Mechanisms for Conical Forebody Flow Control Using Plasma Actuators

Abstract

Duty cycle modulation of the alternating blowing from two opposite facing plasma actuators on the leeward surface near the apex of a cone of semi-apex angle 10 ◦ to control the mean lateral force and moment and the flow control mechanisms are presented. The pressure distributions over the cone forebody are measured using steady and unsteady pressure-tappings. The flowfields are visualized by a two-dimensional particle image velocimetry. The experiments were perfomed in a 3.0 m × 1.6 m open-circuit wind tunnel at 45 ◦ angle of attack and Reynolds number of 5 × 10 4 based on the cone base diameter. The opposite bi-stable vortex patterns appear when the port or starboard actuator is activated while the other is kept off during the test. The phase-locked (locked to the plasma duty cycle) averaged flow induced by the duty-cycled plasma actuation is periodic and varies smoothly between two opposite states like the bi-stable states but much smaller in amplitude. The ensemble-averaged pressure from sampling times as low as one second becomes a constant no matter the plasma actuation is steady or unsteady. However, the phasedlocked average of plasma duty cycle requires much more sampling time to reach a limit. Nomenclature Cn = yawing moment coefficient about cone base, yawing moment/q∞SD Cp = pressure coefficient CY = overall side-force coefficient, overall side force/q∞S CY d = ensemble-averaged local side-force coefficient, local side force/q∞d cY d = phase-locked averaged local side-force coefficient D = base diameter of circular cone forebody d = local diameter of circular cone forebody F = frequency of a.c. voltage source f = frequency of duty cycle L = length of circular cone forebody q∞ = free-stream dynamic pressure Re = free-stream Reynolds number based on D T = period of duty cycle t = time of duty cycle U∞ = free-stream velocity Vp−p = peak-to-peak voltage of a.c. voltage source w = input power of a.c. voltage source