Effects of cracking reaction on supersonic film cooling using gaseous hydrocarbon fuel as coolant

摘要

Film cooling is an effective method to thermally protect the scramjet combustors. Gaseous endothermic hydrocarbon fuel is used as coolant and parallel injected into the supersonic boundary layer to generate a cooling film, and cracking reaction is introduced during the cooling process. Effects of cracking reaction on supersonic film cooling are numerically studied using Reynolds-averaged Navier-Stokes equations. The numerical results indicate that the cooling film with cracking reaction transforms from chemical frozen flow to chemical non-equilibrium flow along the flow direction. Cracking reaction barely has any effect on the mixing process between the mainstream and the cooling film. The disturbance of cracking reaction on the film momentum is quite little. However, cracking reaction brings positive effect on supersonic film cooling through absorbing heat, which reduces wall temperature and increases film cooling effectiveness. It is found that the effects of film inlet coolant conversion, film inlet temperature and mainstream total temperature on the film cooling effectiveness without cracking reaction being considered can be ignored. However, with the cracking reaction considered, the above influencing factors all show significant effects on the supersonic film cooling but in a different way, the effect of film inlet temperature is the most significant, followed by that of mainstream total temperature, and finally that of film inlet coolant conversion which can almost be ignored.