This paper presents an experimental study on dynamic response of a forced low-swirl methane/air premixed flame with external acoustic excitation over a wide range of driving frequency. Global flame response in terms of gain and phase delay between flame intensity and incoming velocity perturbation is determined. Local flame response is investigated in detail at three typical frequencies: 55 Hz, 105 Hz and 155 Hz. The effect of swirl number on the flame response is also discussed. Proper orthogonal decomposition is applied to identify the large coherent structures in the forced flame. Experimental results show flame response gain exhibits a successive of valleys and peaks which is dependent on swirl number. Time delay decreases as swirl number is increased. The low-swirl flame oscillates back and forth mainly in the axial direction at low excitation frequency and it turns into radially dominated direction at high frequency. Flame intensity fluctuation is mainly dominated by the tail of the flame at 55 Hz and 155 Hz while the flame response is controlled by a combined effect of the base and tail region at 105 Hz. Further POD analysis shows symmetric, anti-symmetric and helical modes in the flame. The most energetic modes (mode 1 and mode 2) feature a symmetric wave-like structure at low excitation frequency while it tends to be in antisymmetric modes at high frequency.

本文介绍了在很宽的驱动频率范围内，在外部声激励下，强制低涡流甲烷/空气预混火焰的动态响应的实验研究。确定在火焰强度和传入速度扰动之间的增益和相位延迟方面的全局火焰响应。在三个典型频率下详细研究了局部火焰响应：55 Hz、105 Hz 和 155 Hz。还讨论了涡流数对火焰响应的影响。应用适当的正交分解来识别受迫火焰中的大相干结构。实验结果表明，火焰响应增益表现出连续的波谷和波峰，这取决于涡流数。时间延迟随着旋流数的增加而减少。低涡流火焰在低激发频率下主要沿轴向来回振荡，在高频下转变为径向主导方向。火焰强度波动主要由 55 Hz 和 155 Hz 的火焰尾部主导，而火焰响应受 105 Hz 的基区和尾部区的综合效应控制。进一步的 POD 分析显示了火焰中的对称、反对称和螺旋模式。能量最高的模式（模式 1 和模式 2）在低激发频率下具有对称的波状结构，而在高频下往往呈反对称模式。火焰强度波动主要由 55 Hz 和 155 Hz 的火焰尾部主导，而火焰响应受 105 Hz 的基区和尾部区的综合效应控制。进一步的 POD 分析显示了火焰中的对称、反对称和螺旋模式。能量最高的模式（模式 1 和模式 2）在低激发频率下具有对称的波状结构，而在高频下往往呈反对称模式。火焰强度波动主要由 55 Hz 和 155 Hz 的火焰尾部主导，而火焰响应受 105 Hz 的基区和尾部区的综合效应控制。进一步的 POD 分析显示了火焰中的对称、反对称和螺旋模式。能量最高的模式（模式 1 和模式 2）在低激发频率下具有对称的波状结构，而在高频下往往呈反对称模式。