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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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This paper deals with experimental measurements of the instantaneous ionic wind velocity induced by Dielectric barrier discharge (DBD) plasma actuator in quiescent air at atmospheric pressure. A parametric study has been performed in order to increase the velocity of the ionic wind induced by the DBD actuators. The electrical and mechanical characteristics of the plasma actuator have been studied under different conditions. The main objective of this work was to help to optimize the geometrical and electrical parameters to obtain more effective ionic wind for flow control. The time averaged velocity profiles of the ionic wind show that the position of the maximum velocity come near the surface by increasing the excitation frequency. Our results indicate that the DBD plasma actuators generate vortices at the same frequency of the excitation frequency of the applied high voltage. The power, of the vortices that are shed from the actuators, increases by increasing duty cycle percentage. Unlike other similar works in this field, this study has examined the behavior of unsteady plasma actuator.

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In this research experimental results of 60 degree delta wing airplane that conducted in National Low Speed Wind Tunnel is presented. The wind tunnel is closed type has an opened test section that its dimensions are 2.8 m × 2.2 m. Tests Reynolds number is beyond 1.5 million that achievement of this Reynolds number at low speed is unique in the country. Ground effect is measured using a fixed plane that its height is variable. Tests are conducted at the different height and aerodynamics forces and moments are measured using a sting type six component strain gaged balance. The tests results showed that the maximum lift coefficients increased from 1.29 to 1.38 due to presence of the ground plane. The lift coefficient due to ground plane in all range of angle of attack is increased and induced drag coefficient is decreased and consequently, the overall aerodynamics efficiency (lift to drag ratio) is increased from 8 to 14.5. When the distance between model and ground plane is less than half of the wing span, lift curve slope is increased in high rate from 2.66 per radian to 3.11 per radian. Decreasing this distance is caused the aerodynamic center is shifted backward and consequently longitudinal static stability is increased. Consequently presence of ground plane is caused increasing of airplane static stability.