2020 年 8 巻 1 号 p. 207-220
When using a groyne for bank protection purposes, obtaining a smooth reduction of velocity from the mainstream to the bank with less turbulence around the structure is ideal. This can be achieved by applying modifications to groyne permeability or layout. Obviously, pile-arrangement type in a pile-group groyne significantly affects the downstream flow structure. However, these effects have not been sufficiently studied. In this study, the effects of different pile-group groynes on the flow characteristics were investigated experimentally. This research aimed to find an efficient design of pile arrangement in a pile-group groyne in order to produce a smooth flow reduction with low turbulence around the structure. Two types of pile arrangements, namely in-line and staggered arrays, were considered. The findings demonstrated that the staggered type caused a gradual deceleration of flow from the mainstream toward the bank, longer low-velocity field behind the structure, and drastic reduction in the turbulence around the structure when compared with the in-line type.