Type I to type II transition in swept-forward fin shock interactions

The transition from type I to II in the swept-forward fin–shock interaction is studied both numerically and analytically. The transition conditions are numerically obtained using an inviscid computational fluid dynamics method. The results are compared with the classical three-shock theory, in which the detachment criteria are computed based on the parameters immediately after the shock. A discrepancy is observed, where the critical swept-forward angles from the numerical results are always larger, with a maximum deviation of 5°. Detailed flow patterns indicate this deviation is caused by the downstream of the bow shock wave. By analyzing the shock patterns in a wide range of both the inclined shock angles and the swept-forward angles, three mechanisms are identified. The first mechanism is related to the Mach reflection formed by a transmitted shock reflecting on the wall. When the top of the Mach stem reaches the fin–shock interacting point, the interaction transits from type I to II. The second is associated with a secondary transmitted shock wave achieving its maximum deflection angle. The last is due to the subsonic channel linking the symmetric and lateral planes. The quantities of the advanced transition are derived theoretically and in good agreement with the numerical results. The results have potential to benefit the aerodynamics and aerothermodynamics design of hypersonic vehicles.