Coherent Eddies in a Compound Channel and Their Effects on Flow Resistance

复合通道中的相干涡流及其对流动阻力的影响

• 批准号: 60460159
• 负责人: TAMAI Nobuyuki
• 金额: $ 4.67万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1985
• 资助国家: 日本
• 起止时间: 1985 至 1986
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-60460159/
• 关键词: Compound Channel; Coherent Eddies; Interaction between Main Channel and Flood Plain; Additional Shear Stress; Turbulence Model; Upwelling; せん断層不安定

The role and origin of large coherent eddies generated at the interface between the main channel and the flood plain in compound channels are clarified in this study through theoretical analysis, experiments, and mathematical simulations.The generation mechanism of coherent eddies in compound channels was investigated by a series of comparative experiments and a hydrodynamic stability theory for shear layers. Experimental results confirmed that coherent eddies were not produced without velocity difference between neighboring shear layers. Furthermore, it was found out that secondary upwelling along a vertical wall was unable to produce coherent eddies on the water surface. The wave number of the most unstable disturbance at the interface of two shear layers obtained theoretically agrees well with observed wave number of coherent eddies in compound channels.The intensity of upwelling which exists near the interface was estimated by a simple model where the gradient of vortity was determined by a stretching of vortex tube due to the main flow. Predicted values were in good agreement with measured values by a flow visualization technique.Depth-averaged velocity field was theoretically solved. Additional shear stress which exerted on the interface was derived theoretically and confirmed to be in good agreement with existing experimental results for a wide range of width to depth ratio of the channel. Utilizing the theoretical solution, bulk hydraulic parameters, for instance, representative roughness coefficient and energy coefficient which are required for a one-dimensional analysis were determined.A turbulence model was developed using the algebraic stress model. Isovels of the primary flow abd secondary flow, the intensity of secondary flow, and distribution of tubulence energy were reproduced pretty well compared with measured results. Computed results also made the estimation possible for the magnitude of each term in turbulence energy balance.

本文通过理论分析、试验和数值模拟，阐明了复式河槽主槽与滩地交界面相干大涡的作用和成因，并通过一系列对比试验和剪切层水动力稳定性理论，探讨了复式河槽相干大涡的产生机理。实验结果证实，在相邻剪切层之间没有速度差的情况下，不可能产生相干涡。此外，它被发现，次级上升流沿着一个垂直的墙壁是无法产生的相干涡的水面上。理论计算得到的两剪切层界面处最不稳定扰动波数与观测到的复合通道相干涡波数吻合较好，用一个简单的模型估算了界面附近的上升流强度，其中涡度梯度由主流引起的涡管拉伸决定。计算结果与流场显示测量结果吻合较好，并从理论上求解了深度平均速度场。在宽深比范围内，理论推导出了作用在界面上的附加剪应力，与已有的实验结果吻合较好。利用理论解确定了一维分析所需的代表性糙率系数和能量系数等水力参数，并采用代数应力模型建立了紊流模型。计算结果较好地再现了一次流和二次流的等值线、二次流强度和湍流能量分布。计算结果也使湍流能量平衡中各项大小的估计成为可能。

项目成果

Tamai, N. , Asaeda, T. and Ikeda, H.: "Generation mechanism and periodicity of large surface eddies in a compound channel flow" Proc. of 5th Congress, Asian and Pacific Regional Div. , IAHR. 2. 61-74 (1986)

Tamai, N.、Asaeda, T. 和 Ikeda, H.：“复合通道流中大表面涡流的生成机制和周期性”Proc。

Tamai,N.;Asaeda,T.;Ikeda,H.: Proc.5th Congress.Asian and Pacific Regional Div,Int.Assoc.for Hydraulic Research. 2. 61-74 (1986)

Tamai,N.；Asaeda,T.；Ikeda,H.：第五届国会水利研究国际协会亚洲及太平洋地区分部。

Tamai, N., Asaeda, T. and Ikeda, H.: "Structure of coherent eddies at the interface of a compound channel (in Japanese)" Proc. of Annual Meeting, Japan Soc. of Civil Engineers. 41. 313-314 (1986)

Tamai, N.、Asaeda, T. 和 Ikeda, H.：“复合通道界面处的相干涡流结构（日语）”Proc。

河原能久,玉井信行: 水理講演会論文集. 31. 425-430 (1987)

Yoshihisa Kawahara，Nobuyuki Tamai：液压会议记录 31. 425-430 (1987)。

Kawahara, Y. and Tamai, N.: "A study on the resistance law of flow in compound prismatic channels (in Japanese)" Bulletin of Technological University of Nagaoka. 8. 233-242 (1986)

Kawahara, Y. 和 Tamai, N.：“复合棱柱形通道中流动阻力规律的研究（日语）”长冈工业大学通报。