Numerical Study of Effect of Inflow Velocity Fluctuation on Flame Structure in Unsteady Counterflow Premixed Flame

The flame structure of unsteady two-dimensional counterflow premixed flame is investigated by numerical simulation with elementary reaction mechanism. In order to investigate unsteady behavior sinusoidal fluctuations are added to the inlet velocity as follows : u0=um {1+A·cos (2πky) ·sin (2πft)}. We consider two types of counterflow ; one is methane-air premixed mixture/air counterflow, and the other is methane-air premixed mixture/burnt gas counterflow. The flame structure and the unsteady behavior in each type of counterflow are investigated under the condition of very high intensity of fluctuation (the average velocity : um=1.0 m/s, the amplitude : A=5). It is shown that the local quenching, the unburned island and the burnt island are generated. These phenomena are examined by the distributions of chemical species and heat release rate near flame surface. Moreover, it is shown that the turbulent burning velocity, which is evaluated based on 02 mass consumption rate, is directly proportionate to the flame surface area, and the time variation of the spatial averaging burning velocity per unit flame surface area is small compared with that of the flame surface area.