shear flow (atmospheric boundary layer) effects on aerodynamic performance of the NREL 5MW baseline wind turbine were investigated. In this regard, the steady three-dimensional actuator disk method, based on computational fluid dynamics with low computational cost, was developed, utilizing user-defined function (UDF) in a finite volume-based commercial software package. The rotor was not modeled directly, such that its momentum effect was added to the Navier-Stokes equations as a body force (source term). The developed solver was adopted to compare the flow field behavior around the rotor under uniform and wind shear inflow conditions. Different cases for the rotor azimuth angle were considered to evaluate the radial distribution of rotor power and thrust. Numerical results show that wind shear inflow leads to skew rotor wake, as well as asymmetrical pressure, vorticity, and velocity fields. Moreover, rotor experiences cyclical loading during each rotation. Note, for the selected wind shear profile of this work, the maximum difference in thrust on the rotor plane is about 125KN for each period of rotation.

In this study, the usual shape of a specific mono-hull changes into tunneled one keeping the geometrical parameters, including deadrise angle, keel line, beam width, and the hull length, constant. In this research, the specific shape of a speed monohull changed into a tunneled, keeping the geometric parameters, including the deadrise angle, keel line, hull width and length constant. The analysis carried out considering full load (10kg) and without load (3kg) conditions and optimization of the tunnel dimensions was performed in the maximum operational weight (10kg) and velocity (10m/s). Various geometrical parameters are effective on drag reduction of different sections of the tunnel, when designing and manufacturing the hull. In order to reduce drag, various geometrical parameters in different parts of the tunnel are effective in design and optimization. In this study, it has been attempted to investigate the effects of three parameters, namely: tunnel aperture, tunnel height, and blade simultaneously, in order to achieve an optimum shape of the tunnel. For this purpose, numerical simulation of the problem was carried out by means of finite volume method, considering moving mesh. For turbulence modeling, kε model and for simulating the free surface, volume of fluid (VOF) method were employed. The design of test and optimization were conducted, using Taguchi method. The results show that the tunnel aperture is the most effective parameter in increasing operational speed. Furthermore, one can reduce the drag by about twenty percent in the operational weight and speed through optimizing the tunnel.

In this paper, water entry problem of three-dimensional projectiles with various geometrical shapes and different drop heights and holes distribution was numerically simulated by coupled Eulerian-Lagrangian (CEL) method and the effect of mentioned parameters on deepwater velocity and pinch-off time and depth was investigated by the commercial software Abaqus 6. 14-2. The numerical results were verified by comparison and proper adaptation with available theoretical and experimental results, such as the movement trajectory of a spherical projectile in water depth, shape of formed air cavity, and pinch-off time and depth, which revealed the accuracy and capability of the numerical algorithm used. The results revealed that pinch-off depth is influenced by projectile geometrical shapes and significantly increases along with increased drop height from free water surface, while the pinch-off time is a very weak function of mentioned parameters. Also, the drag force of water has the highest and lowest effect on flat and pointy-nose projectiles, respectively. Hence, the cubical projectile with the highest velocity depreciation impact on the model bed with a velocity of 1. 57m/sec and pinch-off depth occurs at a depth of 63cm, while the conical projectile with the lowest velocity depreciation has an impact velocity of 3. 88m/sec and pinch-off depth occurs at a depth of 98cm.

The first purpose of this paper was to obtain non-linear equations for describing pressure waves in a liquid with gas bubbles. For this purpose, non-linear equations of fourth order and some of their special cases for describing pressure waves in a mixture of fluid and gas were considered. Then, considering the influence of heat transfer and viscosity in fluid, a differential relation between pressure and perturbation radius of gas bubbles is obtained. It is shown that the Burgers, the KdV and KdV-Burger’ equations are special cases for describing pressure waves. Also, we introduced a G G -expansion method, which can obtain exact solutions of non-linear differential equations without requiring the boundary and initial conditions. In this method, by choosing special constants in the obtained solutions, more solutions of these equations can be obtained. These features exhibit the superiority of the introduced approach. compared to the other methods. Furthermore, exact solutions of these equations are obtained using G G -expansion method, which has many applications in science and engineering.

Axisymmetric bodies, like submarines, at high angles of attack have been characterized by three-dimensional boundary layer separation and large vortical structures, which have an important effect on forces and moments. This vortical flow affects acoustics, drag, and maneuverability. A suitable way to reduce the effect of this separated and vortical flow is to use vortex generators, which have different arrangements, such as counterrotating and co-rotating. The present study aimed to investigate flow field around a standard model employing vortex generators with different arrangements, using a five-hole probe at 0° ≤ α ≤ 20° . Application of five hole probe method can help to precisely study the structure of vortical flow field. The results show that counter-rotating vortex generators do indeed significantly reduce the strength of vortex, size of cross-flow vortices, and drag force.

In the present study, turbulent flow in submerged inlets was studied, using numerical simulation. In the calculations, three different geometries, namely NACA standard inlet and two geometries with proposed structures were studied and the effects of boundary layer thickness (0. 31, 0. 8 and 0. 56) and 0. 2< dimensionless velocity < 1. 6 on their performance were investigated. k   model was applied to simulate three-dimensional, incompressible, and turbulent flow. At first, NACA standard inlet was validated, using reliable experimental data. Results show that increasing boundary layer thickness has a negative effect on RAM pressure efficiency in all geometries, while velocity increase initially increases the efficiency and then decreases it. In addition, the efficiency of new geometries is close to one for NACA standard inlet. Moreover, the novel geometries are of lower drag force in high velocity ratios and are better NACA standard case.