Abstract:
Drag reduction is important for improving the performance of scramjet engines operating at high Mach numbers. One demonstrated method for reducing skin friction drag on a surface exposed to hypersonic flow is the injection and combustion of hydrogen fuel in the boundary layer. This paper reviews the research progresses of skin friction reduction by boundary layer combustion from three aspects including experiments, theory analyses, and numerical simulations. The experiments have demonstrated their effectiveness and analyzed different influencing factors. The ability of applying this drag reduction technique to real hypersonic flight vehicles is primarily established. The theoretical prediction model for skin friction and heat flux of the boundary layer flow where the combustion occurs has been proposed and its accuracy was demonstrated by comparing with experiments and numerical studies. The numerical simulations have helped researchers to understand the mechanism of skin friction reduction by boundary layer combustion deeply. For the research progresses of this technique, University of Queensland in Australia is at the leading level of the world. Europe, America, Russia and Japan seem having little interest on this field and very few technical papers can be found publicly from these countries. While Chinese researchers has made some progresses but still need to do lots of work, epspcially in the experimental field, to catch up with the world leading level.