Three-dimensional numerical flow modeling for estimation of maximum local scour depth

Abstract

Water flow is modeled numerically in three dimensions around a circular cylinder placed vertically in a flume. The numerical model solves the Navier-Stokes equations with the k-z turbulence model. This gives the shear stress on the bed. A formula for concentration at the bed as a function of the shear stress is used. The bed concentrations are used to solve the convection-diffusion equation for the sediments. Continuity for the cells close to the bed gives the bed changes. The water flow field is solved simultaneously with the sediment calculation. The models include time-dependency with transient terms, and calculation of the free surface is also done. An adaptive grid is used, which follows the changes in bed and water surface elevations. The model gives the development of the three-dimensional scour hole around the cylinder. The resulting scour hole has a maximum depth which compares well with empirical formulas for local scour.