Numerical Simulation of Iced Swept Wing Aerodynamics with RANS, DES, and IDDES

Icing on three-dimensional lifting surfaces has been shown to produce highly three-dimensional unsteady flow fields. The objective of this chapter is to assess the ability of two Hybrid RANS-LES methods (DES and IDDES) to predict the aerodynamic performance parameters for a range of angles of attack where the flow is semi-detached. To support this objective, comparisons are made with aerodynamic results on a 65% scaled Common Research Model (CRM65) swept wing with leading-edge experimental ice shapes obtained at NASA. These ice shapes were then converted into sub-scaled 3D-printed models that were used in aerodynamic testing on an 8.9% scaled CRM65. At low angles of attack, lift, drag, and pitching moment are well predicted by RANS, DES, and IDDES. However, the numerical solutions produced by DES and IDDES for both lift and pitching moment did not fare as well at higher angles of attack where the coefficient became non-linear, e.g., the pitching moment break in the experimental data. In particular, DES and IDDES did not quantitatively capture the spanwise component of the flow over the stalled portions of the swept wing nor did they properly predict the pressure distribution along the upper surface of the wing. In contrast, a conventional RANS approach surprisingly proved superior for predicting this fluid dynamic behavior. As such, the highly complex flow over a swept iced wing at stall conditions requires further development of the DES and IDDES approaches. In particular, it is suggested that the transition between RANS and LES regions for flow separations that have high spanwise velocity components be investigated in terms of turbulent mixing in order to allow improved transition models to properly capture the three-dimensional aerodynamic behavior.