On computational simulations of dynamic stall and its three-dimensional nature

In this paper, we investigate the three-dimensional nature of dynamic stall. Conducting the investigation, the flow around a harmonically pitching National Advisory Committee for Aeronautics (NACA) 0012 airfoil is numerically simulated using Unsteady-Reynolds-Averaged Navier-Stokes (URANS) and multiple detached eddy simulation (DES) solvers: the Delayed-DES (DDES) and the Improved-DDES (IDDES). Two- and three-dimensional simulations are performed for each solver, and the results are compared against experimental measurements in the literature. The results showed that three-dimensional simulations surpass two-dimensional ones in capturing the stages of dynamic stall and predicting the lift coefficient values, with a distinguished performance of the DES solvers over the URANS ones. For instance, the IDDES simulations, as an inherently three-dimensional solver, predicted the necessary cascaded amalgamation process of vortices to form the adequate strength of the dynamic stall vortex. This vortex size and timing provided accurate and sufficient suction that resulted in identical matching of the numerical and experimental lift coefficients at the peak value. Hence, the hypothesis that dynamic stall has a three-dimensional nature is supported by the superiority of the three-dimensional simulation in all aspects. In conclusion, it is found that dynamic stall is intrinsically a three-dimensional phenomenon.