Flame stabilisation in a highly-lifted premixed jet flame in a hot cross flow

Abstract

We report a large-scale direct numerical simulation (DNS) of a highly-lifted premixed methane–air jet flame in a hot cross flow, relevant to axially staged gas-turbine combustion systems. The jet Reynolds number is 17,938 and the cross flow Reynolds number is 28,822. Apart from pressure, the thermochemical parameters closely match practical axially staged combustors. A premixed methane–air jet with an equivalence ratio of 0.7 is injected into a vitiated cross flow comprising combustion products from a methane–air mixture at an equivalence ratio of 0.5 and atmospheric pressure. The DNS is analysed to understand the stabilisation mechanism of the flame. The DNS reveals a lifted flame quasi-statically anchored on the leeward side. Time scale and OH budget analyses demonstrate that autoignition is the dominant stabilisation mechanism, and the leeward side anchoring is explained with reference to residence time and scalar dissipation rate. The study also shows that the interaction between the counter-rotating vortex pair and leeward ignition kernels results in a premixed flame in the jet core.