No abstract

No abstract

Abstract. In this study, effect of plasma actuator on a flat plate and manipulation of flow separation on NACA0015 airfoil with plasma actuator at low Reynolds numbers were experimentally investigated. In the first section of the study, plasma actuator which consists of positive and grounded electrode couple and dielectric layer, located on a flat plate was actuated at different frequencies and peak to peak voltages in range of 3-5 kHz and 6-12 kV respectively. The induced air flow velocity on the surface of flat plate was measured by pitot tube at different locations behind the actuator. The influence of dielectric thickness and unsteady actuation with duty cycle was also examined. In the second section, the effect of plasma actuator on NACA0015 airfoil was studied at Reynolds number 15000 and 30000. Four plasma actuators were placed at x/C = 0.1, 0.3, 0.5 and 0.9, and different electrode combinations were activated by sinusoidal signal. Flow visualizations were done when the attack angles were 0°, 5°, 10°, 15° and 20°. The results indicate that up to the 15° attack angle, the separated flow was reattached by plasma actuator at 12kV peak to peak voltage and 4 kHz frequency. However, 12 kV pp voltage was insufficient to reattach the flow at 20° angle of attack. The separated flow could be reattached by increasing the voltage up to 13 kV. Lift coefficient was also increased by the manipulated flow over the airfoil. Results showed that even high attack angles, the actuators can control the flow separation and prevent the airfoil from stall at low Reynolds numbers.

The behavior of a stationary circular cylinder with an attached plate, under conditions where the entire cylinderplate body rotates about the cylinder axis, has been investigated experimentally for Reynolds numbers between 8 × × 10 3 and 6 × × 10 4 . To see the effect of the plate inclination on the pressure distributions and vortex shedding, the cylinder-plate body was rotated from 0 to 180 deg, unlike freely rotatable cases in previous studies. The plate was located at the center plane of the cylinder, upstream of the cylinder, at the beginning. The diameter of the cylinder and the width of the plate were both chosen to be 35 mm. Measurements of shedding frequency and pressures on the surface of the cylinder were obtained. The results indicate that the shedding frequency was nearly constant in the range of 50-120 deg and, by further increasing the angle from 120 to 160 deg, it strikingly increases and then again decreases at angles larger than 160 deg. The plate also causes important changes in pressures on the surface of the cylinder with increasing inclination angle. For different plate angles, five different types of pressure distributions have been observed. Characteristics of the vortex formation region and location of flow attachments, reattachments, and separations were observed by means of the flow visualizations. The drag coefficient of the cylinder has a maximum value at approximately θ = 75 deg, whereas it has a minimum value at θ = 15 deg. The lift coefficient has two maximums, at θ = 15 and 165 deg, depending on the plate position. The values of C L at about θ = 45 and 160 deg are zero as in the case of the cylinder without a plate. Nomenclature C D = drag coefficient 1 2 2π 0 C p · cos α dα C L = lift coefficient − 1 2 2π 0 C p · sin α dα C p = pressure coefficient, (P − P st )/ 1 2 ρU 2 D = diameter of circular cylinder D = projected cross-stream dimension of the cylinder-plate body f = vortex-shedding frequency L = width of the plate P = surface pressure P st = static pressure in the test section Re = Reynolds number based on D, U D/ν Sr = Strouhal number, f D/U Sr = Strouhal number, f D /U U = freestream velocity x, y = streamwise and lateral coordinates α = circumferential angle measured from the stagnation point of the cylinder θ = plate angle ν = kinematic viscosity of fluid ρ = density of air

No abstract

No abstract

No abstract

No abstract