Computations of Separated Flows with a Hybrid RANS/LES Approach

In an effort to accurately compute nacelle stall processes, the research unit FOR1066 (Simulation of Wing and Nacelle Stall) has been working extensively on the development of advanced simulation methods. Due to the high dependency of the separation aerodynamics on the turbulent structures developed within the boundary layer, embedded LES methods appear promising to reliably compute such processes. Nevertheless, these approaches are characterized by exhibiting a very long “grey area“ (also known as adaptation distance) that may lead to the degradation of the whole solution. To shorten this adaptation distance, an advanced synthetic turbulence generator is implemented that forces the development of resolved turbulence at the inlet of the LES domain. The implementation is accessed for a zero pressure gradient flat plate, the HGR-01 airfoil, and a subsonic flow-through nacelle case. The numerical results are validated against experimental data and compared with numerical results without applying synthetic turbulence forcing. Results show that the implementation considerably reduces the required adaptation distance enhancing the overall solution. However, the success of the computation also depends on the solver numerical settings and the grid resolution.