Results from the 3rd Drag Prediction Workshop Using the NSU3D Unstructured Mesh Solver

Abstract

Results from the third AIAA Drag Prediction Workshop using the unstructured mesh Reynolds averaged Navier-Stokes (RANS) solver NSU3D are presented. Computations include a grid convergence study on a transonic wing-body and wing-body-fairing configuration at a fixed CL condition using grids up to 41 million points, as well as an incidence sweep (drag polar) at fixed Mach and Reynolds number. A second set of results on a pair of closely related wing geometries is also described, including a grid convergence study at fixed incidence, and an incidence sweep (drag polar) for both wing geometries. For all cases, approximate second-order accurate grid convergence characteristics are demonstrated, with overall accuracy and eciency comparable to other structured, overset, and unstructured workshop calculations. However, it is found that diering grid converged results may be inferred based on dierent families of self-similar coarse and fine grid sequences, particularly for values such as absolute drag at fixed incidence. More consistent grid convergence for idealized drag values (omitting induced drag) is observed, thus validating the procedure of performing grid convergence studies at fixed CL. These grid convergence issues are attributed to the large range of disparate scales which must be resolved in aerodynamic flows, and point to the need for further advances in quantifying and resolving discretization errors for such problems. Over the last five years, the AIAA Applied Aerodynamics Committee has sponsored three Drag Prediction Workshops (DPW), with the aim of assessing the state-of-the-art of current Computational Fluid Dynamics (CFD) solvers at predicting absolute and incremental drag changes on generic transonic transport aircraft configurations.