Computation of prescribed spin for a rectangular wing and for the F-15E using detached-eddy simulation

Detached-Eddy Simulation (DES) is used to predict the massively separated flow around a rectangular wing and around the F-15E statically, and then with prescribed spinning motions. The spinning motion of the rectangular wing is driven by the autorotative rolling moment of a wing just beyond stall, while that of the F-15E is triggered by a yawing moment, itself produced by asymmetric vortex shedding from the forebody even without spin. A drag polar for the static rectangular wing is produced using both RANS and DES. The two agree for attached flow; RANS then is more accurate near maximum lift, but DES is again more accurate post stall. Strip theory is applied to the drag polars to predict the limits of autorotative instability. The RANS polar shows only a weak susceptibility to autorotation over too small of an angle-of-attack range, while the DES polar closely matches the ranges based on experimental values. A prescribed rotary motion is then calculated with DES and shows a pro-spin rolling moment, consistent with strip theory. In a parallel effort, a prescribed spin of the F-15E at 65° anglsof-attack is calculated by RANS and DES. Predictions are assessed via comparison to Boeing's stability and control database. A previous grid-resolution study leads to a 6.5 × 10⁶ cell grid of the full aircraft with an efficient distribution of points. Although the grid is coarser than the baseline grid of the previous study, accurate force predictions are retained. A small bump is added to the nose of the aircraft that triggers the asymmetric vortex shedding on the forebody, as observed in flight and wind tunnel tests at this angle of attack. The yawing moment produced by the asymmetric vortices (RANS and DES) matches the database reasonably well. The accuracy in a prescribed spin is assessed by comparing the force coefficients with those for a static condition, with reference to the stability and control database. The effect of the rotation on lift and drag is captured adequately with RANS, but that on the yawing moment is not. DES fails so far to give the correct effect, possibly because the expected change in lift and drag is quite small (less than 5%) and obscured by statistical fluctuations in a marginal time sample. Further grid retlnement may also be required. Nevertheless, the overall force coefficients in the prescribed spin are reasonably accurate and motivate a six-degree-of-freedom calculation in the near future.