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Flow Structure Around Two Rows of Cylindrical Rods in Vegetated Floodplain of a Compound Channel

Author(s): Alireza Keshavarzi; James Ball

Linked Author(s): James Ball

Keywords: Main channel/floodplain boundary; Vegetation; Compound channel; PIV

Abstract: In this paper, an experimental study is presented to understand the effect of trees on the structure of turbulent flow in a vegetated flood plain. To simulate trees in vegetated bank, two rows of vertical rods were attached on the floodplain. Two-dimensional velocity fluctuation around the rods was measured using PIV. The coherent turbulent flow structure or bursting events and associated shear stresses play an important role in sediment entrainment and bed instability in an open channel. The bursting analysis is used to find the turbulent flow structure at different cross section behind the rods. For the experimental test, the contribution probability of bursting events to the Reynolds shear stress was computed at different points of the flow depth. It was found that the probability of outward inteaction and sweep events is higher than ejection and inward interaction events at 60 mm depth level above the bed. Also, the distribution of ejection event was found uniform in flow field over the flood plain. The probability of outward interaction is high at area close to the edge of flood plain, however, the probability of sweep event is high at the middle of flood plain and behind the piles. The turbulent kinetic energy at different points was computed from velocity fluctuations and the average turbulent energy showed a significant variation from upstream to downstream of the piles.


Year: 2014

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