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 innatural waterways. Free surface motion is captured by coupling the two-phase level set method and thesharp-interface curvilinear immersed boundary (CURVIB) method of Kang et al. [1]. The model solves thethree-dimensional, incompressible, unsteady Reynolds-averaged Navier-Stokes (RANS) and continuityequations in generalized curvilinear coordinates using a fractional step method extended to handle multiphaseflows. Turbulence is modeled by a two-equation RANS model implemented in the context of theCURVIB method. The accuracy of the level set method is verified by applying it to simulate two- andthree-dimensional sloshing problems, and the potential of the model for simulating real life, turbulentfree surface flows is demonstrated by applying it to carry out RANS simulation of flow past rock structuresin a laboratory flume and flow in a field scale meandering channel. The simulations show thatthe method is able to accurately predict water surface elevation over complex hydraulic structures andbathymetry, and capture the transition between subcritical and supercritical flows without any specialtreatment.