A nested grid based computational fluid dynamics model to predict bridge pier scour Available to Purchase

A three-dimensional numerical model that computes hydrodynamics and morphodynamics is applied to the problem of calculating local scour around cylinders. A nested grid approach is implemented in the numerical scheme in order to decrease the overall computational demand but at the same time allow for high spatial resolution around the cylinder to increase numerical accuracy there. The computational grid consists of two structured blocks – a coarse block that discretises the entire domain and a fine block that only discretises the area around the cylinders. A novel interpolation technique accomplishes communication between the two blocks. Sediment transport in the morphodynamic model is calculated with a bed load transport formula combined with the sediment continuity equation to reproduce the unsteady scour hole development while the flow field is recalculated at each time step. Experimental data of flow and the local clear-water scour around single and multiple circular cylinders in a laboratory channel with a movable bed are obtained and compared with the results of the model. Flow, the maximum scour hole depth and the general scour hole geometry are reproduced well in all cases. The time evolution of the scouring is also captured reasonably well.