Hybrid RANS–LES wake studies of an airfoil in stall

Numerical simulations of the flow about a NACA 0012 airfoil in low speed stall conditions are presented. The focus is set on the propagation of turbulence in the wake of the airfoil. The calculations were performed at a Mach number of 0.3, a Reynolds number of 6 million and an angle of attack close to maximum lift. The unstructured finite-volume solver TAU, which is developed by the German Aerospace Centre, was used to simulate the unsteady flow in the vicinity of the airfoil and its wake up to two chord lengths downstream. Hybrid turbulence models are used to represent the attached part of the boundary layer with the Reynolds-averaged Navier–Stokes equations (RANS) and the detached regions with large eddy simulation (LES). This enables a direct resolution of the large-scale turbulent movement in the separated regions and the wake behind the airfoil. The simulations were conducted on different meshes with increasing resolution. The capability of two hybrid RANS–LES models of detached eddy simulation type is investigated in representing the turbulent characteristics of the far wake. The influence of the mesh properties and the modeling approach is discussed. Hence the pressure spectra in the wake are compared to experimental data. Due to good agreement of the improved DDES results with the measurement data, the wake of the airfoil is evaluated over a long time period. The development of pressure and velocity spectra along the wake is discussed.

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