The Employment Of Film Cooling In Scramjet And The Study Of Supersonic Film Cooling

Scramjets are considered to be the most promising propulsion for hypersonic vehicles. However, as flight Mach number is very high, the heat load is great. In order to keep the engine working safely, it is in badly need of effective active thermal protection. This paper presents a regenerative/film cooling to solve the problem that the heat sink is insufficient when regenerative cooling is used only. The paper also presents the investigation result of film cooling in supersonic freestream.The simulation method of film cooling was introduced firstly, and the method was testified by experimental data. Then the effectiveness of regenerative/film cooling was evaluated, and the effectiveness was compared with that of regenerative cooling. The results indicated that film cooling improves the effectiveness obviously, although the effectiveness is almost the same when the freestream temperature is not high. Thus there is a need to investigate the film cooling further.The film cooling in supersonic freestream was investigated without shock waves through CFD simulations. The analysis was performed following the Buckingham Theorem to reduce the parameters of influence on film cooling. Then the effect of coolant turbulence intensity, mainstream boundary layer, the gradient of mainstream and the injection angle on film cooling is simulated using CFD software. The results showed that the increasing coolant turbulence intensity reduces the film cooling effectiveness and the effect of mainstream boundary layer is complicated. The expanding of mainstream can improve the film cooling effectiveness and the influence of injection angle becomes obvious when the blowing ratio increases.The effect of shock waves and shock trains on film cooling was investigated, and the influence of shock wave strength and disposition, shock wave and expanding, and shock wave and blowing ratio was discussed. The results indicated that the effect of shock wave on different film cooling regions was not similar. The increasing shock wave strength decreases the film cooling effectiveness. The expanding of mainstream and the increase of blowing ratio can decrease the influence of shock waves.The oil gas film cooling with chemical heat sink was simulated and experimental investigated. The effectiveness was compared with that with out chemical heat sink and the influence of blowing ratio was discussed. The result indicated that on one hand the chemical reaction can improve the heat sink of film cooling and improve the film cooling effectiveness, on the other hand the increasing volume disturbs the flow, improve the turbulence intensity and decreases the film cooling effectiveness. Thus the heat sink doesn’t always improve the cooling effectiveness. The increase of blowing ratio makes the disturbance serious and the region of lower effectiveness expands.