Direct numerical simulation and analysis of the flow field around a swept laminar separation bubble

Abstract

The transition process around a short leading-edge separation bubble subjected to a sweep angle of 30° is studied in detail by means of direct numerical simulation, spatial linear stability theory and solutions of the parabolised stability equations. The combined analysis of the averaged flow field, instantaneous flow visualisations and postprocessing data as amplification curves leads to the distinction of four succeeding stages qualitatively comparable to the unswept case. It is shown that the saturation of background disturbances is the key event, after which a rapid breakdown of transitional structures occurs. The mechanism of the final breakdown of this swept scenario of fundamental resonance is best described as an "oblique K-type transition". Great care is taken to isolate and describe of typical structures within each stage as a foundation for the analysis of complex transition scenarios.