Flow-field Structures And Mixing Mechanisms In The Wake Of Gas Sonic Transverse Jet Into A Supersonic Crossflow

The residence time of air and injected fuel in the internal flowpath of scramjet engines is of the order of milliseconds,thus,efficient mixing of fuel with air is essential to achieve a high combustion efficiency.Transverse injection into a supersonic stream is one of the most fundamental canonical flows for supersonic propulsion community.In this paper,the jet in supersonic crossflow(JISC)is analyed,including its shock wave structures,mixing mechanism and scale effect.Relying on the supersonic static wind tunnel in our group,the flow field structure was visualized by plane laser light scattering(NPLS),particle image velocimetry(PIV)and oil flow experiments.The experiment combined with the Reynolds average(RANS)numerical simulation method reveals the formation mechanism of the herringbone recirculation zone in the jet leeward.The recirculation zone is caused by the low pressure in the jet leeward,and the collision shock makes the recirculation zone V-shaped like herringbone.The spatial structure of shock waves such as collision shock wave and reflection shock wave,barrel shock wave and Mach disk are studied,and the interaction regulation is revealed.Through the RANS simulation,the distribution of fuel mass fraction in different dynamic pressure ratios(J=2.3 and J=7.7)was compared,and the relationship between the wave structure of the jet wake region and the fuel concentration distribution and mixing mechanism was analyzed.The fuel concentration distribution in the jet leeward area is very low,where filled with the inflow air.However,there is a region where the fuel mass fraction has a high magnitude.In this paper,the jet wake is divided into four different regions according to the flow field structure and fuel concentration distribution.At the same time,the influence of boundary layer thickness on fuel blending was analyzed.The velocity field at different spatial scales was measured by PIV experiments,while the penetration at different scales was measured by NPLS experiment.The oil flow experiment can reveal the slip lines at different scales.Besides,I employed RANS simulation to analyze the fuel mass distribution.Based on the comprehensive experiments and simulation results,the similarity law of transverse jet under supersonic state is established.In the case of the same dynamic pressure ratio,the jet penetration depth satisfies the similarity rate at different geometric scales.Fuel mass fraction,mixing efficiency,and velocity distribution need to meet more conditions if they satisfy the similarity rate.