LES-based Eulerian PDF approach for the simulation of scramjet combustors

A probability density function (PDF) approach to account for turbulence–chemistry interaction in the context of large eddy simulation (LES) based simulation of scramjets is developed. To solve the high-dimensional joint-composition PDF transport equation robustly, the semi-discrete quadrature method of moments (SeQMOM) is employed. The SeQMOM approach addresses key numerical issues in LES related to the inaccuracies in computing filter-scale gradients, enabling an efficient and numerically consistent solution of the PDF transport equation. The computational tool is used to simulate a cavity-stabilized Mach 2.2 supersonic combustor. The LES–SeQMOM approach captures the pressure profiles qualitatively, in spite of the large uncertainties in the boundary conditions. Further, this flow configuration is found to exhibit low-frequency dynamics that lead to oscillatory motions of the shock-system inside the combustor. Detailed analyses of the LES data are used to describe the physical mechanism leading to these oscillations.