Coherent Structures' Dynamics and Its Role to Entrainment in Turbulent Forced Plume

1)测量了湍流平面射流和湍流羽流的平均和湍流特性，特别是雷诺数剪应力和湍流热通量。结果表明，与射流相比，浮力增加了羽流中的湍流水平。例如，在羽流中，最大雷诺剪切应力高出近60%。发现恒定涡流粘度模型适用于描述两种流动中的湍流结构。此外，还分析了两种流动之间湍流动能平衡的差异。湍流能量的浮力产生大约是羽流中剪切能量产生的30%。2)利用流动显示技术和速度波动和温度波动两点测量技术，对平面强迫羽流中相干结构的动力学特性进行了实验研究。整体平均以温度锋的出现为条件。平均结果表明，大尺度相干结构在中心线两侧交替出现，它们是由相互相反环流的涡卷组成的。排出流体的扑动可能是由于结构的不对称排列造成的。从拓扑的角度来看，环境流体的夹带是通过沿着收敛的分离矩阵向连接相邻的、每侧相同设计的涡状结构的鞍点的吞没进行的。3)对湍流平面射流和羽流中相干结构的涡街模型进行了数值模拟。重点讨论了实验检测到的相干结构的拓扑特征。模型公式中包含了von karman型涡旋街型的相似尺度关系。结果表明，该模型能够较好地预测包括雷诺应力在内的平均流动和湍流量的横向分布，特别是射流和羽流中它们的量的差异。相干结构的非对称排列是产生雷诺应力和夹带的重要机制。少

1) The mean and turbulent properties, notably the Reynolds shear stress and turbulent heat fluxes of turbulent plane jets and plumes are measured. The results show that buoyancy increases the turbulence levels in plumes when compared with jets. For example, the maximum Reynolds shear stress is nearly 60 % higher in plumes. The constant eddy viscosity model is found to be applicable to describe the turbulence structure in both flows. Furthermore, the differences in turbulent kinetic energy balance between both flows are examined. The buoyant production of turbulent energy is about 30 % of the shear production in plumes.2) Coherent structures' dynamics in plane forced plumes is investigated experimentally by using a flow visualization and two-points measurement of velocity fluctuations and temperature fluctuations. Ensemble averages are conditioned on the occurrence of temperature fronts. The averages show that large scale coherent structures appear alternately on both sides of the cente … More rline, which consist of vortex roll of opposite circulation each other. A flapping motion of discharged fluid is likely attributed to the asymmetric arrangement of the structures. From topological consideration, entrainment of ambient fluid proceeds by engulfment along the converging separatrix towards the saddle point connecting adjacent, samesigned vortical structures on each side.3) A numerical simulation of the vortex-street model for the coherent structures in a turbulent plane jet and plume is described. Attention is focussed on the topological features of the coherent structures detected experimentally. The model formulation includes the streamwise development of von karman-type vortex street pattern in terms of the similarity-scaling relationships. The model was found to predict the lateral profiles of mean flow and turbulence quantities including the Reynolds stress, in particular, the differences of their quantities in a jet and a plume reasonably well. The non-symmetric arrangement of coherent structures is the essential mechanism for the production of the Reynolds stress and the entrainment. Less