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Stochastic disturbances, induced by plasma actuator in a flat plate boundary layer

Mechanism of hydrodynamic noise generation in subsonic flat plate boundary layer by barrier discharge plasma actuator is described. The origin of the pulsations is an inscintric unsteadiness of the discharge structure caused by wandering of the microdischarges. Statistics of discharge wandering is obtained from discharge light emission. Propagation of the disturbances in slightly unstable Blasius boundary layer is studied both experimentally and numerically. It is demonstrated, that the discharge-induced noise can be modeled as a sum of delta-correlated localized boundary layer forcing events, with each event represented by the region of longitudinal and transversal force. Discharge-induced disturbances in the boundary layer undergo three main stages as they move downstream: streak-like structures in the near field, oblique wave fans and eventually a plane Tollmien-Shllichting wave. A simple statistical model, describing the dependency of the pulsations power on actuator driving frequency and voltage, is proposed.