Velocity Measurements in a Rectangular Embayment Attached to a Straight Open Channel

Abstract

わんど内の流れおよびわんど・主流部間の交換を検討するための基礎的実験として, 長方形凸部を有する直線開水路流れにおいて速度計測を行った.その結果, 凸部の開口幅を大きくすることにより交換が促進されること, 水深の条件によって交換機構が全く異なることが明らかにされた他, 凸部が連続した場合には個々の凸部形状が合同であっても交換現象は同一ではなく, 単一の凸部における現象が代表値とはなり得ないことが示唆された.

Velocity measurements were carried out in a straight open channel with a rectangular embayment. Two laser Doppler anemometers (LDA) and an electromagnetic current meter (EMC) were employed. Flow exchange between the main flow region and the dead zone, formed within the embayment, is investigated. Turbulent shear region induced at around the junction between the main flow and the dead zone is also studied.Rough sketch of the flow structure drawn from preliminary experiments indicates that large circulating flow is induced in the embayment for the inbank case, however such a circulation cannot be seen for the overbank case. In this case flow exchange between the embayment and its adjacent flood plain takes place in a quite complex manner. Aspect ratio of the embayment also affects the exchange process. For the tested cases arectangular embayment, whose aspect ratio is 3, exchanges more effectively than the square embayment case due to instability of the dominant circulating flow formed in the embayment.