A thermo-chemical exploration of a two-dimensional reacting supersonic mixing layer

Abstract

The hypervelocity two-dimensional reacting supersonic mixing layer experiments of Erdos et al. with a H₂/air stream have been simulated with model free fine grid calculations on a N-S solver with full and single step chemistry. Response of the flow to fluctuations in the in-flow stream is utilized to examine chemistry fluid flow interactions. A favourable comparison of the computation with experimentally measured wall static pressure and heat transfer data along with flow picture forms the basis for further analysis. Insight into the mean flow thermal and reaction properties is provided from the examination of large scale structures in the flow in which the hydrogen stream is at 103 K flowing at 2.4 km/s (M = 3.09) and the air stream is at 2400 K flowing at 3.8 km/s (M = 3.99). The chemistry-flow interaction is dominated by large stream kinetic energy and affects the mean properties including the temperature profiles across the mixing layer. Single step chemistry, in comparison to full chemistry, is inadequate to describe ignition and early combustion processes, but seems reasonable for describing mixing and combustion downstream. Fast chemistry approximation coupled with mixture fraction based on hydrogen element seems to predict H₂ mean profiles well; but this is shown to be due to the insensitivity of Y_H2 to progress of the reaction. This approximation under-predicts Y_O2 though the general shape of the profile is maintained. Mixture fraction variable approach is shown to be inadequate for the prediction of the H2O mass fraction because of the effect of non-normal diffusion. Finite chemistry conditions are shown to prevail throughout the domain of the mixing layer. It appears that use of mixture fraction approach may be inadequate to compute high speed reacting turbulent flows.