Active Control of Noise in Supersonic Rectangular Jets

High-speed jets generate extreme levels of noise, resulting in hazardous working conditions for crew, and detrimental effects on aircraft structure and environment. Using large-eddy simulations, we explore the noise-reduction potential of Localized Arc Filament Plasma Actuators (LAFPA) based active control, in the context of a Mach 1.5 perfectly expanded jet exiting a 2:1 aspect ratio rectangular nozzle. LAFPA control at Strouhal number (St)=1 and duty cycle of 50%, decreases the peak far-field noise levels by attenuating radiated energy within the spectral bands, St=0.2-0.4 and St=0.65-0.8. The effect of control is most visible on the major axis plane. LAFPA actuation induces adjacent horseshoe vortices staggered in the streamwise direction within the shear layer of the jet. The resulting manipulation of coherent structures reduces the supersonic component of energy within the column mode of the jet by redistributing it into a higher spectral band at St=1. Further, LAFPA promotes azimuthal percolation of energy into the first and second helical modes, thus reducing the overall radiative efficiency of the jet. An energy analysis confirms the effectiveness of LAFPA control by identifying the weaking of noise-causing vortex intrusion mechanisms in the potential core of the jet.