Hydraulic Characteristics of Turbulent Shearing Layer at Pass-through of Artificial Block for Fish Nest

Recently, bank protection works are undertaken construction in many rivers. People try to keep rivers in a natural environment as much as possible. Under such circumstances, artificial block for fish nest comes to be cQnsidered available. To put it at bank serves as not only bank protection but also ecosystem preservation. We studied having an interest in exchanging fluid between main stream of river and inside of the block, which is one of main functions of the block. When main stream of river flow by the block, turbul.ent shearing layer becomes at pass-through of the block. Many vortexes arise in the layer. From previous reports, those vortexes cause exchanging fluid. We analyzed this system by two experiments, one is visualization for stream, another is measurement of flow velocity. The vortexes arising from the leader of pass-through move to downstream with flow. Then the size of them increases with flow. When they get to near the end of passthrough, they brush against the sidewall of channel and they are broken. At the same instant, the width of turbulent shearing layer is increasing with flow, too. ln such hydraulic phenomenon, the size of vortexes, the width of turbulent shearing layer and other turbulent quantities depend on the value of Froude number.本研究では人ロ魚巣開口部に形成される乱流剪断層の水理特性に関して，特に剥離渦の特性について，水理実験に基づき検討を行った．得られた結果をまとめると以下のようである．開口部始端で発生した剥離渦は，Fr数が大きくなるほどその渦径は大きくなり，発生周期は短くなる．また，その渦は流下とともにその渦径を増し発達する．しかし，発達した渦は開口部終端近傍で壁面への衝突により崩壊する．渦の平面形状は崩壊する直前まではほぼ円形をしている．水路側壁面近傍の流速分布については人工魚巣開口部乱流勇断層を流下する際に減衰するが，開口部終端から，次の人工魚巣の開口部始端に至るまでにほぼ回復する．また，魚巣開口部乱流剪断層ノルズ応力は流下とともに増加することがわかった