Shock-induced combustion in high-speed wedge flows

Abstract

OH planar laser-induced fluorescence (PLIF) and schlieren imaging were applied to investigate shock-induced combustion phenomena on a 40° wedge in an expansion tube. OH PLIF was utilized to determine the regions of combustion in the flow field, while schlieren imaging provided complementary shock-wave visualization. Stoichiometric H 2 /O 2 gas mixtures, at three different levels of nitrogen dilution (75, 80, and 85%), were tested at two different test-flow conditions in these experiments. A pressure transducer was mounted in the wedge to obtain a record of the surface-pressure history on the model. Three test cases yielded shock-induced combustion behind an attached shock at the tip of the wedge. Depending on the sensitivity of the mixture employed, the flame front either rapidly converged with the shock or slowly diverged away from it. The measured wave angles and surface pressures in these tests were, in general, well modeled by shock-polar theory using frozen thermochemistry. Two other test cases, using the most sensitive gas mixtures, produced a closely coupled flame front behind a detached shock wave near the wedge tip. The measured surface pressure in this latter case was better modeled by a shock polar using equilibrium chemistry. Simple finite-rate chemistry modeling of the ignition zone agrees well with the experimental results in all cases.