Study of CFD variation on transport configurations from the second drag-prediction workshop

This paper describes and analyzes a series of nearly 90 CFD test cases performed as a contribution to the second Drag Prediction Workshop, held in Orlando, Florida in June 2003. Two configurations are included: DLR-F6 wing-body and wing-body-nacelle-pylon. The ability of CFD to predict the drag, lift, and pitching moment from experiment--including the “delta” arising from the addition of the nacelle and pylon--is assessed. In general, at a fixed angle of attack CFD overpredicts lift, but predicts the ΔCL reasonably well. At low lift levels (CL < 0.3), ΔCD is 20-30 drag counts (30-45%) high. At the target lift coefficient of CL  =  0.5, ΔCD is overpredicted by between 11 and 16 counts. However, the primary contribution of this paper is not so much the assessment of CFD against experiment, but rather a detailed assessment and analysis of CFD variation. The series of test cases are designed to determine the sensitivity/variability of CFD to a variety of factors, including grid, turbulence model, transition, code, and viscous model. Using medium-level grids (6-11 million points) at the target lift coefficient, the maximum variation in drag due to different grids is 5-11 drag counts, due to code is 5-10 counts, due to turbulence model is 7-15 counts, due to transition is 10-11 counts, and due to viscous model is 4-5 counts. Other specific variations are described in the paper.