Pressure cross spectra in turbulent boundary layers in water

The spectrum (power spectral density) of the vibration level for any linear system can be found by integrating the product of the cross spectrum of the excitation with the cross frequency response functions of the system over the area on which the excitation is acting. Measurements of the auto and cross spectra of the wall pressure fluctuations in a water tunnel are presented. It is shown that the cross spectra cannot be expressed as a product of functions of the streamwise and transverse coordinates alone but must include interaction terms. One possible parametric approximation is suggested.