Assessment of Bray Moss Libby formulation for premixed flame-wall interaction within turbulent boundary layers: Influence of flow configuration

摘要

Three-dimensional direct numerical simulations (DNS) of two different flow configurations have beenperformed for premixed flames interacting with chemically inert isothermal walls at the unburned gastemperature in fully developed turbulent boundary layers. The first configuration is an oblique flame-wallinteraction (FWI) of a V-flame in a turbulent channel flow and the second configuration is a head-onquenching planar flame in a turbulent boundary layer. These simulations are representative of stoichiometricmethane-air mixture at unity Lewis number under atmospheric conditions. The turbulence in thenon-reacting conditions for these simulations is representative of the friction velocity based Reynoldsnumber of Re_τ = 110 . Differences in the statistical behaviours of the mean values of progress variable,temperature, and density during the FWI process have been reported for the two configurations. It isfound that the mean flame brush thickens in the near wall region leading to significant departures fromthe strict Bray Moss Libby (BML) formulation limit during the FWI process and that is reflected in theprobability density function (PDF) distributions of c for both flame configurations. The closures fromthe BML formulation for Reynolds averaged progress variable c and the Favre averaged variance of theprogress variable c"~2 have also been investigated and it is found that these closures need to be modifiedto account for the FWI process even when the flame away from the wall represents high Damkoehler numberpremixed turbulent combustion. Furthermore, the statistical behaviours of the quantities required forFlame Surface Density (FSD) based mean reaction rate closure including the flame orientation factor σ_y ,the flamelet length scale L_y and the flame stretch factor I_0 have been interrogated from the DNS datafor the two flame configurations. The flamelet length scale and the stretch factor extracted from the DNSdata are compared with the closures for these quantities proposed in the literature. It is found that σ_yexhibits significant spatial variation for both cases. The existing closures for L_y and I_0 which exhibit thebest quantitative agreement with DNS data have been identified. It has been found that the models for L_yand I_0 have scopes for further improvement to enable satisfactory predictions of these quantities duringthe FWI process within turbulent boundary layers.