Receptivity and Stability of Supersonic Swept Flows

The receptivity, stability, and transition of three-dimensional supersonic boundary layers over 1) a swept cylinder, 2) a swept wing with a sharp leading edge, and 3) a swept wing with a blunt leading edge are numerically investigated for a freestream Mach number of 3. These computations are performed for the same conditions as those in the experimental and computational study of Archambaud et al. (Archambaud, J. P., Louis, F., Seraudie, A., Arnal, and Carrier, G., "Natural Transition in Supersonic Flows: Flat Plate, Swept Cylinder, Swept Wing," AIAA Paper 2004-2245, 2004). The steady flowfields with and without roughness elements are obtained by solving the full Navier-Stokes. equations. The N factors computed in this study at the transition onset locations reported by Archambaud et al. for flows over the swept cylinder are approximately 16.5 for traveling crossflow disturbances and 9 for stationary disturbances. The N factors for the traveling crossflow are high based on past experiences. However, they are comparatively smaller than those reported by Archambaud et al., who found N-factor values in the range of 20 to 25 for traveling disturbances and 13 to 20 for stationary disturbances. The N factors computed for the traveling and stationary disturbances for the flow over the sharp wing are approximately 7 and 2.5, respectively, and for the flow over the blunt wing are 6.5 and 4.8, respectively. The initial amplitudes of the stationary crossflow vortices originating from the isolated roughness elements for the flow over the cylinder are about 300 times smaller than those generated in flows over the sharp and blunt wings with the same roughness heights. This explains the large differences observed in the N factors at the transition onsets between the flow over the cylinder and the wings.