فهرست مطالب mahmood mani

The noise of wind turbines is mainly of aerodynamic origin and is caused by the impact of the flow on the turbine blade. Therefore, improving the behaviour of the flow around the turbine and reducing aeronoise can result in reducing its annoying noise. In the first step of this research, a suitable serration is selected according to the physics of the flow, and then it is installed on the leading edge of the blade in such a way that it does not cause the power loss of the turbine. All the studies have been done experimentally in the wind tunnel and with the help of power, pressure and air velocity measurements in the wake and in the different free stream velocities. The results showed that the pressure fluctuations in the model equipped with a serrated blade have decreased by 4-9% on average in different areas compared to the simple Savonius. On the other hand, the results of the frequency analysis of the anemometer sensors also showed that in the dominant frequencies, the serration caused the range of phenomena to decrease. These results were obtained in such a way that the power measurement showed that the maximum power value of the turbine equipped with serrated blade experienced an increase of nearly 19%. On the other hand, the velocity profile in the wake also shows a greater deficit in the flow around the modified Savonius, which confirms the decrease in the output momentum from the turbine and consequently the increase in power.

Flow control to reduce drag and increase drag and finally increase the ratio of drag to drag (L/D) has always been the focus of aerodynamic scientists. There are many methods to reduce induced drag. The use of DBD plasma operators is one of the newest methods in reducing induced drag. In this research, in order to investigate the performance of DBD plasma actuators, six configurations of plasma actuators have been used as virtual winglets. Experiments have been performed on the wing with the NACA0012 airfoil. These experiments have been carried out in two Reynolds numbers 150,000 and 300,000 and in two voltages, 6 kV and 10 kV and different angles of attack. The results of this research show that the use of this type of plasma actuator at the tip of the wing as a virtual winglet can increase the lift to drag ratio by about 25% in some cases and the use of two small circular and large linear configurations. respectively, they have the best performance compared to other models for use as a virtual winglet.

In the last decade, the use of plasma actuators for the application of flow control has been very interested. One of plasma actuators types is the Dielectric Barrier discharge (DBD) plasma actuator. Its properties include simple structure, fast response time, low power consumption and lack of moving parts. In this study, the changes of pressure distribution before and after plasma formation at different frequencies and voltages were investigated just above surface at the bottom of the flat plate model and the location of the last plasma actuator. Also the effect of voltage and frequency changes on the pressure distribution has been surveyed. The results of the experimental tests indicate that the plasma produces the ionic jet just above surface, in fact, the plasma actuators produce momentum flow in the boundary layer and produce ionic wind. By increasing the voltage and frequency - more than the breakdown voltage - the momentum flow is created in the direction of the plasma actuator. As the voltage increases and the plasma becomes visible and vortexes are formed on the flat plate.

This study focuses on using rotor blade turbine winglets for the purpose of controlling the wingtip vortex in airplanes. The aim of the study is to investigate the effective geometric properties of the rotor blades that are used as winglets, as well as experimental evaluation of their effects on drag, lift coefficient and the aerodynamic efficiency ratio of the airplane. Seven different types of rotor blades were chosen in regard of their span length, number of blades, and the shape of the blades and experimented in a wind tunnel. The drag and lift force were directly measured via a 3-axis external balance. The position and place of installment of the rotor blades were selected through the studies mentioned in the literature and their geometric properties were further investigated. A finite wing with a NACA641412 cross-sectional airfoil, two similar rotor blades with different span length, two similar rotor blades with different blade count, and three rotor blades with different aerodynamic shapes in terms of installation and twist angle were used as models in this study. All the experiments were conducted at a Reynolds Number of 100,000 and angles of attack ranging from negative 4 to positive 20. The results showed the existence of turbine winglets has increased the lift coefficient and results in a reduction in the drag coefficient. Rotor blades with larger span lengths have increased the aerodynamic efficiency, although they have increased the drag coefficient as well. The number of the blades has had different effect in different angles of attack. The results indicate that rotor blades with acceptable aerodynamic properties can increase the value of aerodynamic efficiency almost twice its base value and delay the wing stall up to the  attack angles above 20 degrees.

Spar ignition in turbulent methane-air jet is studied by a compressible 3D Large Eddy Simulation in OpenFOAM code. The thicened flame model with the one-step chemical mechanism is used for methane combustion. The spar is modeled by artificial enthalpy source in energy equation at the spar location. The validation of the calculations is performed using the experimental results of the turbulent jet of airflow and non reacting mixing of methane jet. The ignition phenomenon and flame propagation are investigated in details for different conditions of initial jet temperature. The results show that the flame propagation speed, the flame lift-off and the flame distance to the axis change with changing the initial temperature.

This paper reports on a numerical and experimental investigation of a variable-sweep morphing wing for an unmanned aerial vehicle (UAV) whereby the area and the aspect ratio of the wing can change while its overall configuration is kept nearly unchanged. The numerical results were obtained using computational fluid dynamics (CDF) and the experimental data from a low-speed wind tunnel test at the speeds of 50, 60, and 70 m/s. The extent of change in the sweep angle of the morphing wing relative to the base wing is 12 degrees (i.e. 36%). The results of this study show that lift coefficient, lift curve slope, drag coefficient and the aerodynamic efficiency of the model wing decrease as the sweep angle increases. According to experimental results, the maximum reduction in the drag coefficient of the morphing wing is 6.1% as the sweep angle increases from 33 to 45 deg. Also, the maximum changes in the aerodynamic efficiency of the model with sweep angle changing from 33 to 45 degrees occur at 6 degree angle of attack, which is equal to 11.6%. With changing the wing sweep, the maximum change of flight range and endurance were found to be 8.77 and 7.15%, respectively.

In this research, experiment and computational fluid dynamics (CFD) are used to assess the performance of UAV with variable-span and sweep morphing wing under low speed conditions. Both wing area and aspect ratio are changed due to variations in span and sweep, whereas structure of the variable-span and sweep morphing wing remains constant. In this study, the numerical results of Fluent software and experimental data are presented. Results are achieved under a low wind speed (50, 60 and 70 m/s). In this case, full extension represents a 30% (10 cm) increase in wing span and 36% (12 deg.) in sweep angle relative to the original wing, with no extension. The results of this study show that the morphing wing is capable to improved aerodynamic efficiency, increased both range and endurance, reduced induced drag and in general reduced thrust required. According to experimental and numerical results, the use of morphing wing can increase the range by 13.6% and 13.5%, also, endurance of the vehicle by approximately 8.855 and 8.17%, respectively. The results of this study show that the maximum value of lift-to-drag ratio occurred at 6 degrees angle of attack and a speed of 70m/s. These results demonstrate that the use of morphing wing improve the lift-to-drag ratio by 10% compared to original wing. Finally, the numerical simulations are compared and show good agreement with the experimental results. This research also showed how morphing concept can be used as an alternative method for roll control.