Modeling Turbulence Mechanisms in Flows over Abrupt Drops in Bed Elevation

Results are presented of a computational study of turbulent free surface flow over an abrupt drop in bed elevation. The Reynolds averaged Navier-Stokes equations are solved using an operator splitting technique. Different constitutive laws, both linear and a nonlinear, are employed for the turbulent stress-strain relationship. A particular treatment of the troublesome Oldroyd derivative terms in the nonlinear constitutive law is advocated. The model is applied to the problem of free surface flow over an abrupt drop in bed elevation. The computational results are compared with experimental measurements. Comparisons are drawn for the mean flow field velocities, the turbulence intensities, and the Reynolds shear stresses. This technical note concludes that the use of nonlinear turbulent stress-strain relationships is an important new development in engineering fluid mechanics and advocates the future study of such constitutive laws.