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特性和湍流特性，特别是雷诺切应力和湍流热通量。结果表明，与射流相比，浮力增加了羽流中的湍流度。例如，羽流中的最大雷诺剪应力高出近60%。常涡粘性模型适用于描述两种流动中的湍流结构。此外，还考察了两种流动在湍动能平衡方面的差异。湍流能量的浮力产生约占垂直切变产生的30%。2)利用流动显示和速度涨落和温度涨落的两点测量，对平面强迫羽流中相干结构的动力学进行了实验研究。集合平均以温度锋的出现为条件。平均结果表明，大尺度相干结构交替出现在…中心两侧更多的涡卷，它们由相互相反循环的涡卷组成。排出的流体的拍打运动很可能归因于结构的不对称排列。从拓扑学的角度考虑，环境流体的卷吸是通过沿着收敛的分离线向连接两侧相邻的相同符号的涡结构的鞍点进行的。3)描述了湍流平面喷流和羽流中相干结构的涡街模型的数值模拟。重点研究了实验探测到的共格结构的拓扑特征。该模式包含了von Karman型涡街流型在相似尺度关系下的流向发展。结果表明，该模型能很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，特别是它们在射流和羽流中的量的差异。相干结构的非对称排列是产生雷诺应力和卷吸的重要机制。较少

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