The Reduction Effect of Air Entrainment on the Scour Capacity by Plunging Jets
Project/Area Number |
63550380
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Research Category |
Grant-in-Aid for General Scientific Research (C)
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Allocation Type | Single-year Grants |
Research Field |
Hydraulic engineering
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Research Institution | Nishinippon Institute of Technology |
Principal Investigator |
AKASHI Nobuyoshi Nishinippon Institute of Technology, Faculty of Engineering, Associate Professor, 工学部, 助教授 (50098951)
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Project Period (FY) |
1988 – 1989
|
Project Status |
Completed (Fiscal Year 1989)
|
Budget Amount *help |
¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1988: ¥700,000 (Direct Cost: ¥700,000)
|
Keywords | Scour / River Bed Degradation / Air-Entraned Jet / Impinging Jet / Jet / Free overfall / Abrupt Drop / Energy Dissipater |
Research Abstract |
The purpose of this research is to make clear the reduction effect of air entrainment on the scour capacity by plunging jets from nappes falling over abrupt drop. The characteristics of the deflected jet along the fixed horizontal bed and the scour capacity were investigated. In the experiments, the some small spoilers behind the drop were set for enlargement of air-entrained discharge. The deflected jet is divided into two regions. In the first region, the velocity increases by the contractiori of the flow caused by impingement. In the second region, the velocity decreases by the diffusion of flow. The velocity scale and the pressure scale on the bed are prescribed by the length of the first region. The characteristics of the deflected jets were connected with air-entrained discharge. It was shown by the calculation based on the momentum equation of boundary layer that the bed shear stress becomes small when the air-entrained discharge increases. The scouring process is divided into three stages; progressive, interium, and last stage. In the progressive and interium stages, sands are transported in the form of the tractive notion, and in the last stage, in the form of the suspended motion. The progress of scour were calculated by using the equation of the river bed degradation based on non-equilibrium sediment transportation. The Scour models introduced into the calculation are the model of flow along the scouring surface, the balance model of forces acting on the slope of scour hole, the collapse model of the slope of scour hole from the sway of jet, the model of suspended sediment transportation by the deflected jet out of the scour hole, and so on. It was shown that the scour capacity decreases when the air-entrained discharge increases.
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Report
(3 results)
Research Products
(16 results)