Nonlinear Flame-Flow Transfer Function Calculations: Flow Disturbance Celerity Effects

This paper describes the non-linear dynamics of premixed flames responding to harmonic velocity disturbances. It extends a prior computational study which determined the key parameters influencing the nonlinear flame characteristics. It was shown that the linear and nonlinear characteristics of the flame dynamics were controlled by the superposition of two sources of flame disturbances: those originating at the flame anchoring point due to boundary conditions and from flow non-uniformities. These disturbances do not generally propagate along the flame at the same speed. Consequently, they may either constructively or destructively superpose with each other, depending upon frequency, flame length, and the ratio of their propagation velocities. The response in the linear regime was shown to be characterized by two Strouhal numbers, namely, St2 and Stc. These two Strouhal numbers are related to the amount of time taken for a flow (Stc) and flame front (St2) disturbance to propagate the flame length, normalized by the acoustic period.