Assessment of Numerical Methods for Ship Airwake Simulations with Unsteady Atmospheric Boundary-Layer Effects

This paper discusses two CFD approaches to ship airwake simulation in unsteady atmospheric boundary layers (ABL) - Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Large-Eddy Simulation (LES) - for the advancement of the computational environment toward numerical determination of helicopter launch and recovery envelopes. The general numerical methods of each approach are detailed, including the equations, turbulence closure models, and required numerical discretization schemes. The two methods are evaluated for a non-ABL inflow case against experimental data for the simple frigate shape 2 (SFS2) taken at the Naval Surface Warfare Center, Carderock Divison (NSWCCD). Velocity versus vertical height in the ship airwake at eight sampling locations over the flight deck for both the URANS and LES numerical methods show good agreement with experimental data in the case of a headwind. The numerical methods discussed are extended to simulate ship airwakes including unsteady atmospheric boundary-layer effects. Additionally, the versatility of each method is demonstrated through the application to off-bow winds and varying levels of ship geometry complexity.