The spatial and temporal characteristics of the cavity-manipulated supersonic mixing layer with blunt base

This study explores the spatial and temporal characteristics of a supersonic mixing layer downstream of a blunt splitter plate, with particular focus on the effects of cavity excitation. Large eddy simulations combined with flow visualization and proper orthogonal decomposition (POD) reveal that embedding a cavity substantially reduces the recirculation region, advances the onset of flow instability, and accelerates the redevelopment of the mixing layer. The cavity-induced disturbances generate larger and more coherent vortical structures, leading to a 50% increase in the peak growth rate of vorticity thickness. POD analysis shows that modal energy becomes more concentrated, with dominant modes capturing nearly all the energy using fewer modes than in the baseline case. Furthermore, spectral and temporal analyses identify strict frequency-locking and periodic transitions among coherent structures, indicating a more organized energy transfer process. The cavity exhibits self-sustained oscillations with a characteristic timescale of 1.3×10−4 s, providing multi-frequency forcing that enhances mixing through amplification of linear and non-linear interactions. Overall, the results demonstrate that cavity excitation acts as an effective passive control strategy, significantly enhancing mixing efficiency and offering practical potential for rocket-based combined-cycle propulsion systems.