Direct numerical simulation of turbulent mixing in supersonic coflow jets

The complexity of fuel mixing in a supersonic stream within a scramjet combustor arises primarily from the inherently short residence time. Efficient fuel injection is crucial to enhance mixing and improve combustion efficiency. This study employs direct numerical simulations to explore the mixing characteristics of supersonic coflow jets at convective Mach numbers between 0.48 and 0.78. The results show that the jet mixing layer thickness increases with higher convective Mach numbers, progressing through three distinct growth phases. The highest growth rate is observed in the rapid growth region. As the convective Mach number intensifies, turbulence in the flow field becomes more pronounced, thereby enhancing mixing. At higher convective Mach numbers, stronger turbulence and a greater presence of small-scale vortex structures emerge, driving the further growth of the jet mixing layer. Dynamic mode decomposition analysis highlights that at elevated convective Mach numbers, modal energy becomes more concentrated. Additionally, high-frequency modes promote jet mixing in the fully developed region, leading to a 12.7% increase in average jet mixing layer thickness.