Optimization in frequency characteristics of an oscillating dielectric barrier discharge plasma actuator

Frequency characteristics of an oscillating plasma actuator are investigated by phase-locked particle imaging velocimetry and an analytical model is built on this basis to optimize the frequency characteristics. Experimental results show that effective near-wall oscillating flow can only be achieved at a modulation frequency below tens of hertz. Once beyond this range, the flow pattern transits rapidly from a periodic alternation of two opposite near-wall jets to a quasi-steady vertical jet, resulting in a sharp drop in spanwise oscillation strength. Although this performance deterioration at high modulation frequency can be partially recovered by increasing the voltage amplitude, its decay rate as reflected by the cut-off frequency changes marginally. In addition, an analytical model is derived from a simplified momentum equation, revealing that the cut-off frequency of an oscillating plasma actuator is determined by both the ground electrode width w_g and the maximum jet propagation distance within a half oscillation cycle, L_jet. Depending on how these two parameters compare with each other, three different working modes of the oscillating plasma actuator can occur. For the purpose of increasing the effective oscillating frequency of the plasma actuator in turbulent drag reduction applications, the geometrical and electrical parameters should be carefully selected to make sure the actuator works in modes 1 and 2, where the criterion L_jet > 0.5w_g is met.