Numerical modeling of 3D turbulent free surface flow in natural waterways

We develop a numerical model capable of simulating three-dimensional, turbulent free surface flows in natural waterways. Free surface motion is captured by coupling the two-phase level set method and the sharp-interface curvilinear immersed boundary (CURVIB) method of Kang et al. [1]. The model solves the three-dimensional, incompressible, unsteady Reynolds-averaged Navier–Stokes (RANS) and continuity equations in generalized curvilinear coordinates using a fractional step method extended to handle multiphase flows. Turbulence is modeled by a two-equation RANS model implemented in the context of the CURVIB method. The accuracy of the level set method is verified by applying it to simulate two- and three-dimensional sloshing problems, and the potential of the model for simulating real life, turbulent free surface flows is demonstrated by applying it to carry out RANS simulation of flow past rock structures in a laboratory flume and flow in a field scale meandering channel. The simulations show that the method is able to accurately predict water surface elevation over complex hydraulic structures and bathymetry, and capture the transition between subcritical and supercritical flows without any special treatment.