جستجوی مقالات مرتبط با کلیدواژه « ضریب پسا » در نشریات گروه « برق »

Designers try to reduce missiles’ drag coefficients, but many of the geometrical changes that reduce the drag coefficient can increase the radar cross section of the missile. So, authors decided to solve this problem by missile optimization. In this study, missile Ogive nose is optimized using multi-objective genetic algorithm while the length of missile is kept constant. Objective functions are drag coefficient and radar cross section (RCS). Ogive nose was tested in mach number of 2.01 and radar systems were designed to operate at high frequencies between 4-6 GHz. The drag coefficient was calculated by CFD code and was compared with experimental results. Then, radar cross section was calculated with the commercial HFSS program. Finally, objective functions were optimized using non-dominate sorting genetic algorithm (NSGA-II) and the objectives were both minimized to establish the Pareto front. Pareto front shows the best possible design points for the objective functions. Compared with the initial model, the optimum model achieves a decrease of 47% and 14% in the drag coefficient and the radar cross section respectively.

One approach to improve the aerodynamic performance of airfoils and hydrofoils is inject a small amount of energy to the system (such as fluid injection or suction on the surface), to change the lift and drag. In fact, surface suction and blowing of the fluid can improve the pressure distribution and velocity gradient on the airfoil/hydrofoil surfaces and modify the flow separation point. Therefore, in this study the hydrodynamic behavior of turbulent flows over an airfoil exposed to the injection and suction of fluid in a part of its upper surface is discussed. Firstly, the behavior of the airfoil under one position of the injection or suction and then under two positions of injection or suction are investigated. In this simulation, the FLUENT software is used. The aim of this study is to investigate the effect of the power, the number, the position and the angle of blowing or suction on the hydrodynamic performance of the airfoil. The most important results are the reduction of 10 to 50 percent of the drag and the increase of 5 to 10 percent of the lift (for the blowing) and the reduction of 5 to 30 percent of the drag and the increase of 5 to 10 percent of the lift (for the suction) by considering two positions of injection in comparison to one position.

In recent years, environmental concerns are the greatest challenge in vehicle design. Electric vehicles seem to be a suitable solution to this problem. Therefore, numerous measures have been taken to increase the efficiency, reduce losses, and improve the performance of these vehicles. Aerodynamic characteristics improvement is a key issue that should be considered in vehicle design. In this paper, the effects of improving the aerodynamic characteristics on the electric vehicles are analyzed. For this purpose, installing movable rear spoiler along with a controller and covering the rear wheels have been proposed. In order to evaluate the proposed solutions, their effects on an electric vehicle prototype that has been constructed and developed by the authors have been modeled in MATLAB SIMULINK environment. The flow around the electric vehicle has been studied in ANSYS in order to calculate the drag and lift coefficients. The flow has been numerically solved using the Computational Fluid Dynamics (CFD). The standard k-ε turbulence model has been utilized in this study. The results show that improvement of aerodynamic characteristics in electric vehicles not only increases the stability of the vehicle, but also has a significant impact on the energy storage system, mileage, and the electric motor efficiency.