Author(s): Takayuki Tanaka; Terunori Ohmoto; Kota Sawa
Linked Author(s): Terunori Ohmoto, Takayuki Tanaka
Keywords: Cavity flow; Flow resistance; Turbulent flow structure; Momentum transport; PIV
Abstract: The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous. In this paper, effects of aspect ratio of side cavity on open-channel flow with submerged permeable and impermeable side cavities were examined experimentally. The experiment in this study was conducted by using a recirculating slope varying acrylic-resin flume measuring 10 m in length, 40 cm in width and 20 cm in height. Velocity fluctuations were measured by using a particle-image-velocimetry (PIV). As a result, the resistance characteristic of the overflow cases shows a similar resistance characteristic to the non-overflow cases in both permeable and impermeable side cavities and the flow resistance significantly depended on aspect ratio of side cavity. In addition, it was revealed that the influence of cavity and vegetation zone on the permeable cavity flow is more extensive than the impermeable cavity flow by the flow field. This effect was suggested to be one of the reasons that the resistance of permeable cavity flow becomes larger as compared with impermeable cavity flow at small aspect ratio. Furthermore, by examining the turbulence characteristics and the momentum transport characteristics, the details of the turbulent flow structure at each measurement position in the water depth direction were grasped. In addition, it was clarified that momentum transport form with high three-dimensionality is achieved in the overflow condition compared to non-overflow condition.
Year: 2018