Spectral characteristics of wall pressure fluctuations for surface ships

Wall pressure fluctuations generated by the turbulent boundary layer (TBL) which extends on the wall of moving vehicles, play an important role in the mechanism of noise generation through fluid-structure coupling. In the case of marine applications, the calculation and the suppression of the radiated noise is crucial to ensure sonar efficiency as well as to improve the confort level on board new high speed vessels for passenger transportation. The studies performed in this field, most of them devoted to aeronautical applications and based on the analysis of experimental data, deal with equilibrium flow for which scaling laws for the power spectral density and theoretical models for the cross spectral density are available. The problem in the case of marine vehicles presents some peculiarities because of pressure gradients due to both free surface and hull curvature. Their effects on wall pressure spectra are in this work analyzed comparing pressure experimental data measured in different locations along the hull where favorable, adverse and zero pressure gradients are present. These particular zone are identified by analyzing the mean velocity and pressure field obtained by RANS numerical simulations. The results of this analysis provides interesting information on the characteristics of wall pressure spectra and on the validity of the scaling laws for the power spectral density in the presence of pressure gradients.