Author(s): Arindam Sarkar; Subhasish Dey
Keywords: Erosion; open channels; seepage; submerged jets; scour; sediment transport; hydraulics
Abstract: Experiments were conducted to investigate the effect of upward seepage on the characteristics of scour hole due to horizontal submerged jets and the resulting flow field within the scour hole. In the experiments, the submerged jets had a range of submergence factors from 3.22 to 26.5 and jet Froude numbers from 0.82 to 1.48 over beds of sediments (median sizes = 0.8 mm, 1.86mm and 3 mm) downstream of a sluice gate under different upward seepage velocities. The characteristic lengths of the scour hole determined from the equilibrium scour profiles are: The maximum equilibrium scour depth, the horizontal distance of maximum scour depth from the sluice gate, the horizontal extension of scour hole from the sluice gate, the dune height and the horizontal distance of dune crest from the sluice gate. The experimental results show that all the characteristic lengths decrease with increase in seepage velocity, as a result of jet deflection by the upward seepage velocity. Using the experimental data, the time-variation of scour depth is scaled by an exponential law, where the time scale decreases linearly with increase in the ratio of seepage velocity to issuing jet velocity. The flow field within scour hole under different upward seepage velocities was detected by the acoustic Doppler velocimeter. Vector plots of the flow field show that the decay rate of submerged jet increases with increase in seepage velocity. The vertical profiles of turbulent kinetic energy and Reynolds stress at different streamwise distances and the horizontal distributions of bed shear stress acting on the scoured beds are plotted for different (with and without) upward seepage velocities.