Investigation of Mean Spanwise Asymmetry in a Symmetric 3D Supersonic Cavity

Supersonic cavity flows contain many complex flow features, including shear layer instabilities, recirculation, and resonance phenomena due to pressure oscillations. The details depend on the cavity geometry and the flow conditions, and may induce noise, structural damage, and aerodynamic instability of stores. The flowfield becomes more complex at supersonic speeds, where shock waves arise and interact with the shear layer. A particularly interesting aspect in finite-width configurations that are symmetric about a mid-plane, as in aircraft-bays, is the emergence of possible asymmetric states. In this work, large-eddy simulations (LES) are employed to investigate the three-dimensional mechanisms that give rise to such asymmetric flow behavior. The results indicate that the shear layer emanating from the leading-edge lip bifurcates beyond the mid-domain, leading to asymmetric flow characteristics downstream. In the specific mean realization obtained in the present work, the shear layer thickens more on the left side (looking downstream) of the symmetry plane relative to the right. Impingement of the asymmetric shear layer on the back wall generates compression waves and large-scale asymmetric vortical structures due to the Kelvin-Helmholtz (K-H) instability. Additionally, a tornado-like vortex forms originating near the cavity floor, with its axis primarily in the vertical direction, and sustained by the primary recirculation flow. Sound pressure level (SPL) calculations indicate that the asymmetry has minimal effect on the Rossiter modes along the centerline of the cavity. A reduction in cavity length (at constant depth and width) results in the upstream migration of the tornado vortex, accompanied by the emergence of additional sidewall-bounded and corner vortices. Conversely, increasing the cavity width (while maintaining a constant length and depth) leads to the bifurcation of the tornado vortex into two counter-rotating structures. In the absence of sidewalls, these vortices dissipate, and the flow exhibits spanwise symmetry.