Increase and decrease of the noise radiated by high-Reynolds-number subsonic jets through plasma synthetic jet actuation

Abstract

Since the discovery of the existence of largescale structures in high-Reynolds-number free shear flows [1] and their role in the radiation of noise to the far field [5], the control of their dynamics has been an important topic for the aeroacoustic community. In the past decades, active noise reduction techniques have been extensively investigated. Continuous fluidic microjets have shown to decrease the far-field overall sound pressure levels of about 1.5 dB in the aft region (Θ = 30°) of high-Reynolds number high-subsonic jets [3]. In order to prevent any thrust penalty due to continuous air injection, other types of actuation are currently being investigated. Recently, Samimy et al. [6] have developed localized arc filament plasma (LAFPA) actuators for jet noise control. Applied on a Mj = 0.9, they reported jet noise reduction in the aft region of −0.5 dB to −1.0 dB for actuation Strouhal numbers between 1.5 and 2.0. The present study investigates the use of Plasma Synthetic Jet (PSJ) actuators for the active modification of the noise radiated by high-Reynolds-number subsonic jets. Experimental setups. A. PSJ actuator The Plasma Synthetic Jet (PSJ) actuator has been developed at ONERA in the last decade as an actuator providing high control authority over high-speed and high-Reynolds-number flows [2]. Similar to the SparkJet developed at Hopkins University [4], it relies on an energy deposition in a cavity through electrical breakdown between too electrodes, shown in figure 1a. High temperature and pressure rise in the cavity generates a transient exhaust of air through an orifice of the cavity. Equilibrium in the cavity is then retrieved after a suction phase. Depending on the electrical and geometrical design, this actuator may be driven at frequencies up to 4 kHz. For moderate actuation frequencies, transient exit velocities of about 150 m/s can be reached. [...]