Effect of sub-grid wrinkling factor modelling on the large eddy simulation of turbulent stratified combustion

Different flame efficiency function (wrinkling factor) models are compared and tested for the Cambridge stratified flame using Large Eddy Simulations (LES) with an artificially thickened flame approach. Different numerical discretisations and definitions of the outer cut-off length are tested, as different practices exist that can have a strong impact on the results. The Cambridge experiment is chosen since it exhibits a Reynolds number of more than 11,500 and the stratified flame is strongly wrinkled further downstream, making it a challenging configuration for the turbulent (stratified) combustion modelling. The sub-grid level physics have been modelled by four wrinkling factor closures, which rely explicitly on algebraic functions of resolved variables, to analyse the influence of wrinkling factor modelling on the predictions of LES. Many such models have been proposed and were tested successfully - but typically for perfectly premixed flames, using specific discretisations and definitions of the cut-off length or filter width. The present paper shows that the models tested perform well even for stratified combustion, provided that the correct definition for the cut-off length is used, and to a lesser extent, suitable discretisation methodologies are employed.