1986 Fiscal Year Final Research Report Summary
Coherent Eddies in a Compound Channel and Their Effects on Flow Resistance
| Project/Area Number |
60460159
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | University of Tokyo |
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Principal Investigator |
TAMAI Nobuyuki Professor,Department of Civil Engineering, Univ. of Tokyo, 工学部, 教授 (90010818)
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| Co-Investigator(Kenkyū-buntansha) |
KAWAHARA Yoshihisa Research Associate,Division of Construction Eng.,Tech. Univ.of Nagaoka, 工学部, 助手 (70143823)
HIROSAWA Yusuke Assistant, Dept. of Civil Eng., Univ. of Tokyo, 工学部, 助手 (40010813)
ASAEDA Takashi Associate Professor, Dept.of Civil Eng., Univ. of Tokyo, 工学部, 助教授 (40134332)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Compound Channel / Coherent Eddies / Interaction between Main Channel and Flood Plain / Additional Shear Stress / Turbulence Model / Upwelling / せん断層不安定 |
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| Research Abstract |
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.
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Research Products
(14 results)
