Space-time characteristics of wall pressure fluctuations on the surface of flexible extended cylinder

Generation of the hydrodynamic or aerodynamic noise is a well-known problem for vehicles and structures moving in water or air media. Therefore, predicting and controlling the properties of the turbulent hydrodynamic pseudoacoustic sources is of great importance. This paper presents the results of an experimental study of the cross-correlations and cross-spectra of wall pressure fluctuations on the surface of a longitudinally streamlined flexible cylinder. The degree of conversion of flow energy into the energy of the wall pressure fluctuation field is shown to be limited by a certain threshold. Its value corresponds to the ratio of the root-mean-square wall pressure fluctuation to the dynamic pressure of the order of 0.01 on a hydraulically smooth streamlined surface under a turbulent boundary layer with zero pressure gradient. The space-time correlation of wall pressure fluctuations along the generatrix of a flexible extended cylinder decreases with increasing distance between observation points, and the maximum values of the cross-correlation are observed for longer delay times. Convection of coherent vortex structures over the streamlined cylinder surface leads to an increase in the coherence levels of the wall pressure fluctuation field. Moreover, changes in the phase spectrum presented by sloping curves are observed. Their slope decreases with increasing convective velocity. The rate of degeneration of the maximum values of the space-time correlation coefficient in a wide frequency range on a flexible cylinder is higher than on a plate. Small-scale vortices that generate high-frequency pressure oscillations degenerate faster and are transported more slowly than large-scale coherent vortical structures from the outer region of the boundary layer. The obtained results are useful for the designers of the towed linear receiving hydroacoustic arrays.