Investigation of mixing enhancement mechanisms in a cavity-based combustor with an upstream wavy wall

The cavity in a scramjet combustor plays a crucial role in stabilizing combustion, and fuel injection upstream of the cavity can enhance the mixing process within the combustor. It has been found that the installation of a periodic wavy wall in front of the injection hole can induce streamwise vortices, promoting deeper penetration of the fuel into the main flow and enabling more thorough mixing. This configuration can further expand the mixing-enhanced region and improve the overall mixing efficiency. To better understand the mechanism by which an upstream wavy wall enhances fuel mixing in cavity-type supersonic combustors, a numerical investigation using the large eddy simulation method is conducted. The study focuses on a cavity-based combustor with a wavy wall having an amplitude of 1.5 mm and a wave number of 1.5. Results show that, compared to the baseline case, the wavy wall generates oblique and reflected shocks, which increase the size of the subsonic and high-temperature regions in the combustor. This leads to enhanced flame propagation upstream and deeper penetration of the fuel jet into the main flow. The wavy wall is also capable of inducing both streamwise and spanwise vortices, thereby increasing the circulation of velocity in the vicinity of the wavy wall and in the upstream region of the cavity. In particular, the velocity circulation near the wavy wall is increased by approximately 25 m2/s. Furthermore, the analysis of pressure oscillations at the cavity floor reveals that the wavy wall enhances the size of periodically formed combustible fluid packets. As a result, combustion oscillations within the combustor are intensified.