Mass and heat transport barriers of opposing jet on leading edge of blunt body and thermal protection mechanism

Combined with numerical simulation and Lagrangian coherent structures （LCSs）， the mass and heat transport barriers of opposing jet on the leading edge of blunt body were studied in order to reveal the thermal protection mechanism of opposing jet on the leading edge of supersonic vehicle. First， the SST k-ω turbulence model was used to simulate the flow field of the blunt body with opposing jet flow under freestream Mach number is 3.98 and pressure ratio of 0.4， 0.6， and 0.8， respectively. Next， based on an analysis of the flow field characteristics， the effects of different pressure ratios were explored. Finally， the LCSs analysis method was introduced to identify the mass and heat transport barriers in the reverse jet flow field from the Lagrangian viewpoint. The results showed that， with increasing pressure ratio， the opposing jet pushed the bow shock further upstream and expanded the coverage area of the vortex region， enhancing the heat reduction effect. A mass transport barrier always exists between the freestream flow and the cooling jet， preventing direct contact between the hyperthermal gas and the blunt body surface. Further， the jet shear layer dominates the formation and evolution of the heat transport barrier. Due to the inhibition of heat transport by the jet shear layer， a heat transport barrier is formed between the jet-freestream shear layer and jet-vortex shear layer. However， the disappearance of the jet-freestream shear layer and the reattachment of the jet-vortex shear layer could also lead to the termination of the heat transport barrier. The findings capture the mass and heat transport characteristics in the opposing jet， providing new viewpoint on the thermal protection mechanism of opposing jet.