Steady supercritical flow in a straight-wall open-channel contraction

Experimental and numerical modelling of steady flow in an open channel contraction is conducted. A two-dimensional depth-averaged model based on a finite volume solution of the shallow water equations is developed. A three-dimensional model of the Reynolds-averaged Navier-Stokes equations is adapted for free surface flows by incorporating the volume of fluid model. The numerical models are applied to resolve the discrepancy between earlier simulations of shallow water equation models and a benchmark dataset on supercritical open channel contraction flow. The experiment is repeated in a Plexiglas flume. Measurements are done at several flow rates. The measurements and simulations demonstrate that the original data have measurement or reporting errors, and shallow water equation models cannot reproduce observed steady supercritical flow in a straight-wall contraction. The 3D model satisfactorily predicts the water level in the contraction and the maximum water depth but under-predicts the amplitudes of the standing wave troughs in the downstream prismatic section.