Large eddy simulation of turbulent front propagation with dynamic subgrid models

Dynamic models for large eddy simulation of the G-equation of turbulent premixed combustion are proposed and tested in forced homogeneous isotropic turbulence. The basic idea is to represent the "filtered propagation term" as "propagation of the filtered front at higher speed," where the enhanced filtered-front speed is modeled. The validity of the linear relation between the turbulent flame speed and turbulence intensity is examined through the use of filtered direct numerical simulation (DNS) data. These tests show a range of scalings from linear to cubic depending on the ratio of the turbulence intensity to flame speed as well as the filter type. Filtered DNS data are also used to evaluate the proposed dynamic model for the turbulent flame speed. It is found that the model is very sensitive to the manner in which the subgrid-scale kinetic energy is estimated. It is also found that accurate predictions of the turbulent flame speed can be obtained provided a good estimate of the subgrid-scale kinetic energy is used. Simulations are also run using the new dynamic model and the results are shown to compare well with DNS results.