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The nonlinear response of inverted 'V' flames to equivalence ratio nonuniformities

机译：倒“ V”火焰对当量比不均匀性的非线性响应

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摘要

Recent studies indicate that heat release fluctuations generated by equivalence ratio perturbations may constitute sources of instability with effects similar to those induced by acoustic perturbations. The present article addresses this issue by considering the dynamics of an inverted laminar dihedral ("V") flame spreading in an open geometry when this flame is submitted to equivalence ratio modulations. The problem is investigated with numerical simulations by first establishing a steady state flame which then evolves in a uniform flow transporting a fixed level of equivalence ratio perturbations. The flame features wrinkles of increasing amplitude locking on the converted composition perturbations. The wrinkling amplitude grows with distance from the injector. For sufficiently large wrinkle amplitudes, the flame interacts with the fresh mixture outer boundary, giving rise to sudden disruptions of the flame sheet. The rapid burning of fresh mixture pockets generates a nonlinear heat release signal with abrupt changes in the waveform. It is found that high levels of modulation induce axial velocity perturbations, which in turn interact with the flame and modify the response. Calculations described in this article may serve to guide analytical modeling of the response of combustion to equivalence ratio inhomogeneities. A simple model is devised on this basis to distinguish regimes corresponding to weak and strong interactions.
机译：最近的研究表明，当量比扰动产生的热释放波动可能构成不稳定源，其影响类似于声扰动引起的。本文通过考虑当火焰经受当量比调制时以开放几何形状传播的倒层流二面体（“ V”）火焰的动力学来解决此问题。首先通过建立稳态火焰，然后以均匀流的形式发展，并输送固定水平的当量比扰动，来通过数值模拟研究该问题。火焰具有皱纹，皱纹的振幅增加，锁定在转换后的成分扰动上。起皱幅度随距喷射器的距离而增加。对于足够大的皱纹幅度，火焰与新鲜混合物的外边界相互作用，从而引起火焰片的突然破坏。新鲜混合物袋的快速燃烧会产生非线性的放热信号，其波形会发生突变。已经发现，高水平的调制会引起轴向速度扰动，而轴向扰动又与火焰相互作用并改变响应。本文中描述的计算可用于指导燃烧对当量比不均匀性响应的分析建模。在此基础上设计了一个简单的模型来区分对应于弱交​​互和强交互的机制。

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