Turbulence combustion closure model based on the Eddy dissipation concept for large eddy simulation

Abstract

Modeling of turbulence-chemistry interaction is still a challenge. Turbulence modeling with Large Eddy Simulation (LES) has been matured enough for industrial problems. In LES eddies up to the filter width are resolved on the grid scales, but the fine structures where combustion takes place are still not resolved, which calls for combustion modeling in LES. Combustion closure in LES is achieved through a Turbulence Chemistry Interaction Model (TCIM). Most of the developed TCIM are based on the already existing RANS model. In the present study, a TCIM based on the Eddy Dissipation Concept (EDC) is proposed for large eddy simulation. The model is formulated from subgrid viscosity and filtered strain rate tensor. EDC model constants are modified to account for the partial energy cascading in LES. The other model used in this study is the steady state Flamelet model. Another issue with reacting flows is the solution of the pressure correction Poisson's equation with density time derivative term, which causes severe time constraint per iteration. Density time derivative is the most destabilizing part of the calculation when the density from equation of state is used. In the present study density is formulated from species mass fraction, which is numerically stable and computationally less expensive. LES of the H2/N2 "FlameH3" non-premixed unconfined turbulent jet flame is performed using LES-EDC and Flamelet model. The Reynolds number based on nozzle diameter and jet bulk velocity is 10,000. The chemistry used for LES-EDC model is a fastchemistry. Results of the simulations in the form of means and variances of

Experimental and Numerical Analysis of Formation and Flame Precession of Fire Whirls: A Review

“…Turbulence and local equivalence ratio are presented by the mixture fraction variance, the scalar dissipation rate, and the filtered mixture fraction. With a flamelet equation solved in the mixture fraction space, the chemical kineticity is coupled [53].…”

Exploring subgrid-scale variance models in LES of lab-scale methane fire plumes

“…The filtered RTE and divergence of the radiative flux are obtained by applying the filtering operation to Eqs. (22,23):…”

“…Due to nonlinearity of the combustion process, the filtered reaction rate is modeled by introducing model constants. However, no universal values of these constants exist [23,24]. On the other hand, only few LES of fire plumes have reported the use of mixture fraction based combustion models.…”