Abstract: The local scour process in the downstream of Dangka hydropower station is simulated based on Fluent dynamic mesh to predict the development and topography of local scour in the downstream of dam and sluice. The VOF water-air interface tracking method is used to deal with the complex free surface in the local scour. With transient shear stress on river bed as a crucial hydrodynamic condition for sediment’s incipient motion and transport, the volumetric transport rates per unit width of sediment on river bed in different directions are calculated, based on which the transient change of river bed elevation is obtained. Moreover, an improved formula of critical shear stressfor sediment’s incipient motion is employed to refrain from abnormal numerical values of sediment transport rate caused by bed slope gradient approaching sediment’s angle of repose. Finally, the 3-D evolutionary process of local scour is acquired by adopting the spring-based method and remeshing method. The accuracy and reliability of the mathematical model are verified by comparing the simulated depth and topography of local scour with model test values.

Key words: Dangka hydropower station, local scour, dynamic mesh, VOF, shear stress, sediment transport rate, depth and topography