A Numerical Study of Flame Instability and Cell Dynamics of Opposed Nonpremixed Tubular Flames near Radiation-Induced Extinction Limit

The flame instability and cell dynamics of opposed nonpremixed tubular flames near radiation-induced extinction limit are investigated using high fidelity numerical simulations with various initial conditions (IC). When the radiation effect is considered, two different extinction Damköhler numbers (i.e. large radiation-induced extinction Damköhler number, DaE,R, and high stretch-induced extinction Damköhler number, DaE,S) are obtained by 1-D analysis with different radiative intensity, I. Two critical Das, DaC,C and DaC,O, near DaE,R are identified by the linear stability analysis. In 2-D simulations using the perturbed IC, it is found that near DaE,R, the flame instability is categorized into four different regimes with different instability characteristics. When the radiation effect is extremely large, decaying or growing oscillatory instability appears although the stretch rate is high enough, and the cellular instability occurs in the whole Da at which the flame can survive