In an experimental investigation, the stochastic dynamics of the global mode in a turbulent swirling jet are considered. From the application of the swirling jet in gas turbine combustors, it was observed that a specific density gradient in the flow leads to a suppression of the global mode. This phenomenon was replicated in a generic swirling jet using an electrical heating coil placed inside the breakdown bubble. In the present investigation, the dynamics of the global mode obtained from PIV and pressure measurements are analysed using a stochastic reduced-order model to describe the instability. The stochastic model is necessary to explain the interaction between the deterministic dynamics of the global mode and the perturbations by the background turbulence. The calibration of the stochastic model provides the amplification rate of the global mode that defines the transition of the flow, dependent on the swirling strength and the density difference. The spatial structure of the global mode is further investigated from Lagrangian coherent structures of the flow field which are computed from the 3D time-resolved velocity field reconstruction based on planar PIV measurements. The Lagrangian visualisations and schlieren visualisations are used to explain the absence of the density effects on the global mode at larger Reynolds numbers. The analysis gives a detailed view of the stochastic dynamics of a hydrodynamic instability in a turbulent flow.

在实验研究中，考虑了湍流旋流射流中全局模式的随机动力学。从涡流射流在燃气轮机燃烧器中的应用可以看出，流动中的特定密度梯度导致全局模式的抑制。这种现象在使用放置在击穿气泡内的电加热线圈的通用旋转射流中被复制。在目前的调查中，使用随机降阶模型来分析从 PIV 和压力测量获得的全局模式的动力学来描述不稳定性。随机模型对于解释全局模式的确定性动力学与背景湍流的扰动之间的相互作用是必要的。随机模型的校准提供了定义流动过渡的全局模式的放大率，取决于旋流强度和密度差异。从流场的拉格朗日相干结构进一步研究全局模式的空间结构，这些结构是根据基于平面 PIV 测量的 3D 时间分辨速度场重建计算得出的。拉格朗日可视化和纹影可视化用于解释在较大雷诺数下对全局模式没有密度影响。该分析给出了湍流中流体动力学不稳定性的随机动力学的详细视图。从流场的拉格朗日相干结构进一步研究全局模式的空间结构，这些结构是根据基于平面 PIV 测量的 3D 时间分辨速度场重建计算得出的。拉格朗日可视化和纹影可视化用于解释在较大雷诺数下对全局模式没有密度影响。该分析给出了湍流中流体动力学不稳定性的随机动力学的详细视图。从流场的拉格朗日相干结构进一步研究全局模式的空间结构，这些结构是根据基于平面 PIV 测量的 3D 时间分辨速度场重建计算得出的。拉格朗日可视化和纹影可视化用于解释在较大雷诺数下对全局模式没有密度影响。该分析给出了湍流中流体动力学不稳定性的随机动力学的详细视图。