Coupling a 3D Model With a 2DV Model Using a Free-Surface Correction Method

This paper presents an efficient method to couple a three-dimensional hydrodynamic model with a laterally averaged, two-dimensional hydrodynamic model. The methodology presented can be used for such a case where a narrow river, with a vertically two-dimensional flow pattern, flows to a relatively larger water body that has a three-dimensional flow pattern. The coupling is facilitated with a free-surface correction (FSC) method that is unconditionally stable with respect to gravity waves, wind and bottom shear stresses, and vertical eddy viscosity terms. The coupled model solves laterally averaged (2DV) RANS equations for the narrow river portion of the simulation domain and 3D RANS equations for the larger water body. The use of the FSC method allows the 3D equations and the 2DV equations to be solved simultaneously, instead of solving them in sequence. Model test runs show that the coupled model retains the efficiency of both the 3D and 2DV models, and can be run with a Courant number larger than 10.