Mixing enhancement in direct numerical simulation of shock wave-mixing layer interaction for aerospace propulsion

Efficient mixing of fuel and oxidizer in combustor is a key challenge in the design of high speed propulsion systems such as scramjets. Shock wave, which is commonly present in combustor, has been identified as a promising candidate for enhancing mixing through their interaction with supersonic mixing layer. This study employs direct numerical simulation (DNS) to investigate the interaction between an oblique shock and a supersonic mixing layer, and its influence on flow dynamics and mixing efficiency. A high-order finite difference scheme is used to solve the three-dimensional compressible Navier-Stokes equations, simulating the evolution of an H₂/N₂ and O₂/N₂ mixing layer under a convective Mach number of Mc = 0.43. The analysis focuses on species transport, vorticity evolution, and turbulence statistics. Results show that the oblique shock undergoes refraction and reflection upon intersecting the mixing layer, significantly modifying the mean velocity profile—from a steep gradient to a smoother S-shaped curve. The shock-induced disturbance greatly promotes the diffusion of H₂/N₂ and O₂/N₂, resulting in accelerated mixing layer thickening. Initially large-scale vortices governed by Kelvin-Helmholtz instability break down into smaller structures under shock interaction, yielding a more diffused vorticity field and highly disordered turbulence. The shock further strengthens turbulent momentum and energy exchange via enhanced shear production, baroclinic vorticity generation, and vortex fragmentation, leading to a stepwise increase in Reynolds stresses and turbulent kinetic energy downstream. This study provides valuable insights into shock-driven mixing enhancement and offers theoretical and numerical support for optimizing mixing performance in supersonic combustors.