Experimental and numerical investigation of local scour around a submerged vertical circular cylinder in steady currents

Local scour around a submerged vertical circular cylinder in steady currents was studied both experimentally and numerically. The physical experiments were conducted for two different cylinder diameters with a range of cylinder height-to-diameter ratios. Transient scour depth at the stagnation point (upstream edge) of the cylinder was measured using the so-called conductivity scour probes. Three-dimensional (3D) seabed topography around each model cylinder was measured using a laser profiler. The effect of the height-to diameter ratio on the scour depth was investigated. The experimental results show that the scour depth at the stagnation point is independent on cylinder height-to-diameter ratio when the later is smaller than 2. The increase rate of equilibrium scour depth with cylinder height increases with an increase in Shields parameter. A three-dimensional finite element numerical model is developed for simulating local scour around submerged vertical cylinders. Steady flow around the cylinder is simulated by solving the Reynolds- Averaged Navier–Stokes (RANS) equations with a k–ω turbulence closure. Both suspended load and bed load sediment transport rates were included in the model. Efforts are made to reduce the computational time associated with three-dimensional morphological modelling including the use of wall-function to avoid resolving the near-wall boundary layers, large morphological time step and parallel computing techniques. Scour around a submerged vertical circular cylinder founded on the seabed is simulated and the numerical results are validated against the test data. The scour mechanisms around the submerged cylinder are investigated using the numerical model.