Inlet Mach number ratio and static temperature ratio coupling effect on vortex structure characteristics downstream of the flameholder in subsonic-supersonic mixing flow

The effect of the inlet Mach number ratio and the static temperature ratio between the supersonic and the subsonic flows on the distortion characteristics of the recirculation zone downstream of the flameholder was experimentally investigated. The fluid structure was visualized and measured by a calibrated particle image velocimetry system under the subsonic-supersonic mixing flow, which was constructed by a flat plate to divide the rectangular flow channel. The present results reveal that the fluid structure downstream of the flameholder remains stable over a wide range of the inlet Mach number ratio and exhibits insensitivity to changes in the inlet static temperature ratio. Increasing the inlet Mach number ratio enhances the distribution area and the mixing effect of the subsonic-supersonic shear layer, resulting in an amplified asymmetry of the dual-vortex and a larger vortex size near the supersonic mainstream. The static temperature ratio influences the ejection effect of the supersonic flow on the subsonic flow, causing the recirculation zone to shift toward the supersonic mainstream and facilitating interaction with the subsonic-supersonic mixing layer. The findings contribute to a better understanding of the interaction between the subsonic-supersonic shear layer and the recirculation zone, offering guidance for improved subsonic-supersonic mixing flow designs in combustion systems.