The Flame Surface Speed Budget for Turbulent Premixed Flame Stabilization Studies

摘要

Mathematical expressions linking the flame, the flow and the flame surface speeds are derived and discussed in this article. A theoretical decomposition of the flow variables is first introduced and used throughout the article. This decomposition leads to static and dynamic flow components. The static component is a non-oscillating field (also called base flow) while the dynamic component is a fluctuating field, due to turbulence, broadband noise, harmonic modulation, vortical wave. The G-equation which models the propagation of a flame front into a flowfield is then used along with the kinematic expression linking the flame speed, flow velocity and flame surface velocity vectors. Those expressions are the starting point to derive relationships between these quantities for multiple configurations of practical interest such as turbulent and modulated flames. The terms of those relationships are discussed and lead to the determination of the propagation mode for turbulent flames. The phenomena such as blowout and flashback are discussed with the perspectives brought by those obtained expressions. In addition, the case of a modulated turbulent swirling flame brings an exact expression for the ratio of fluctuating displacement burning velocity to its static value which is compared to a previous literature expression. Numerical simulations are conducted to support the theoretical development and to determine the stabilization mechanisms of swirling flames. It is suggested that for the near injector region, the flame is stabilized by a competing mechanism where both static flow and dynamic components (due to turbulence and acoustics) are important while the remaining location of the flame is dominantly stabilized by the dynamic component. In addition, the perspectives of splitting the flame speed into its static and dynamic components are discussed with respect to flame stabilization, turbulent combustion and flame dynamics.