CFD Simulations of Unsteady LHA Ship Airwake in OpenFOAM

Sammanfattning: Extensive research in the past two decades has shown that flow around the sharp edges of bluff bodies, such as the superstructure of a ship, can cause large scale shear-layer separations with increased turbulence, generating a highly unsteady flow in the airwake region. Such separations affect the control margins and handling loading of a rotorcraft, mainly if operating from the vicinity of a flight deck, and therefore negatively influence the rotorcraft operating limits, which is one of the main reasons for the study of ship airwakes. Current work focuses on CFD analysis of the US Landing Helicopter Assault (LHA) ship airwake, both through Reynolds-Averaged Navier Stokes (RANS) simulations and Improved Delayed Detached-Eddy Simulations (IDDES), particularly focusing on IDDES. Simulations involved an increasing number of grid resolutions (with a total of 7) for thorough convergence and grid independence study of the inherently turbulent flow, with the highest resolution being the largest computation to date of the LHA ship airwake. Computations were undertaken using the open-source unstructured grid Navier-Stokes CFD software OpenFOAM. The work thoroughly discusses the results for 7 independent wind-over-deck (WOD) angles and wind velocities of 30 knots, and shows quantitative data and analysis of numerous flow quantities.