A Study of the Correlation of Large-Scale Structure Dynamics and Far-Field Radiated Noise in an Excited Mach 0.9 Jet

Abstract

The main goal of the present work is to excite various instabilities of an axisymmetric Mach 0.9 jet with a Re_D of 0.76 × 10⁶, track the ensuing large-scale structures/instability waves, and investigate relations between the dynamics of these structures and the far-field sound. The jet was excited over a large range of Strouhal numbers and several azimuthal modes by eight localized arc filament plasma actuators, equally spaced around the circumference of the nozzle, near the nozzle exit. The flow field and far-field noise were investigated using particle image velocimetry and a three-dimensional array of 12 microphones at 30° polar angle to the downstream jet axis. The microphone array results show that the high amplitude noise radiated to 30° polar angle is originated just downstream of the end of the potential core, in agreement with our previous results and the results in the literature. The streamwise noise source distribution was only sensitive to azimuthal modes around the jet preferred mode. Otherwise, the general trend was that forcing the jet at low Strouhal numbers moves the distribution upstream compared to the baseline jet, and at high Strouhal numbers results in a source distribution similar to the baseline jet. ***Conditionally-averaged PIV data were used to relate the flow dynamics and noise sources. The growth, saturation, and decay of the conditionally-averaged velocity fluctuations along the jet centerline correlate well with the far-field noise and the noise source distribution estimated using the microphone array. For m = 0 mode excitation around the jet column Strouhal number, the conditionally-averaged streamwise velocity fluctuations correlate well with the noise source distribution. While for m = 1, the correlation is best with the conditionally-averaged cross-stream fluctuations.