Three-dimensional numerical model for open-channels with free-surface variations

A numerical model to calculate three-dimensional turbulent flow in open cha nnels of arbitrary cross-section is developed and validated. The model solv es the incompressible, Reynolds-averaged Navier-Stokes (RANS) equations, fo rmulated in generalized curvilinear coordinates, in conjunction with the ka ppa-epsilon turbulence closure. The free-surface elevation is determined by allowing the computational mesh to deform during the iterative solution pr ocedure so that the proper kinematic and dynamic conditions are satisfied a t convergence. The numerical model is validated by application to simulate the flow through meandering open channels for which detailed experimental m easurements are available. Comparisons of the computed solutions with exper imental data reveal that the model predicts the details of the velocity fie ld, including changes in secondary motion, the distribution of bed shear, a nd variations of flow depth in both the transverse and longitudinal directi ons.