Supersonic jet noise mitigation by angled tab perforation

Abstract

Supersonic jet noise, a significant concern in military and civilian aerospace due to its impact on aircraft operability, environmental compliance, and community noise standards, drives the need for studies on jet mixing to optimize processes and reduce noise emissions effectively. This study presents the design and development of a Mach 1.6 nozzle, designed to evaluate the jet decay, directional spread and noise attenuation character. Incorporated at the nozzle exit are two rectangular tabs, with perforation angles of zero and 30 degrees. These tabs, with a blockage ratio of 0.09, are strategically positioned to modify the exhaust flow pattern. Experimental analyses, inclusive of jet decay and acoustic assessments, were conducted at a nozzle pressure ratio of 4.25, corresponding to optimal expansion conditions. Observations were made on the centerline pressure decay along the jet axis and the lateral jet spreading for baseline and controlled jets. Utilizing the Schlieren optical method, the shockwave structures were visualized to understand the flow physics. The results indicated a substantial reduction in the length of the potential core, amounting to 65.13% and 80.76% for zero- and thirty-degrees perforation angles, respectively, compared to an unmodified baseline jet. Moreover, as compared to the baseline jet the 30 degrees perforation configuration demonstrated a significant 9 dB reduction in jet noise.