Characteristics of a subgrid model for turbulent premixed flames

Abstract

A modified version of the linear eddy model (LEM) for subgrid combustion is developed and used for studying the properties of turbulent premixed flames in the core region of Couette flow. The handling of the burning (diffusion/reaction) and specie transport, in this new approach, is fully deterministic. The model is, therefore, found to predict the correct laminar flame speed in the limit of zero turbulence. The effect of three dimensional eddies on scalar fields at the subgrid scales is modeled using a stochastic Lagrangian rearrangement procedure. The derivation of this procedure from the inertial range scaling laws necessitates a calibration procedure since the numerical values of the constants in these laws are unknown. The present LEM approach relates the constant needed to the coefficient of eddy viscosity that is evaluated in a LES, under the assumption of constant turbulent Prandtl and Schmidt numbers. The new approach is found to predict the turbulent flame speed with fair amount of accuracy. The chemistry is modeled using a self propagating scalar field (G-equation) approach and within the limitations of this model, LEM is found to capture the right trends in evolution of flame structure, effects of heat release and turbulence. The encouraging results obtained here warrant further research into extending this subgrid model for cases of finite rate chemistry and inclusion of thermodiffusive mechanisms such as the Lewis number effects.

Subgrid modeling of unsteady two-phase turbulent flows

“…The two-phase LES model has been successfully implemented into a 3D zero-Mach number code developed earlier for gas phase combustion (Menon and Chakravarthy, 1996;Chakravarthy and Menon, 1997). Briefly, this code solves the gas phase LES equations on a nonstaggered grid using a high-order finite difference scheme.…”

“…The capabilities of this model have been demonstrated in the above noted studies by carrying out quantitative comparison with high-Re experimental data obtained in reacting shear layers. Application of this method to premixed combustion has also been recently demonstrated (Menon et al, 1993b;Smith, Menon and Chakravarthy, 1996;Chakravarthy and Menon, 1997. Results show that this method can capture thin, highRe turbulent flames without any numerical dissipation. The predicted turbulent flame speed was also shown to be in reasonable agreement with high-Re data.…”

“…No fundamental problems in extending the subgrid two-phase model to compressible flows are expected. Zero-Mach number approach involves using a series expansion in terms of Mach number to remove the acoustic component from the compressible Navier-Stokes equations and is a well established method (McMurtry et al, 1989;Chakravarthy and Menon, 1997). A key feature of this expansion is that the pressure field is split into two parts: a kinematic pressure (p) related to the velocity field and a thermodynamic pressure (p) that must be specified.…”

Recent Advances in DNS and LES. Proceedings of the Second AFOSR International Conference on DNS and LES Held at Rutgers - The State University of New Jersey, New Brunswick, New Jersey on June 7-9, 1999

“…Here, a subgrid version of the linear eddy mixing (LEM) model (Kerstein, 1989;Menon et ah, 1993;) is used to model the effects of unresolved turbulence on the flame structure. This approach has been used in the past to model three dimensional (3D) flame kernels (Chakravarthy and Menon, 1997) and flames in twodimensional stagnating turbulence . The present study focuses on flames stabilized by the axial strain rate in stagnating flows and swirl flows.…”

Parallel simulations of reacting two-phase flows - A DoD Grand Challenge progress report

“…The two-phase subgrid model was first implemented into a 3D zero-Mach number code developed earlier (Chakravarthy and Menon, 1997). Briefly, this code solves the LES equations on a nonstaggered grid.…”