Investigation of vortex-induced vibrations to compare Reynolds-averaged Navier-Stokes and detached-eddy simulations

We investigate vortex-induced vibrations (VIV) of a vertically spring-suspended NACA0021 airfoil at very high angles of attack of 60° and 70° at a chord Reynolds number of 2.7 × 105 by comparison of two-dimensional Reynolds-averaged Navier-Stokes (RANS) and three-dimensional delayed detached-eddy (DDES) simulations. For the non-moving airfoil, the simulated flow field is already highly unsteady due to pronounced wake vortex shedding with a dominant Strouhal number of Sr ≈ 0.19 and with large qualitative differences in the spectral content of RANS and DDES integral forces. These differences decrease significantly when the airfoil is conducting sine-like motions either by prescribed forcing or via free fluidstructure interaction. No major differences occur between RANS and DDES in the resulting maximum VIV limit-cycle amplitudes under lock-in conditions, while the lock-in frequency range is slightly narrower for DDES. During lock-in a remarkable reduction in the turbulent intensity can be observed in the scale-resolving simulations.