Assessment Of Delayed Detached-Eddy Simulation Of Dynamic Stall On A Rotor

High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) and Menter-SST delayed detached-eddy simulations (DDES) of dynamic stall on a rotor with cyclic pitch control are presented and compared to experimental surface pressures and particle-image-velocimetry (PIV) data. Before the dynamic-stall event, the DDES suffers from modeled-stress depletion (MSD) leading to grid-induced separation (GIS) due to a breakdown of the boundary-layer shielding function f(d). Combined with the "grey-area" problem, this leads to severe erroneous load peaks. After dynamic stall, flow is completely separated and only DDES shows realistic small-scale, incoherent vortical structures. Two approaches are investigated to eliminate MSD/GIS: Firstly, increasing the empirical constant C-d1 of the f(d) function to 30 basically eliminates GIS. Secondly, a non-local, grid-independent vorticity-integrated algebraic DES, which replaces the f(d) function, is introduced that provides robust boundary-layer shielding and enables the LES mode in case of massive flow separation.