Wall pressure fluctuations induced by turbulent boundary layers over surface discontinuities

An experimental investigation of wall pressure fluctuations generated by turbulent boundary layers over surface irregularities has been conducted in a backward–forward-facing step geometry simulating a large aspect-ratio cavity. This simplified incompressible flow model was designed to reproduce geometrical discontinuities present, for example on an aircraft fuselage, and responsible for interior noise generation. This study considers the effects of the main dimensionless parameters, such as the Reynolds number, the normalized incoming boundary layer thickness and its space averaged turbulence intensity, on the Sound Pressure Levels (SPL) and auto-spectra frequency estimates at the wall. Phase averaged temporal quantities are obtained by the application of a wavelet based auto-conditioning method and by velocity/pressure conditional statistics and cross-correlations. This analysis clarifies some relevant properties of the wall pressure fluctuations in the two-steps configuration. Satisfactory scaling for both the SPL and the frequency spectra by dimensionless parameters are obtained and empirical correlations which might be useful for predicting wall pressure properties in practical applications are derived.