Surface high frequency dielectric barrier discharge (HF DBD) was used to reduce flow-induced noise, radiated by circular cylinder in cross flow. Effect of HF DBD actuators is studied for flow velocity up to 80 m s−1 (Reynolds numbers up to 2.18 · 105), corresponding to the typical aircraft landing approach speed. Noise measurements were performed by microphone array in anechoic chamber; averaged flow parameters were studied by particle image velocimetry (PIV). Actuator was powered by high-frequency voltage in hundreds kHz range in steady or modulated mode with the modulation frequency of 0.3–20 kHz (Strouhal number St of 0.4 to 20). It is demonstrated that upstream directed plasma actuators are able to reduce the vortex noise of a cylinder by 10 dB. Noise reduction is accompanied by significant reorganization of the wake behind a cylinder, decreasing both wake width and turbulence level. The physical mechanism related to broadband noise control by HF DBD actuator is also discussed.

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Nomenclature PVR= plasma vortex reactor HF = high frequency F HF = HF frequency F M = modulation frequency of HFD T i = pulse duration I = electric discharge current V = electric discharge voltage Q e = power input in plasma V x = axial flow velocity V t = tangential flow velocity P st = static pressure T g = gas temperature T R = rotation temperature T V = vibration temperature T e = electron excitation temperature T b = black body temperature Abstract Study of a longitudinal plasmoid in swirl flow is very important both for plasma aerodynamics and extra energy release 1-8, 10 . A longitudinal heterogeneous plasmoid structure and its dynamics in the swirl flow were studied in our previous works in detail 1-6 . The present work is a continuation of the previous ones. The non-equilibrium combined discharge (DC discharge + HF discharge) is used in this experimental work. A pulsed repetitive power pumping in the swirl flow is created by the combined discharge. The plasma created by this discharge can disturb the initial swirl flow. Plasma and airflow parameters are measured by different diagnostic instrumentation including a high-speed camera, electric and current probes, an optical spectrometer and etc. Following main new experimental and theoretical results are obtained in this work: a velocity distribution and a gas temperature distribution are measured in the swirl flow at different discharge and gas flow parameters. Detail optical spectra with a high resolution in a vortex longitudinal plasmoid created by the combined electric discharge are obtained. Processing of these spectra gives an important information about nonequilibrium processes inside the longitudinal plasmoid in the swirl flow. Obtained results are used in a theoretical model of plasma and a chemical kinetics in the vortex heterogeneous plasmoid created by the non-equilibrium DC discharge. Numerical results on a swirl flow structure and its evolution at plasma on are obtained and compared with experimental results.