Particle bed deformation in front of a weir induced by subcritical laminar flow

Abstract

The behaviour of a particle bed subjected to viscous flow upstream of a weir is experimentally examined. Experiments were conducted in a rectangular flume in which oil circulated above a bed of solid particles. Within about 150 mm upstream of the weir, the bed underwent a significant change and took the shape of a dune. The temporal evolutions of dune position and dune size were determined for various discharges and weir heights. At the steady state, both parameters were independent of discharge but affected by the weir height. Results indicate that the position of the axial dune crest varies linearly with the weir height. The two mechanisms controlling the formation and evolution of the dune are the particle bed loading by the approach flow and the particle entrainment inside the separation boundary layer.

Keywords:

• Bed-load
• gravity settler
• open channel flow
• particle bed deformation
• particle entrainment
• weir

Acknowledgements

The authors would like to thank TOTAL Ltd for providing the research grant of the present study. Mrs Susan Baker is gratefully acknowledged for proof reading.