An Experimental Study on Transitional Boundary Layer Excitation on a Bulbous Bow of a Fast Ship

The present paper deals with the results of an experimental campaign aimed at characterizing the wall pressure fluctuations (WPF) beneath transitional boundary layer acting along the bulbous bow of a fast ship. The measurements were performed for three different velocities, corresponding to a variation of Reynolds numbers between 9.1 × 105 and 6 × 105. The acquired pressure signals are characterized by the presence of both turbulent bursts, with high frequency fluctuations, and low frequency fluctuations due to instability waves (Tollmien-Schlichting waves) in the laminar portion. The study focuses on three aspects: implementation of a new algorithm to detect turbulent bursts from wall pressure signals, identification of scaling laws for the auto spectral density of WPF in the transition process and characterization of the time-evolution of the their spectral distribution based on Pseudo Wigner Ville distribution.