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High-order detached eddy simulation of unsteady flow around NREL S826 airfoil

Delayed detached eddy simulation (DDES) has been a common approach for unsteady turbulent flow problems, but it has several weaknesses which limit its use to detached flows. On the other hand, some enhancements introduced recently have made it possible to apply to attached flows as well. In the present investigation, flow with relatively low Reynolds numbers of 100, 000 and 145, 000 around NREL S826 airfoil is simulated using DDES models with two different length scale definitions: standard length scale and shear-layer-adapted length scale (SLADDES). The solver, originally developed for aeroacoustic simulations, features fourth-order spatial accuracy enhanced with symmetry-preserving and dispersion-relation-preserving characteristics. Simulations are done at various angles of attack around stall regions. Results are compared with other simulations and measurements. The present results indicate that SLADDES accelerates transition from modeled turbulence mode to resolved turbulence mode even in attached flows. Consequently, SLADDES shows aerodynamic results in better agreement with the experiments than the standard DDES, and allows coarser grids thanks to low sensitivity to spanwise grid spacings. Moreover, it appears that both DDES and SLADDES approaches benefit from the low dissipation, low-dispersion, and high-order scheme of the solver.