Reaction Regimes in Supersonic Combustion

Abstract

Large-eddy simulations (LES) of supersonic combustion are considered to be an important tool to better understand the physics of supersonic reactive flows. To correctly predict the flame anchoring and the flame structure, the implementation of a appropriate SGS scale model is crucial, and its physics and derivation are analyzed in the present work. In fact, when modelling mixing and combustion at small scales, all effects of compressibility must be accounted before attempting to reproduce experimental results and predict performance. The theoretical analysis in [1], shows that at high Mach, high Re numbers, mixing and combustion are driven not only by transfer of kinetic energy by vortex stretching, as in subsonic reacting flows, but also by compressibility and baroclinic effects: this affects the classical -5/3 Kolmogorov scaling for the energy transfer from large to small scales. Further, compressibility favours combustion by increasing reaction rates. The increase of the reaction rate leads to an increase of flame speed: as a consequence, reaction regimes at Ma > 1(in particular those where some form of premixing occurs) must be re-examined. In fact, depending on the reaction rate, Mach and turbulence intensity, different regimes are possible that are analyzed. Based on these, an appropriate turbulence-chemistry coupling model must follow. Such model (dubbed ISCM) has been derived and implemented in a CFD LES code to simulate SCRJ combustion. Results show good agreement with experimental data.