DES and RANS of unsteady free-surface wave induced separation

A general-purpose unsteady Reynolds-averaged Navier-Stokes (URANS) research code CFDSHIP-IOWA developed for ship hydrodynamics application is extended for detached eddy simulation (DES) capability. CFDSHIP-IOWA uses surface-tracking free-surface model, k-ω turbulence model, and high performance computing. Both 2 ^nd and 3 ^rd order upwind biased scheme for spatial derivatives were applied for URANS while 3 ^rd order upwind biased scheme used for DES. DES extensions are based on the blended k-ω model by modifying the length scale in the k equation and validated with surface piercing NACA 0024 benchmark, including IIHR towing-tank EFD data and concurrent URANS. Domain and grid convergence studies were conducted for 2 ^nd order RANS. 3 ^rd order RANS was also studied on a coarse grid and a 3 ^rd order DES was conducted on both coarse and medium grids. Statistical analysis of the results, including time history, running mean, and EFT of total drag and side forces, mean and RMS of wave elevations and pressure on foil surface, and unsteady 3D separation flow pattern are presented. Results show fairly good agreement EFD validation data for mean, RMS, and FFT frequencies for wave elevations and surface pressure; however, many modeling and numerical issues remain. Seemingly credible flow features of unsteady wave-induced separation have been simulated for the first time, which will be used to guide future PIV measurements.