Characterisation of the turbulent boundary-layer wall-pressure spectrum for a ship hull

For a new generation of fast ships, the hydrodynamic noise sources represent an important item to be considered for a correct evaluation of the noise transmitted on board and its reduction is necessary to improve the comfort of passengers and crew. In particular, the pressure fluctuations induced on the ship hull by the turbulent boundary layer are investigated in this paper. The full scale characterization of the pressure fluctuations would imply expensive and cumbersome measurements on the real ship during navigation or, on the other hand, direct numerical simulations of the fluid flow around the hull that are not yet possible with available computational resources. In this paper a procedure able to estimate the full scale pressure spectra based on a combination of model scale measurements and direct numerical simulations is presented. The key of the method is the selection of scaling laws for the pressure spectra obtained from model scale measurements, that in this way can be recast as a universal curve.The scaling factors are defined as suitable combinations of the mean flow local parameters. Once a scaling law for all the frequency regions of the spectrum is established, the universal curve is simply re-scaled by the mean flow parameters obtained by direct numerical simulations of the boundary layer around the hull at full size to get the final spectra. Numerical simulations are made using 3D N-S averaged equations with taking into account an unsteady behaviour of the free surface around the hull. The advantage of this procedure is that only mean properties of the flow are requested, thus implying a dramatic decrement of time computation.In particular, the present procedure is applied to estimate the characteristics of the wall pressure spectrum over the hull of an high speed vessel.