Effect of Nozzle–Plate Distance on Acoustic Phenomena from Supersonic Impinging Jet

Abstract

For an adequate understanding of the broadband acoustic phenomena generated by a rocket exhaust jet impinging on a flame deflector, this study experimentally clarifies the factors that cause the difference in the broadband acoustic field of a supersonic ideally expanded jet impinging on an inclined flat plate for various nozzle-plate distances. According to previous studies, there are two possible factors: the Mach waves, which are radiated from the free-jet region and reflected by the plate, and the acoustic waves generated in the impingement region. To distinguish the effects of these factors, this study compares the following three results: the overall sound pressure level distribution, images extracted from the schlieren visualization movies using acoustic-triggered conditional sampling, and tracing lines of the acoustic intensity vectors of the Mach waves. The results reveal that the nozzle-plate distance affects the fraction of the Mach waves that are generated in the free-jet region and reflected by the plate, resulting in a higher overall sound pressure level in the upstream direction for larger nozzle-plate distances. It is concluded that the location of the plate relative to the source region of the Mach waves significantly affects the acoustic phenomena, owing to the variation in the nozzle-plate distances.

Flow and Acoustic Fields of Rocket Jets Impinging on a Perforated Plate

“…III.A. A wall jet has similarly been observed for supersonic jets impinging on an inclined plate in the experiments of Akamine et al [39,40] for M j 1.8 and in the simulations of Nonomura et al [41,42] for M j 2. In these studies, Mach waves were found to be emitted by the wall jet, due to the supersonic convection velocity of the jet turbulent structures.…”

Coupled CFD-CAA Simulation of the Noise Generated by a Hot Supersonic Jet Impinging on a Flat Plate with Exhaust Hole

“…Then, some investigations have been performed on impinging jets on an inclined flat plate [5]. Effects of nozzle-exit distance and tilt angle have been investigated [6]. Next step was to consider a horizontal flat plate [7] equipped with an exhaust hole [8,9].…”

Numerical study for the flame deflector design of four-engine liquid rockets

“…The result evidenced that the impingement angle is a vital factor in the reduction of sound pressure near the rocket. In recent years, Akamine et al (2018) analysed the influence of different nozzle-plate distances on the expand jet impingement flow field. Their conclusions state that the separation distance had a considerable effect on the structure of the flow field, which was in turn generated in the free jet region and reflected by the deflector surface.…”