CFL3D/OVERFLOW Results for DLR-F6 Wing/Body and Drag Prediction Workshop Wing

Abstract

A series of overset grids was generated in response to the Third AIAA CFD Drag Prediction Workshop (DPW-III) which preceded the 25th Applied Aerodynamics Conference in June 2006. DPW-III focused on accurate drag prediction for wing/body and wing-alone configurations. The grid series built for each configuration consists of a coarse, medium, fine, and extra-fine mesh. The medium mesh is first constructed using the current state of best practices for overset grid generation. The medium mesh is then coarsened and enhanced by applying a factor of 1.5 to each (I, J, K) dimension. The resulting set of parametrically equivalent grids increase in size by a factor of roughly 3.5 from one level to the next denser level. Computational fluid dynamics simulations were performed on the overset grids using two different Reynolds-averaged Navier-Stokes flow solvers: CFL3D and OVERFLOW. The results were postprocessed using Richardson extrapolation to approximate grid-converged values of lift, drag, pitching moment, and angle of attack at the design condition. This technique appears to work well if the solution does not contain large regions of separated flow (similar to that seen in the DLR-F6 results) and appropriate grid densities are selected. The extra-fine grid data helped to establish asymptotic grid convergence for both the OVERFLOW FX2B wing/body results and the OVERFLOW DPW-W1/W2 wing-alone results. More CFL3D data are needed to establish grid convergence trends. The medium grid was used beyond the grid convergence study by running each configuration at several angles of attack so drag polars and lift/pitching moment curves could be evaluated. The alpha sweep results are used to compare data across configurations as well as across flow solvers. With the exception of the wing/body drag polar, the two codes compare well qualitatively showing consistent incremental trends and similar wing pressure comparisons.