Cross-Correlation Analysis of Flow Noise with Fluid Dilatations as Source Fluctuation

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Abstract
A recently developed diagnostic technique for aerodynamic noise involves cross correlation between various types of source fluctuation and the resulting radiated sound [T. E. Siddon, Int. Congr. Acoust. 7th (1971)]. The technique yields explicit quantitative information on the volume distribution of source strength, the spectrum from unit volume, and the local correlation volume. Following Ribner's dilatation model of jet noise, the present paper considers “pseudosound” pressure as the source fluctuation. By moving a single probe around in the jet and cross-correlating with the farfield radiation, the character and distribution of the basic pressure sources is obtained. Preliminary experiments in a model air jet indicate difficulties arising from aerodynamic and acoustic contamination of the correlation functions. Special pressure probe configurations are described which minimize this contamination.

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