On the spectral shape and a second component of broadband shock-cell noise

Abstract

It is known that broadband shock-cell noise of an imperfectly expanded supersonic jet radiates primarily in the upstream direction. In addition to broadband shock-cell noise, fine scale turbulent mixing noise is also a dominant component in the upstream direction. As a result, broadband shock-cell noise, generally, appears as a small peak protruded above a broadband noise background. For this reason, the complete spectral shape of broadband shock-cell noise has not been found. The first objective of this investigation is to determine the full spectral shape of broadband shock-cell noise. In the course of carrying out this effort, unexpectedly, we found compelling evidence that there is a second component of broadband shock-cell noise. The two broadband shock-cell noise components are generated by two different sources and mechanisms. The quasi-periodic shock cells in the jet flow play a crucial role in their generation. All these findings are reported in this paper.