Richard Mathews @Richard-Mathews-4

Article Numerical simulation of the turbulent flow around a complex ...

For the complex pier, the scour hole appears to have gradients less than the angle of repose of the sediment and so an accurate shape can be measured during experiments by slowing the flow and draining the water. For a single cylinder, the bed shear due to each vortex will allow a sediment angle that is more or less steep than the angle of repose, depending on direction of circulation. Any slopes steeper than the angle of repose will collapse when the water flow is stopped, concealing this detail and so possibly giving an incorect shape for numerical modelling. It may be worth investigating the effect of scour holes with such a shape to see if the vortex pattern remains the same. In a similar way the use of a planar lid on the flow ignores the presence of the surface roller, thus making the numerical model representative of a deeper flow with a stagnation plane at the level of the lid. This may affect the flow in the wake vortex, since the free surface cannot drop around the pier in the manner observed in flume experiments. Is it possible to model a lid with a profile that follows the expected free surface profile, to examine the effect of pressures in the wake vortex, since these must impart enough energy to lift entrained sediment above original bed level to enable scour to progress.