Tonal Noise Suppression of an Underexpanded Orifice Jet Upon Impingement Over Corrugated Geometries

Abstract

The current study investigates the noise generation of an orifice jet upon impingement over different corrugated geometries for different nozzle pressure ratios (NPRs). Semi-circular corrugations of different pitch lengths are considered for this study. A comparison of corrugated geometries is made with the flat plate. A standoff distance of 3.5 times jet diameter is considered during the experiment. The noise propagation at the far-field is observed using a far-field microphone. Several tones and their harmonics of the feedback loops established between the orifice exit and the plates are analyzed. The acoustic spectra show that the corrugated geometries emit less noise at subsonic speed compared to supersonic speed. A reduction of overall sound pressure level (OASPL) up to a range of 3–8 dB is observed for the corrugated plate compared to the base plate at the subsonic range. The tonal noise is reduced for the corrugated geometries at all NPRs. The wavelength of the primary tones is compared with the pitch length of semi-circular corrugations. Schlieren images show the presence of the acoustic feedback loop and standing waves near the impingement region for the flat plate. The flow field in between the semi-circular corrugations is analyzed by solving the large eddy simulation. The directivity study shows a reduction in OASPL value at the upstream direction at NPR 4 and 4.8 for the corrugated geometries.