Author(s): Feng Cai; Akihiro Tominaga; Sayed Hashmat Sadat
Linked Author(s): Akihiro Tominaga
Keywords: Submerged; Flow structure; Bed deformation; Scour; PIV; L-shape; Groyne
Abstract: A box groyne is composed of various types of single groyne to satisfy the different river ecological requirements. In order to create an appropriate watery and sedimentary environment for aquatic life in the groyne zone during flooding, the investigation of the three-dimensional flow structure and the sediment transport around the box groyne under the submerged condition is necessary. The flow velocity around submerged box groynes with an upstream longitudinal block, which is composed by straight and L-shape groyne, are measured by PIV (Particle Image Velocimetry) on the horizontal plane (x-y) and vertical plane (x-z) in the fixed bed. The dynamical interaction effects between the vertical vortex detached from the crest of the first groyne and the transverse vortex detached from the lateral side of the first groyne dominate the flow structure in the groyne zone. Under these two effects, the three-dimensional flow pattern in the inner zone is varied significantly among the box groynes with different block lengths. The measurement of bed deformation is also conducted in a movable bed flume under clear water condition. When the length of longitudinal block becomes longer, the maximum scour depth and region of scour hole around the tip of the first groyne is decreased. The sediment transport between the inner zone and the main channel is greatly reduced by the arrangement of longitudinal block. The position and scale of deposition in the inner zone are significantly changed by the complex flow with different block lengths. When the longitudinal block is set, a scour hole in front of the second groyne appears as that in front of the first groyne. In the main stream, the existence of the upstream longitudinal block enhances water in the upper level beyond the box groyne transported to the low level of the main stream, causing a scour hole in the downstream of the main channel. The flow structure obtained by the experiment of fixed bed is helping to investigate the formation mechanism of the bed deformation.
Year: 2013