Large eddy simulation of turbulent variable density and reacting flows

This thesis describes the development of a large eddy simulation code for low-Mach number variable density non-reacting and reacting flows. Governing equations for large eddy simulation of variable density flows have been derived based on low-Mach number approximation. Mixture fraction conserved scalar method has been adopted for variable density non-reacting flows and turbulent non-premixed combustion flows, with a subgrid PDF method for turbulence-mixing and turbulence-chemistry interactions. Reaction progress variable method with an algebraic flame surface density model has been used for turbulent premixed combustion flows. Explicit numerical solution procedure has been developed, with modified convective outflow boundary condition to ensure global mass conservation and feedback method to generate fully developed turbulent inflow field. For turbulent reacting flows with large density ratio, relaxation method has been adopted to remove unphysical. high-frequency fluctuations and to maintain numerical stability. The code has been validated against a number of experimental test cases, including: non-reacting variable density confined jets over a large range of non-isothermal Craya-Curtet number and initial density ratio; turbulent non-premixed combustion in a simplified axisymmetric combustor geometry; and turbulent premixed combustion in the ORACLES dump combustor. The good results obtained in these simulations have demonstrated the robustness and accuracy of the large eddy simulation code developed in present study.