Fluidic Injection on a Supersonic Jet at Various Mach Numbers

Fluidic injection on a supersonic jet operating at design and imperfectly expanded conditions was investigated. The nozzle simulates tactical military jet nozzles with conical sections and 12 pairs of fluidic injectors were incorporated into the nozzle lip. The effect of fluidic injection was studied at the design Mach number of 1.56, underexpanded, and overexpanded conditions. Far-field acoustic and flowfield measurements are presented for various injector momentum flux ratios at different jet operating conditions. The three velocity components were measured in cross-stream planes to compute the mean velocity and turbulence kinetic energy. At all conditions, increasing the injector momentum flux ratio resulted in greater reduction of noise. At overexpanded conditions, overall reduction up to 4 and 3 dB was observed at forward and downstream angles, respectively. At nozzle design conditions, up to 15 dB reduction in shock noise was observed in the narrowband spectra. Fluidic injection was more effective than chevrons at design and overexpanded conditions, though not at underexpanded conditions. Noise reduction was strongly dependent on the initial streamwise vorticity strength and the persistence of the vortices in the jet.