Filtered mass density function for variable-density turbulent reactive flows on unstructured meshes

The scalar filtered mass density function (SFMDF) methodology, which has been shown to be an effective method for Large Eddy Simulation (LES) of turbulent reacting flows, has been implemented in a hybrid fashion in an unstructured, parallel, finite volume (FV) fluid dynamic solver. Hybrid, in this context, means that the hydrodynamic variables (total density, velocity and pressure) are calculated using the Eulerian finite volume code, while the species mass fraction and the total static enthalpy are obtained by solving the modelled transport equation for the SFMDF using a Lagrangian Monte Carlo scheme. The main advantage of the SFMDF formulation is that the chemical source term appears in a closed form and does not need to be modelled. In this work a parallel Lagrangian Monte Carlo solver has been developed and coupled with a high-order, unstructured Finite Volume solver (US3 D) developed at the University of Minnesota. The ability to run on parallel architectures and on unstructured grids enable the use of the SFMDF approach to tackle problems of considerable size and geometric complexity. Simulations carried out on three-dimensional mixing layers show that the results of LES-SFMDF hybrid method are consistent with those obtained by the conventional LES (LES-FV). When chemical reactions are considered the superiority of the LES-SFMDF over LES-FV is demonstrated by comparing the results obtained by the two methodologies against the results of a Direct Numerical Simulation (DNS) of a two-dimensional temporal developing mixing layer. The LES-SFMDF results yield a closer agreement with the DNS results.