Ship airwake simulation background

From previous studies, it has been shown that the key feature of ship airwake flow is (1) a low Mach number (about 0.05), (2) inherently unsteady flow, and (3) large regions of separated flow. The large separated regions from superstructure sharp edges are quite difficult to capture accurately. In addition, the wind conditions over rough sea have to be considered, such as, the atmospheric turbulence boundary layer and the effect of the wind/ship speed ratio on the turbulence intensity and frequency shift. The wind direction can vary a great deal, since the air flow can impact the ship at any yaw angle. The complex ship geometry makes unstructured grid solvers and parallel computers a necessity.

In this paper, the ship airwake simulation is focused on the helicopter/ship interface problem. The flow impact on helicopter main blades includes mean flow velocity and spectrum of perturbation velocity. It is known that the mean velocity and large perturbations have a strong effect on engage/disengage. The perturbation velocity and its dominant frequencies from airwake turbulent and separated flow is also very important to flight simulators. Therefore, preliminary attempts at high order accurate ship airwake predictions have been made by solving a steady flow field with a well-developed CFD method (CFL3D) and a perturbation field with a high-order method. The result is high-order-accurate 3D simulations.