Numerical study of transverse jet mixing and combustion in a high-enthalpy supersonic crossflow with trace gases

High-enthalpy gas streams in a real engine or wind tunnel will contain some trace gases; however, this is often ignored in many studies. To investigate transverse fuel-jet mixing and combustion characteristics in a high-enthalpy inflow with trace-gas species, large-eddy simulations based on the HyShot II configuration have been adopted and verified. It was found that a trace amount of atomic oxygen (O) and nitrous oxide has a direct significance on ignition delay times and can, therefore, influence the overall flame distribution. In addition, the results show a greater sensitivity to the levels of O. The complex shock-wave system generated by the transverse jet is found to be a key factor in enhancing mixing and inducing combustion. It not only facilitates vortex generation by increasing the baroclinic term but also provides regions with high pressure and temperature, which accelerate the chemical-reaction rates for radical generation. The initial ignition locations, characterized by HO2 production rates, are mainly located in the low-speed region close to the injector, e.g., in the recirculation region, while OH is mainly formed downstream and accompanied by strong heat release. Based on the analysis of instantaneous contours and statistical results, the overall combustion was found to be in scramjet mode. The partially premixed flame dominates the combustor, where the combustion mainly lies in the flamelet regime, while the diffusion flame dominates the nozzle, where the combustion is spread over the flamelet regime, the broken flamelet regime, and the perfectly stirred reactor regime.