The presence of swirl in combustion systems produces a marked change in their boundary layer flashback behaviour. Two aspects of swirling flow are investigated in this study: the effect of the swirl-generated wall-normal pressure gradient, and the effect of misalignment between the mean flow direction and the direction of flame propagation. The analysis employs Direct Numerical Simulation (DNS) of fuel-lean premixed hydrogen-air flames in turbulent planar channel flow with friction Reynolds number of 180. The effect of swirl on the flashback process is investigated by imposing a wall-normal pressure gradient profile. Analysis of the DNS data shows how the resulting differences in flow field and flame topology contribute to the differences in the overall flashback speed. Misalignment of the flow and propagation directions leads to asymmetry in the flame shape statistics as streaks of high velocity fluid in the boundary layer cleave into the flame front at an angle, yielding an increase in flame surface density away from the wall. Swirl has a stabilising effect on the turbulent flame front during flashback along the centre-body of a swirling annular flow due to the density stratification across the flame front, and produces a reduction in turbulent consumption speed. However the swirl also sets up a hydrostatic pressure difference that drives the flame forward, and the net effect is that the flashback speed is increased. The dominance of hydrostatic effects motivates development of relatively simple modelling for the effect of swirl on flashback speed. A model accounting for the inviscid momentum balance and for confinement effects is presented which adequately describes the effect of swirl on flashback speed observed in previous experimental studies.

燃烧系统中涡流的存在会导致其边界层回火行为发生明显变化。本文研究了旋流的两个方面：旋流产生的壁面法向压力梯度的影响以及平均流向与火焰传播方向之间的不对准影响。该分析采用湍流平面通道流动中贫燃料的预混合氢-空气火焰的直接数值模拟（DNS），摩擦雷诺数为180。通过施加壁法向压力梯度分布，研究了涡流对回火过程的影响。对DNS数据的分析表明，流场和火焰拓扑结构的最终差异如何导致总体闪回速度的差异。流动方向和传播方向的不对齐会导致火焰形状统计数据不对称，因为边界层中的高速流体条纹会以一定角度进入火焰前沿，从而使远离壁的火焰表面密度增加。由于沿火焰前沿的密度分层，涡流沿回旋环形流的中心体在逆流过程中对湍流火焰前沿具有稳定作用，并降低了湍流消耗速度。但是，涡流还会产生静水压力差，从而使火焰向前推进，其最终效果是提高了回火速度。静水效应的优势促使人们开发出相对简单的模型，以模拟漩涡对闪回速度的影响。