Detached eddy simulation of flow around A-airfoil

In this study the flow around the Aerospatiale A-airfoil at maximum lift (alpha = 13.3degrees) and Re = 2 x 10(6) is investigated by RANS and DES to quantify the influence of transient flow patterns on the quality of the flow prediction. This flow features a highly unsteady pressure-induced trailing-edge separation. The fairly high Reynolds number makes LES rather unattractive from a practical point of view as the numerical costs scale with approximate to Re-1.95[9] and lead to an unreasonable effort to carry out these simulations. Like LES, DES is designed to capture the unsteady flow features and consequently is supposed to give results superior to RANS. The RANS solution captures the separation, but is not able to predict transient vortex shedding. The application of DES to a 2D domain leads to results comparable to those obtained by 2D-RANS. Only the 3D-DES is capable of predicting both the unsteady flow features and the development of the boundary layer on the airfoil. As expected, the spanwise resolution has a strong impact on the vortex shedding and on the size of the separation bubble. Attention must be paid to both accommodating the full extent of the flow structures and providing the adequate spatial resolution in order to accomplish satisfactory results - that compare favourably with LES - at only a fraction of computational cost.