Crossflow-Induced Transition Prediction Using Coupled Navier-Stokes and e(N) Method Computations

Abstract

The flow around two infinite swept wings and an infinite swept cylinder model is computed using a Reynolds averaged Navier-Stokes method coupled to a boundary-layer and transition prediction method based on the e(N) approach. The configurations were wind-tunnel tested, including transition location measurements. In all test cases, transition is provoked purely by crossflow instabilities. The infinite swept wing experiments represent critical test cases because they contradict two assumptions made in the conventional e(N) approach, where the limiting cross-flow N factor is supposed to be independent of the surface curvature and the quality of the wing surface finish. It will be shown that the extended version of the e(N)- method can resolve this problem and produce acceptable results. The infinite swept cylinder model tested at high sweep angles between 53 and 71 deg is excellently suited to demonstrate that the e(N)-method is capable of describing the leading-edge contamination problem. For sweep angles between 53 and 58 deg, a relative constant limiting crossflow N factor exists, whereas for higher sweep angles the crossflow N factors at the measured transition location decrease gradually. Applying the leading-edge contamination criterion of Pfenninger, the e(N)-method predicts the sweep angle, where leading-edge contamination starts to influence the laminar boundary-layer flow. Furthermore, the sweep angle, which produces, according to an empirical correlation, fully turbulent leading-edge flows, is well predicted by the e(N)-method.