Modelling of the Tangential Strain Rate Term in the Flame Surface Density Transport Equation in the Context of Reynolds Averaged Navier Stokes Simulations: A Direct Numerical Simulation Analysis

Mohit Katragadda,Sean P Malkeson,Nilanjan Chakraborty

doi:10.1155/2014/927408

Mohit Katragadda, Sean P Malkeson + Show 1 more

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https://doi.org/10.1155/2014/927408

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Abstract

A direct numerical simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different values of Karlovitz number Ka, turbulent Reynolds numberRet, heat release parameterτ, and global Lewis number Le has been used to assess the models of the tangential strain rate term in the generalised flame surface density (FSD) transport equation in the context of Reynolds averaged Navier Stokes (RANS) simulations. The tangential strain rate term has been split into contributions arising due to dilatation rateTDand flame normal strain rate (-TN). Subsequently,TDand (-TN) were split into their resolved (i.e.,TD1and (-TN1)) and unresolved (TD2and (-TN2)) components. Detailed physical explanations have been provided for the observed behaviours of the components of the tangential strain rate term. This analysis gave way to the modelling of the unresolved dilatation rate and flame normal strain rate contributions. Models have been identified forTD2and (-TN2) for RANS simulations, which are shown to perform satisfactorily in all cases considered, accounting for the variations in Ka,Ret,τand Le. The performance of the newly proposed models for the FSD strain rate term have been found to be either comparable to or better than the existing models.

Highlights

Flame surface density (FSD) based reaction rate closure is one of the most well-established methods of turbulent premixed combustion modelling in the context of Reynolds averaged Navier Stokes (RANS) simulations [1,2,3,4,5,6,7,8,9,10,11,12]
The flame surface area generation/destruction due to fluid straining plays a key role in the FSD transport and the statistical analysis and detailed assessments of the modelling of the tangential strain rate term in the FSD transport equation in the context of RANS simulations have been considered in the current work because the strain rate term remains a leading order contributor to the FSD transport [3,4,5,6,7,8,9,10,11,12]
The effects of Lewis number Le, turbulent Reynolds number Ret, Damkohler number Da, Karlovitz number Ka, and heat release parameter τ on the statistical behaviour and RANS modelling of the tangential strain rate term in the FSD transport equation are yet to be addressed in detail and the present paper aims to address this gap in the existing literature

Summary

Introduction

Flame surface density (FSD) based reaction rate closure is one of the most well-established methods of turbulent premixed combustion modelling in the context of Reynolds averaged Navier Stokes (RANS) simulations [1,2,3,4,5,6,7,8,9,10,11,12]. The flame surface area generation/destruction due to fluid straining plays a key role in the FSD transport and the statistical analysis and detailed assessments of the modelling of the tangential strain rate term in the FSD transport equation in the context of RANS simulations have been considered in the current work because the strain rate term remains a leading order contributor to the FSD transport [3,4,5,6,7,8,9,10,11,12]

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