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This paper deals with the effects of duty cycle on improvement of pressure distribution over a NLF0414 airfoil using the plasma actuators. Three Dielectric barrier discharges as the plasma actuators are flush mounted on the airfoil surface in different positions to improve pressure distribution at post-stall angles of attack. The experiments were performed in wind tunnel with pressure tabs measurements at Re_c=7.5×〖10〗^5. The main objective of these experiments is to find the most effective duty cycles for different excitation frequencies and different angles of attack. Results show that the plasma actuators in unsteady excitations are more effective in lower duty cycles on low excitation frequencies but the lower duty cycles lose their effectiveness on higher excitation frequencies.

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Plasma actuator is one of the newest devices in flow control techniques which can delay separation by inducing external momentum to the boundary layer of the flow. The purpose of this paper is to simulate a NLF0414 airfoil both experimentally and numerically in presence of the body force vector induced by a specific plasma actuator. For this reason, the simulation is done both numerically and experimentally for a NLF0414 airfoil with the compressible 25 m/s velocity airflow in two different cases: with no plasma actuator located on the airfoil and with body force produced by a plasma actuator located on the top of the airfoil in order to investigate the effect of plasma on the flow passing over it. The results showed that presence of a plasma actuator on the top surface of the airfoil, close to the separation point, transferred the separation point from x=16 mm to x=41 mm at the angle of attack of 18 degrees. This separation delay caused a 35% increase in the ratio of lift to drag coefficient or the efficiency of the airfoil in the same angle of attack.

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In flows with high Reynolds inside the U-shaped tubes separation phenomenon occurs in the curvature of tubes that causing pressure loss and in conditions associate with heat transfer causes undesirable increase surface temperature in that region. Due to reduced heat transfer rate from surface to fluid temperature increase occurs that in industrial applications in addition to reduce heat transfer causes damage to surface pipes. in the present study, elimination of the separation zone through body force created by plasma actuators and because it reduce the maximum temperature occurred in this region and changes the Peclet number is simulation in this region. For this purpose, the plasma actuators 5kV, 12kV and 19kV with square voltage function inside U-shaped tube in the three streams with Reynolds 3000, 4500 and 6000 have been placed to Influence of actuators on separation control and maximum temperature occurred at this point be investigated. Calculations with using of proposed model of Suzen with time-dependent numerical procedure has been done. And results during time performance of 0 to 50 have been reported. The results shows that maximum surface temperature that occurs in the region of separation in the presence of plasma actuator near this region has a significant reduction that is due to the elimination and change separation region.

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The ability to control the flow, is one of the basic needs of Fluid Mechanics that constantly pursued by researchers. One of the new methods in this area, is using Dielectric barrier discharge (DBD) plasma actuators that by injecting momentum into the boundary layer, causing a delay in the phenomenon separation. The main object in this work was to help to optimize the electrical parameters to obtain stranger vortex and more effective ionic wind created by steady and unsteady plasma actuators on the air through the flat plate. For this reason, simulation is done for a flat plate with the compressible 5 m/s velocity airflow. The time averaged velocity profiles of the ionic wind show that averaged velocity come more and the position of the maximum velocity come near the surface by increasing the excitation voltage and frequency. The power, of the vortices that are shed form the unsteady actuator, increases by increasing duty cycle percentage. Our results on the ionic wind velocity on different position on the flat plate indicate that the maximum averaged velocity occurs in downstream of plasma actuator.