2023 Fiscal Year Final Research Report
Effects of model scale on characteristics of void fraction and velocity in hydraulic jumps
| Project/Area Number |
19K04624
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 22040:Hydroengineering-related
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| Research Institution | Nihon University |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2024-03-31
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| Keywords | 跳水 / 射流 / エネルギー減勢 / 空気混入率 / 流速特性 |
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| Outline of Final Research Achievements |
Effects of Froude number on velocity characteristics and water surface fluctuations are shown for a given Reynolds number. It is illustrated that water surface begins to fluctuate slightly upstream of the critical point. The water-surface fluctuations and turbulence intensities downstream of the critical point are obtained, demonstrating the length required for the water-surface fluctuations and turbulence intensities to fully develop.
For a given Reynolds number and Froude number, velocity characteristics in hydraulic jumps are investigated under both undeveloped and fully developed inflow conditions, showing the effects of boundary layer development on velocity characteristics in hydraulic jumps. For undeveloped inflow conditions, the experimental investigations reveal characteristics of velocity and air-concentration in hydraulic jumps, clarifying the effect of Reynolds number on hydraulic characteristics in hydraulic jumps.
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| Free Research Field |
水工水理学
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| Academic Significance and Societal Importance of the Research Achievements |
開水路流現象の多くは，原型での水理現象にフルード相似則を適用して水理模型実験で再現し，実験結果に基づいて水工設計する手法が用いられている．しかし，模型縮尺を小さくしすぎると粘性の影響が大きくなってしまい，原型と異なる流れになることが知られている．跳水を対象とする場合については，本研究課題成果によって，レイノルズ数の大きさが30000から60000よりも大きくなると，空気混入率と流速特性に対するレイノルズ数の効果は認められないことが示された．この成果によって，水理模型実験を行う場合，レイノルズ数の大きさが30000よりも小さい場合は，河川や水路などで生じる原型の現象を再現できないことが示された．
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