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• Four cavities of different depths were evaluated to determine the cavity induced transition after the cavity. • The shallowest cavity is a "closed" cavity, inducing the widest transition, caused by the strong adverse pressure gradient and horseshoe vortex instability. • The other three deeper cavities are all "open" cavities. • Medium depth cavity did not induce transition. • The two deepest cavities induced a narrower transition, caused by shear layer instability. Cavity-induced transition (CIT) in a hypersonic boundary layer was simulated by employing direct numerical simulation (DNS). The upwind Roe scheme was discretized by high-order minimum dispersion and controllable dissipation (MDCD) reconstruction based on high-quality multi-block structured grids. The grid scale and time step are determined after evaluating the grid scale and nondimensional time step and comparing with the available measurements. Four depths, 1.0, 1.5, 2.0, and 2.5, multiplied by the baseline depth (D), are evaluated to determine their effects on the CIT on the wall after the cavity. The baseline is a typically "closed" cavity and the width of turbulent region at one cavity length downstream cavity (x = 2 L) is 67 mm, caused by the strong adverse pressure gradient and horseshoe vortex instability. Typically, the other three are "open" cavities with no transition for the 1.5 D cavity, a turbulent region width of 26 mm for the 2.0 D cavity, and 45 mm for the 2.5 D cavity at x = 2 L were obtained after the cavity. Moreover, the relationship between the flow structures and a typical high heat flux region is explored. Reattachment supplies heat to the wall, and separation removes heat from the wall. [ABSTRACT FROM AUTHOR]

Hypersonic flow transition from laminar to turbulent due to the surface irregularities, like local cavities, can greatly affect the surface heating and skin friction. In this work, the hypersonic flows over a three-dimensional rectangular cavity with length-to-width-to-depth ratio, L : W : D , of 19.9:3.57:1 at two angles of attack (AoA) were numerically studied with Improved-Delayed-Detached-Eddy Simulation (IDDES) method to highlight the mechanism of transition triggered by the cavity. The present approach was firstly applied to the transonic flow over M219 rectangular cavity. The results, including the fluctuating pressure and frequency, agreed with experiment well. In the hypersonic case at Mach number about 9.6 the cavity is seen as “open” at AoA of −10° but “closed” at AoA of −15° unconventional to the two-dimensional cavity case where the flow always exhibits closed cavity feature when the length-to-depth ratio L / D is larger than 14. For the open cavity flow, the shear layer is basically steady and the flow maintains laminar. For the closed cavity case, the external flow goes into the cavity and impinges on the bottom floor. High intensity streamwise vortices, impingement shock and exit shock are observed causing breakdown of these vortices triggering rapid flow transition. [ABSTRACT FROM AUTHOR]