Wall pressure models for non-equilibrium boundary layers

In the last years, several experimental campaigns have been devoted to understand the characteristics of the noise induced by turbulent flow around the hull of surface and underwater marine vehicles. In particular experimental setups and test campaigns have been designed to measure, mostly in towing tanks, wall pressure fluctuations beneath non-equilibrium boundary layers. These last can be the result of free surface effects, surface curvature and transitional phenomena. In general, due to the complicated history of the flow about a ship hull, equilibrium conditions are rarely achieved. Experimental data concerning models of a bulbous bow of a military vessels, a catamaran and an underwater vehicle characterized by a bluff geometry in its fore part are used in this work to analyze wall pressure beneath non-stationary and inhomogeneous boundary layers. The results are compared with some available literature pressure data relative to different flow conditions and with other measurements acquired in the towing tank for almost equilibrium boundary layer. The possibility to provide case independent analytical descriptions of the pressure field for the different frequency ranges of interest is also analyzed through the application of existing and new formula.