Acoustic and flow fields of an excited high Reynolds number axisymmetric supersonic jet

An axisymmetric perfectly expanded Mach 1.3 jet, with a Reynolds number based on the nozzle exit diameter (Re(D)) of 1.1 x 10(6) and turbulent boundary layer at the nozzle exit, was excited using localized arc filament plasma actuators over a wide range of forcing Strouhal numbers (St(DF)). Eight actuators distributed azimuthally were used to excite azimuthal modes m=0-3. Far-field acoustic, flow velocity and irrotational near-field pressure were probed with a three-fold objective: (i) to investigate the broadband far-field noise amplification reported in the literature at lower speeds and Re(D) using excitation of m = 0 at low StDF; to explore broadband far-field noise suppression using excitation of in = 3 at higher St(DF); and (iii) to shed some light on the connection between the flow field and the far-field noise. The broadband far-field noise amplification observed is not as extensive in amplitude or frequency range, but still sufficiently large to be of concern in practical applications. Broadband far-field noise suppression of 4-5 dB at 30 degrees polar angle peak frequency, resulting in approximately 2 dB attenuation in the overall sound pressure level, is achieved with excitation of in = 3 at St(DF) similar to 0.9. Some of the noteworthy observations and inferences are (a) there is a strong correlation between the far-field broadband noise amplification and the turbulence amplification; (h) far-field noise suppression is achieved when the jet is forced with the maximum jet initial growth rate frequency thus limiting significant dynamics of structures to a shorter region close to the nozzle exit; (c) structure breakdown and dynamic interaction seem to be the dominant source of noise; and (d) coherent structures dominate the forced jet over a wide range of St(DF) (up to similar to 1.31) with the largest and most organized structures observed around the jet preferred mode St(DF).