Operational Control of Mixing Enhancement and Far-Field Jet Noise Suppression Using Downstream Fluidic Injection

A novel fluid injection scheme is analyzed for its ability to suppress the far-field jet noise using multiple radial microjets placed downstream from the nozzle exhaust. Contrary to other previous research studies, which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which subsequently breaks down into streamwise vortices as the microjet bends and follows the flow direction. Microjet injection pressure and angle of injection play a crucial role in determining the jet trajectory, penetration, and the strength of the CVP formed. The effect of these parameters on the far-field acoustic radiation is evaluated in this study. Detailed large eddy simulations are performed for a nozzle–injector setup operating at Mach 0.9 jet with Reynolds number ≈10⁶ to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet.