A study on flow past a suspended bluff object in an open channel

Abstract

Detailed velocity and erosion measurements in the near wake of a flat plate with a gap between the plate and the channel bed in an open channel are presented. A "wall jet" like flow (confined to the wall region) is observed to interact with the wake flow behind the body. Two axial stations downstream of the body were chosen to obtain the velocity profiles in the near wake region. The span-wise velocity profiles across the wake at two distances from the channel bottom were also obtained. This yielded information in the development of the "wall jet" like flow and also provided some sense of the velocity components in the near wake. At mid-section of the gap, the streamwise mean velocity attains its peak value at one body width. The velocity measurements across the wake exhibit the cause of erosion. Erosion measurements were simulated on an erodible sand bed of D50 = 0.59 mm grain size. The erosion patterns obtained show symmetry about the centerline of the plate. A ripple-like pattern was observed with deeper scour holes generated towards the edge of the wake. Flow separations from the lower corners and the sides of the plate account for this typical nature of the erosion pattern.Key words: velocity profile, local scour, wake flow, wall jet flow.