Flow Field and Spectral Characteristics of a Ship Airwake with Wave-induced Motions

A rotorcraft landing on a ship deck interacts with a highly unsteady aerodynamic environment due to atmospheric boundary layer turbulence and the unsteady airwake shed by the ship superstructure, which may be influenced by wave-induced motion of the ship. Applying PIV and LDV measurements on a 2-m-long ship model and DES numerical simulations using a dynamic overset grid technique, we consider the wind flow field over the ONR Tumblehome geometry with uniform inflow at a Reynolds number of 10⁶, with and without imposed pitch and heave motions derived from wave interactions. Whereas at Re=O(10⁴), discrete flow structures shed from the fore of the superstructure synchronize with arch structures to form a highly periodic shedding pattern over the landing deck, at Re=10⁶, the diminished scale of the fore structures and broader range of spatial scales makes the flow much more complex. Mean velocity fields and spectra in the vicinity of the landing deck are compared with and without periodic ship motions to provide insight into the dynamics of the airwake and the influence of ship motion.