This paper presents an experimental study on the vortex formation and frequency tuning of jet diffusion flames under periodic excitations. The state-of-art laser diagnostic techniques were applied to provide temporally-resolved measurements for flame and flow structures. The results show that the fame surface deformation is synchronized with the convection of the inner vortex rings (IVRs), demonstrating the crucial role of IVRs in affecting the flame dynamics. The quantitative study on vortex formation and evolution is intended to understand two mechanisms: how the IVR forms, and how it is tuned to the forcing frequency of the perturbed fuel. The qualitative agreement between the predicted circulation growth and experimental data verifies the relevance of the classical starting vortex jet model in addressing the current problem, indicating the vortex growth is mainly dictated by the shear layer of the upstream fuel. The vortex tuning is closely related to the detachment of the main IVR, which is attributed to a secondary “razor vortex” when the shearing between the fuel jet and the coflow switches direction.

本文提出了周期性激励下射流扩散火焰涡流形成和频率调谐的实验研究。应用了最先进的激光诊断技术来提供火焰和流动结构的时间分辨测量结果。结果表明，声望表面变形与内部涡流环（IVR）的对流同步，证明了IVR在影响火焰动力学中的关键作用。关于涡流形成和演化的定量研究旨在了解两种机制：IVR的形成方式以及如何将其调整到受扰燃料的强迫频率。预测的环流增长与实验数据之间的定性一致性验证了经典的起始涡旋射流模型在解决当前问题方面的相关性，表明涡旋的增长主要由上游燃料的剪切层决定。涡旋调谐与主IVR的分离密切相关，当燃料射流和顺流之间的剪切力切换方向时，这归因于次级“剃刀涡旋”。