Analysis of the incipient motion of spherical particles in an open channel bed, using a coupled computational fluid dynamics discrete element method model

The measurement of liquid-induced erosion using CFD DEM (computational fluid dynamics discrete element method) models has been studied in detail, particularly in rough pipes. Some studies have provided measurements of the erosion rate in open liquid solid systems, but there is less information on the incipient motion of individual particles since it is difficult to design test beds that can provide reliable results. This work compares the fluid flow velocity required to initiate incipient motion of a particle predicted by a coupled CFD DEM model with measurements obtained during an experiment in an open channel under laboratory conditions. The experiment was designed to obtain a continuous flow with a slow and gradual increase in water velocity. The bed was made using two rows of spheres fixed in staggered positions, and a test sphere resting on top of the three neighbouring fixed spheres (i.e. nestling in the space between the surfaces of the fixed spheres). A 50 mm-high spillway gate was located downstream of the test sphere in order to obtain deeper water upstream, and provide more easily monitored and controllable water flows. The critical flow velocity required to initiate incipient motion in the five test spheres of different dimensions was measured by acoustic Doppler velocimetry. The difference in the results provided by the two methods was <5% (i.e. no significant difference). The coupled CFD DEM model could therefore predict this variable and could be useful for investigating incipient erosion under other conditions.(C) 2016 IAgrE. Published by Elsevier Ltd. All rights reserved.