Improved-Delayed-Detached-Eddy Simulation of Cavity-Induced Transition in Hypersonic Boundary Layer

摘要

Hypersonic flow transition from laminar to turbulent due to the surfacernirregularities, like local cavities, can greatly affect the surface heating and skinrnfriction. In this work the hypersonic flows over a three-dimensional rectangularrncavity with length-to-width-to-depth ratio, L:W:D, of 19.9:3.57:1 at two angles ofrnattack (AoA) are numerically studied with Improved-Delayed-Detached-Eddy-rnSimulation (IDDES) method to highlight the mechanism of transition triggered byrnthe cavity. The present approach was first applied to the transonic flow over M219rnrectangular cavity. The results, including the fluctuating pressure and frequency,rnagree with experiment well. In the hypersonic case at Mach number about 9.6 therncavity is seen as “open” at AoA of -10° but “closed” at AoA of -15°rnunconventional to the two-dimensional cavity case where the flow always exhibitsrnclosed cavity feature when the length-to-depth ratio L/D is larger than 14. For thernopen cavity flow, the shear layer is basically steady and the flow maintains laminar.rnFor the closed cavity case, the external flow goes into the cavity and impinges onrnthe bottom floor. High intensity streamwise vortices, impingement shock and exitrnshock are observed causing breakdown of these vortices triggering rapid flowrntransition.