Simulation of pressure and shock induced separation using DES implementations in the DLR-TAU Code
S. Illi, Th. Lutz and E. Krämer, Second Symposiom "Simulation of Wing and Nacelle Stall", Braunschweig, Germany, June 22nd - 23rd 2010
Although computational fluid dynamics made its way to become an essential tool for aerodynamic development, there are regions within the flight envelope where RANS methods reach their limits. In these regions massive separations due to high pressure gradients or shocks occur. The presentation covers the simulation at these limits using DES-methods to simulate low and high speed stall on extruded airfoils. At first, an overview over the new implementations in the unstructured DLR-TAU-Code is given. Numerical results for a backward facing step are compared to experimental results and provide a validation basis for further examined cases. Especially differences in the results of DES and RANS methods are highlighted and a way to determine the percentage of turbulence kinetic energy is shown. Because DES is very sensitive to the spatial discretization in the LES domain, different methods to estimate it are presented. These methods include the use of priori made URANS simulations to directly calculate the length scale, to determine the limits of the inertial subrange of the energy spectra or to create the model energy spectra suggested by Pope. Finally, two airfoils at stall conditions using DES implementations in the DLR-TAU code are presented. First, the separation on a NACA0012 airfoil at high angle of attack is simulated. Second, the OAT15A profile is examined at high speed stall conditions showing shock induced separation with a fast moving shock on the upper side of the airfoil.