Physics and Regimes of Supersonic Combustion

摘要

Understanding the physics of supersonic combustion is the key to design a performing engine for scramjet-npowered vehicles. Despite studies on supersonic combustion dating back to the 1950s, there are still numerousnuncertainties and misunderstandings on this topic. The following questions need to be answered: How doesncompressibility affectmixing, flame anchoring, and combustion efficiency?How longmust a combustor be to ensurencomplete mixing and combustion while avoiding prohibitive performance losses? How can reacting turbulent andncompressible flows be modeled? Experimental results in the past have shown that supersonic combustion ofnhydrogen and air is feasible and takes place in a reasonable distance, which is a necessary requirement in actualnhypersonic vehicles powered by supersonic combustion ramjets. These results are explained based on a theoreticalnanalysis of the physicalmechanisms driving mixing and combustion in supersonic airstreams, where they are foundnto be different from those in the incompressible regime. In particular, the classic Kolmogorov scaling is shown to benno longer strictly valid, and the flame regime is predicted to be significantly affected by compressibility and differentnfrom that of subsonic flames. This analysis is also supported by the results of the numerical simulations presented,nshowing that by generating sufficiently intense turbulence, a supersonic combustion flame is short and can indeednanchor within a small distance from fuel injectors, with the flame typically burning in the so-called flamelets-in-neddies regime.