Local extinction and reignition in a turbulent lifted flame

Abstract

Direct numerical simulation (DNS) was used to analyse local extinction and reignition in a lifted turbulent flame. The edge flame propagation velocity appears to be dependent on the scalar dissipation rate consistent with previous experimental and numerical studies. This dependency is analysed with a model proposed for laminar triple flames, showing a good agreement for moderate scalar dissipation rates and an under- and over-predictions of the DNS results in very low and high scalar dissipation rates, respectively. These discrepancies are then explained based on the model’s assumptions. The extinction and reignition are also analysed separately where the distinction is made based on the average hole diameter. It is revealed that during the extinction process, the edge flame is primarily a nonpremixed flame and propagation velocity reduces in a non-linear manner as scalar dissipation rate increases. In the reignition process, the flame experiences a wide range of premixed and non-premixed modes and the edge propagation velocity, conditionally averaged on the scalar dissipation rate decreases linearly when the scalar dissipation rate increases.