LES of Shock Induced Separation

Abstract

The flow around a NACA 0012 section at transonic speed is investigated. The simulations are done at a Reynolds number of 3 · 10⁵. The angle of attack is 2.26 degrees and the Mach number 0.799. A laminar separation bubble is formed right after the shock due to the pressure rise caused by the shock, so called shock induced separation. The flow reattaches and undergoes transition to turbulence. A turbulent separated region forms at the trailing edge. This case is very challenging in terms of predicting transition and turbulence. The transition process starts inside the laminar separation bubble where low frequency instabilities are amplified. Only the dynamic LES-formulation can be expected to perform satisfactorily in this variety of situations. The subgrid-scale terms are accounted for in two ways; through a dynamic subgrid-scale (SGS)-model, where the divergence of the SGS-terms are expressed directly and independently and implicitly through the inherent dissipation of the numerical algorithm. Predictions for pressure distributions and skin friction coefficients are reported. The behaviour of the model parameters, both in time and space, are reported.