Effect on Radiated Sound Due to Fluidic Injection at Several Downstream Locations in a Mach 0.5 Jet

We experimentally investigate the effects of fluidic injection on a Mach 0.5 jet at several downstream locations by focusing on the radiated sound. Three streamwise locations are selected according to the expected growth rate of the underlying shear layer instability wave: first, immediately downstream of the nozzle exit with the shear layer being the thinnest, second, at the potential core breakdown location with the instability waves having reached their peak and the third at downstream of this breakdown. The new fluidic injection system is used to perform steady injections at these locations via two fluidic injectors located diametrically opposite, with different injector mass flow ratios. The measured acoustic spectra show significant reductions in peak sound, up to more than 6 dB at the peak downstream angle of 30◦ with the jet downstream axis, while the sound at the sideline and upstream angles is reduced even further.