Structure and Dynamics of Turbulent Elementary Vortices

在对基本涡的基本性质的研究中，定量地阐明了基本涡的物理特性的空间分布和雷诺数依赖性，表明基本涡在较大雷诺数下仍能保持其动力学重要性。本文提出了一种涡的自动追踪方法，用来寻找涡的反平行逼近，它使流线和流面在时间上呈指数拉伸。流体的可压缩性已被证明可以诱导涡波并抑制涡的增长。在MHD湍流中发现了对流涡与磁场相互作用的发电机现象。在Couette湍流中发现了伴随基本涡的产生和破裂的不稳定周期运动。在对基本涡的基本动力学性质的研究中，我们研究了有无轴向流存在下，大尺度相干垂直结构与湍流场的相互作用。在前一种情况下，产生细尺度涡并缠绕在涡面上，在拟序涡内部产生轴对称弯曲涡。另一方面，在后者中，由基元涡产生的涡环增强了涡核周围的能量耗散。在Poiffille湍流中，与内层一样，在外层也观察到纵向涡和条纹结构。

In the study of the basic properties of the elementary vortices, the spatial distribution and the Reynolds number dependence of their physical characteristics have been clarified quantitatively, suggesting that the elementary vortices may keep their dynamical importance at larger Reynolds numbers. An automatic chasing scheme of vortices has been developed to find the anti-parallel approach of vortices, which stretch the fluia lines and surfaces exponentially in time. The compressibility of fluids has been shown to induce vortex waves and to suppress the vortex growth. A new dynamo phenomenon by interactions between convection vortices and magnetic fields has been discovered in MHD turbulence. unstable periodic motions accompanying the generation and breakdown of the elementary vortices has been found in Couette turbulence. In the study of basic dynamical properties of the elementary vortices, the interaction of large-scale coherent vertical structures and turbulent field has been investigated with or without the axial flow in the coherent vortices. In the former case, fine scale vortices are generated and wrapped around the vortex surface, and axi-symmetric bending vortices are generated inside the coherent vortex. In the latter, on the other hand, vortex rings produced from the elementary vortices enhance the energy dissipation at the periphery of the vortex core. In a Poiseuille turbulence, longitudinal Vortex and streak structures have been observed in the outer layer like as in the inner layer.