Numerical Investigations of Dynamic Stall on a Rotor with Cyclic Pitch Control

Abstract

Numerical computations of three-dimensional dynamic stall on a two-bladed model rotor (R = 0.65 m, M_75 = 0.21, Re_75 = 3.5 × 10*5) with 1/rev cyclic pitch control are presented and compared to experimental surface pressure and particle image velocimetry data. In addition to unsteady Reynolds-averaged Navier-Stokes (URANS) simulations using the finite-volume flow solvers FLOWer and TAU, a delayed detached-eddy simulation (DDES) with Menter shear-stress transport (SST) as underlying Reynolds-averaged Navier-Stokes (RANS) model is carried out with FLOWer. Facing dynamic stall and flow separation, the DDES reproduces high-frequency load fluctuations, cycle-to-cycle variations, and small-scale vortical structures observed in the experiment, unlike the URANS results. However, common hybrid RANS/large-eddy simulation issues - grid-induced separation (GIS) and the gray area problem - play a role in this DDES and influence loads severely. FLOWer SST simulations yield load peaks of the same magnitude as individual, non-phase-averaged measurements. With TAU SST, the dynamic stall event is delayed and weakened compared to FLOWer SST and experimental results. FLOWer and TAU results using the Spalart-Allmaras turbulence model are fairly comparable but in bad agreement with the experiment at the outboard station at r/R = 0.77, where they exhibit no dynamic stall at all.