Large-Eddy Simulation of Supersonic Reacting Mixing Layers

We study a class of chemically reacting, spatially evolving, supersonic mixing layers via large eddy simulation. Specifically, the goal is to reproduce the experimental results on molecular mixing and heat release performed at Caltech by Bonanos et al. Here, the mixing layer is formed as a result of the interaction of supersonic and subsonic streams: the supersonic stream expands over a 30° perforated ramp and interacts with a subsonic stream of fluid injected into the combustor through the ramp. The primary (top, supersonic) stream contains a small amount of H_2 as the fuel. The secondary stream (injected through the ramp) contains a fractional amount of F_2 which acts as the oxidizer. The hypergolic reaction between hydrogen and fluorine is characterized by a large Damköhler number, making the chemistry fast compared with the flow time scales. Hence, the product formation and temperature-rise in the flow is mixing limited. Both reacting and non-reacting simulations are performed with two turbulence models (Smagorinsky and Vreman) and the comparisons are made with the available experimental data. The reconstructed species concentrations, used in the flux evaluation, are limited using ideas from a recent paper by Zhang and Shu in order to ensure boundedness for these quantities. The simulations show close agreement of the velocity profiles and the temperature-rise profiles to those measured in the experiment