Thermal Radiation Modeling using LES-ODT Framework for Turbulent Combustion Flows

The simulation of radiation effects in a turbulent combustion flow is performed using the Monte-Carlo Ray Tracing (MCRT) technique in the Large Eddy Simulation -- One Dimensional Turbulence (LES-ODT) framework. The LES-ODT is a numerical tool used in turbulent combustion modeling. It consists of a hybrid simulation of the large scales within LES and another computational domain embedded in the LES that simulates the small scales contribution referred as ODT. In the LES-ODT framework, transport equations for mass, momentum and scalar are spatially filtered, while the effects of smaller scales are modeled [1, 80]. The large turbulence scales are flow specific and strongly dependent on the flow geometry and Reynolds number. The small scales tend to be more homogeneous and less affected by the boundary conditions [81]. LES-ODT is a promising model that situates itself between the two most common other models used in CFD: the Direct Numerical Simulation (DNS) and the Reynolds Averaged Navier-Stokes (RANS) providing a relatively close enough description of the process comparing to DNS with a significant saving in terms of CPU time and allocated memory.;Radiation is solved within the ODT domain at the subgrid scale where a combination of stochastic and deterministic solutions allows the treatment of different processes governing the transport and chemistry for scalars and momentum. The solutions are implemented in parallel on the ODT domains that are embedded in the LES computational domain.;The MCRT implementation is validated within a Direct Numerical Simulation (DNS) using a variation of the Spherical Harmonics (SH) method in a non-homogeneous auto-ignition isotropic turbulence simulation. This configuration exhibits different modes of combustion (from ignition kernels to premixed and non-premixed flames) and a complex coupling between turbulent transport and molecular processes, diffusion, reaction and radiation, under highly transient conditions.;The implementation of MCRT in the LES-ODT framework is performed for different cases of optical thickness and absorption coefficient dependency. Results of the simulations were compared to filtered density contours for the same conditions. The comparison of the different statistics shows a satisfactory agreement.