Correlation of heat loss with quenching distance during transient flame-Wall interaction

Abstract

Detailed numerical simulations of stoichiometric premixed methane/air flames have been conducted for a side-wall-quenching (SWQ) setup, in order to study the effect of transient motion of the flame on flame-wall interaction (FWI). A W-shaped plane-jet (2D) flame is considered, which is bounded in its lateral direction by walls. The left wall oscillates in its normal direction with pre-defined frequencies f and stroke lengths L (distance between the minimum and maximum wall locations), exciting the entire flow and resulting in an unsteady motion of the flame at the left and right wall. While the instantaneous flame contours near the moving and the stationary wall differ, the instantaneous quenching distance dq and wall heat flux q˙w at the walls yield a quasi-linear correlation in the case of low f and L. However, hysteresis loops with a weakened correlation for q˙w vs. dq have been detected for large f and L, which leads to a considerably increased time-averaged dq and decreased time-mean q˙w compared with results obtained from the steady-state solution. The reason is attributed to the delayed response of the flame to the rapidly varying temperature and flow fields caused by the transient motion of the flame with respect to the wall. In this case, the flame requires a relaxation time to perceive the heat flux to the wall and to adjust its dynamics. The results indicate an essential impact of the unsteady flow nature on FWI, which has to be considered for turbulent combustion modeling. A quasi-linear correlation between the volumetric heat loss rate caused by the wall and the time-mean dq has been proposed for a first-order estimate of the effect of FWI, which could be implemented into the energy balance as sink term for modeling turbulent flame propagation under the influence of a cold wall.