Statistics and spatio-temporal correlations of wall pressure fluctuations beneath an impinging round jet boundary layer

We present here synchronized measurements of an incompressible impinging round jet turbulent boundary layer and an hydroacoustic wall pressure array. Data was collected in a 1.2m x 0.6m water tank with flow driven by a 90-gph circulation pump through an axisymmetric round jet with a 10:1 contraction ratio and 14° convergence angle mounted 45° normal to the surface. Two-component planar flow fields were obtained via particle image velocimetry (PIV) using a 70mJ 532-nm laser at 15Hz and image pairs from an Imperx CCD camera. Simultaneous acoustic wall pressure was obtained using a linear array of five equally spaced flush-mounted piezoelectric sensors covering a spatial range of ~14 nozzle diameters from the stagnation point.

Spatio-temporal correlations between boundary layer coherent structures and acoustic wall pressure data were computed, and turbulent convection velocities from PIV data were found to be in agreement with pressure signals propagating along the sensor array. A cross-wavelet analysis of wall pressure fluctuations was performed to identify dominant modes of the high- and low-frequency components. Spectral properties of wall pressure, including probably density functions and higher order moments, were computed and used to identify hydroacoustic and hydrodynamic contributions. The results are important for future signal processing efforts to isolate flow-induced noise from a target signal and for future flow control strategies. [Work supported by the Office of Naval Research.]