Near-field acoustical array measurements of an impinging supersonic jet

Abstract

Impingement significantly alters the rocket plume in the near-launch pad environment, which in turn affects the acoustic radiation. Prior laboratory measurements of an unheated, Mach 1.8 ideally expanded jet impinging on 45-degree inclined flat plate were carried out using a microphone that was moved within a relatively dense grid [Akamine et al., AIAA J. 53, 2061–2067 (2015)]. A multi-institution collaboration by the authors was begun in order to conduct array measurements of the acoustic radiation from both impinging and free jets. Measurements comprised a total of 42 measurement channels located within 40 nozzle diameters. An array of two-dimensional microphone probes was placed so as to examine the transition from the hydrodynamic near field to the acoustic radiation. A scanning linear array of microphones and a stationary polar array were also designed to enable beamforming, cross correlation, and partial field decomposition. This paper describes the jet facility, experiment design, and initial analyses conducted on the data collected. [Measurements supported by the Japanese Society for the Promotion of Science.]