Structural evolution and modal property of the supersonic mixing layer downstream of a splitter plate

• The instantaneous flow fields and average flow fields of the supersonic mixing layer downstream of the splitter plate were presented, and the distinctive features of the supersonic mixing layer influenced by the splitter plate were summarized. • The dominant modes in the supersonic mixing layer downstream of the splitter plate were extracted through Dynamic Mode Decomposition (DMD) analysis, and their correlation with specific vortex structures was systematically examined. • The reconstructed flow fields were obtained, and the relationship between the energy accumulation ratio of these modes and the influence of the splitter plate were investigated. Fast mixing of fuel and air is of great importance for the improvement of rocket-based combined cycle (RBCC) engine performance. Nevertheless, most direct numerical simulations (DNS) of supersonic mixing layers are based on the flow model without the splitter plate—an essential element in actual environment. Therefore, present investigation establishes a supersonic mixing layer model incorporating a splitter plate with inflow convective Mach number ( Mc ) of 0.8 and plate thickness of 4 mm. Utilizing the self-developed high-precision DNS procedure, the evolution and dynamic behaviors of flow structures in the supersonic mixing layer downstream of the splitter plate are systematically investigated. The DNS results show that: (1) the supersonic mixing layer with a splitter plate undergoes shearing and developing stage, and ultimately develops into the self-similar stage. (2) compare with the DNS results neglecting splitter plate, it is found that the presence of splitter plate accelerates the development of mixing flow and distinctly enhances the three-dimensional (3D) flow characteristics in the supersonic mixing layer. (3) through Dynamic Mode Decomposition (DMD) method, the dominant modes and accumulate energy ratio of modes are obtained, it is shown that the energy ratios of high-order modes increase significantly, which indicates that the presence of splitter plate makes the flow structures more broken. Overall, present work provides critical insights into the vortex evolution characteristics in supersonic flow. More detailed analysis regarding the fine vortex dynamics in flow developing region are suggested for further investigation.