Modelling turbulent flow in two-stage meandering channels

Abstract

A three-dimensional (3-D) modelling study for calculating free-surface turbulent flow in two-stage meandering channels is presented. The numerical model solves the 3-D Reynolds-averaged continuity and Navier–Stokes equations with the k–ε turbulence model for steady-state flow. The flow equations are solved numerically with a general-purpose finite-volume code. The results are first evaluated against the experimental data obtained from the UK Flood Channel Facility. The predicted distributions of the free surface elevation, streamwise velocity, secondary vectors, turbulent kineti energy and bed shear stress are used to investigate the accuracy of the model prediction at both the apex and other sections along the channel. The predictive ability of the 3-D model is also assessed against results from a two-dimensional (2-D) model with regard to the distributions of free surface elevation, depth-averaged velocity and bed shear stress. The results show that the 3-D model predicts the flow fields reasonably well and estimates bed shear stress values more accurately than the 2-D model. The feasibility of applying the 3-D model to a practical field example is demonstrated for the case of an inbank flow on the River Blackwater. Here, the calculations are carried out for flow through a 130 m stretch of the River Blackwater for which detailed flow measurements were collected. The results show the ability of the 3-D model to capture the flow field with reasonable accuracy when applied to the complex boundary conditions which are needed to describe a semi-natural river. This illustrates the potential for using the 3-D model for predicting flow processes in natural rivers with complex geometry.