An Experimental and Numerical Study of Sound Propagation from a Supersonic Jet Passing through a Rigid-Walled Duct with a J-Deflector

Abstract

In recent years there has been considerable interest in the design of exhaust ducts for jet noise mitigation systems for launch vehicles devoid of water injection. Clean (dry) launch pads with ducted exhausts are preferable to those fitted with water deluge systems for sound suppression with regard to operational costs and the frequency of launches. Thus, the overall process of sound emission from partially ducted rocket exhausts is of great practical interest in the understanding of sound suppression systems for launch vehicles. Detailed knowledge of the behaviour of the sound radiation from these ducted exhausts is useful in the design and optimisation of the sound suppression systems. The totality of the far-field sound from ducted exhausts is composed of the transmission of sound from the free supersonic jet (upstream of the duct inlet) to the far-field, the transmission of sound within the duct, and the radiation of sound from the duct exit and the subsonic jet (exiting the duct) to the far-field. Recent experiments on enclosed ducts by Kandula et al. have indicated that the jet confinement has a significant effect on sound emission and directivity, suggesting that the duct modifies the sound generation and propagation. According to Sir James Lighthill, noise generation from subsonic jets is mainly due to turbulent mixing, and is comprised of the contributions of large-scale and fine-scale struc-