Effects of fuel Lewis number on wall heat transfer during oblique flame-wall interaction of premixed flames within turbulent boundary layers

Abstract

Abstract The influence of fuel Lewis number LeF on the statistical behaviour of wall heat flux and flame quenching distance have been analysed using Direct Numerical Simulation (DNS) data for the turbulent V-shaped flame-wall interaction in a channel flow configuration corresponding to a friction velocity-based Reynolds number of 110 for fuel Lewis number, LeF, ranging from 0.6 to 1.4. It has been found that the maximum wall heat flux magnitude in turbulent V-shaped flame-wall interaction increases with decreasing LeF but just the opposite trend was observed for 2D laminar V-shaped flame-wall interaction and 1D laminar head-on quenching cases. This behaviour has been explained in terms of the correlation of temperature and fuel reaction rate magnitude with local flame surface curvature for turbulent flames due to the thermo-diffusive effects induced by the non-unity Lewis number. The wall heat flux magnitude and wall shear stress magnitude are found to be negatively correlated for all cases considered here. Moreover, their mean variations in the streamwise direction are qualitatively different irrespective of LeF, although the magnitudes of wall heat flux and wall shear stress increase with decreasing LeF. Furthermore, the flame alignment relative to the wall also affects the wall heat flux and it has been found that local occurrences of head-on quenching can lead to higher magnitudes of wall heat flux magnitude. It has been found that LeF also affects the evolution of the flame quenching distance in the streamwise direction with the progress of flame quenching for different flame normal orientations with respect to the wall. This analysis shows that the effects of fuel Lewis number on flame orientation, correlations of reaction rate and temperature with local flame curvature and coherent flow structures within turbulent boundary layer ultimately affect the wall heat transfer and flame quenching distance. Thus, the thermo-diffusive effects arising from the non-unity Lewis number need to be taken into account for accurate modelling of wall heat transfer during flame-wall interaction in turbulent boundary layers.