Effects of the Karlovitz number on the evolution of the flame surface density in turbulent premixed flames

摘要

Direct numerical simulation (DNS) is conducted to investigate the effects of the Karlovitz number (Ka) on displacement speed and consequent evolution of flame surface density (FSD). Parametric study is performed for the Ka between 2 and 10 in the thin reaction zone regime with independent variation of laminar flame speed and turbulent intensity. Previous study showed the effect of the turbulent intensity without noticeable influence of the Ka lower than 2.4 [I. Han, K.Y. Huh, Combust. Flame 152 (2008) 194-205]. A higher Ka involves a lower displacement speed on the positive curvature side primarily due to the influence on the normal diffusion component. It leads to a negative curvature term to act as a sink for FSD throughout a flame brush. The maximum FSD increases with increasing turbulent intensity, while a higher Ka leads to an asymmetric profile of FSD due to suppressed production at the leading edge. A higher Ka decreases total flame area and turbulent burning velocity as well, while a limiting behavior is shown for low Da cases.