The full spectrum of broadband shock cell noise

Abstract

Broadband shock cell noise has been studied by numerous investigators since the work of Harper-Bourne and Fisher (1973). This noise component radiates in the upstream direction together with another noise component, the fine scale mixing noise. In measured noise spectra, broadband shock cell noise shows up as a small peak protruded up from a broad background noise. The spectral shape of the peak has been studied by Tam (1990) and Kuo et al. (2015). Good agreements are found between predictions and measurements. This situation begs the question of the shape of the full noise spectrum. The answer lies in devising a way to separate the two noise components. Here, this is done at the raw data level. We know broadband shock cell noise is generated by the interaction between large turbulent structures and shock cells whereas mixing noise is generated by fine scale turbulence. One, therefore, expects a scale separation between the two noise components. Broadband shock cell noise sound pulses are expected to have a longer duration or larger pulses while turbulent mixing noise much shorter pulses. This idea has now been implemented on a set of F-18E noise data at 28 degrees. Results and relevant details will be reported.