Effects of hyperconcentrated sediment on flow resistance and structure in open channel with roughness elements

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K06583
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Hydraulic engineering
• Research Institution: Kumamoto University
• Principal Investigator: Terunori Ohmoto 熊本大学, 大学院先端科学研究部(工), 教授 (30150494)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: sediment transport / non-Newtonian fluids / open channel flow / coherent vortex / PIV

Outline of Final Research Achievements

The hyper-concentrated sediment laden flows have caused flood control, river environment and irrigation problems such as aggradation and clogging. Several researchers documented the effects of large concentrations of sediments on the fluid properties such as the viscosity, the density, and the reduction of fall velocity of bed sediment particles,the increase of sediment discharge. However, such a sediment flow feature has not been investigated in detail on the effects of suspended clay concentration on large scale vortex structure. In this paper, we experimentally investigated velocity fluctuations in hyper-concentrated sediment laden-flow in an open channel with two-dimensional square ribs by using Particle Image Velocimetry(PIV). The results showed that rheological properties significantly dissipated the large scale coherent vortex identified on the second invariant of the velocity gradient tensor over the bed with square ribs by comparison with the clear water flow.

Free Research Field

水工学

Academic Significance and Societal Importance of the Research Achievements

高濃度土砂流において粗度の影響が強いRoughness Sublayer 内の流れは，粗面乱流の抵抗則を規定する重要な領域であるにも係わらず乱れの空間変動特性について十分に検討されていない．本研究では，２次元粗度（円柱粗度，角柱粗度）3 次元粗度(球状粗度，角柱粗度)上に高濃度土砂流を発生させ，その抵抗則および高空間分解能を有し高精度の粒子画像流速計法を用いて流動機構を明らかにした。Roughness Sublayer 内の剥離渦の構造と抵抗則との関係を明らかにし，粗面乱流の普遍的構造を解明することは学術的意義が非常に大きく、河川の治水および環境機能を強化する上で基礎的知見となる