FLOW ANALYSIS OF A RIVER CONFLUENCE WITH FIELD MEASUREMENTS AND RANS MODEL WITH NESTED GRID APPROACH

A comprehensive flow analysis for a confluence of two medium-sized (Q(mean)approximate to 30-50m(3)/s) Hungarian rivers was carried out by means of a three-dimensional Reynolds-averaged Navier-Stokes modelling. The model was validated against detailed fixed and moving Acoustic Doppler Current Profiler velocity profiling. Unsteady simulations with steady-state boundary conditions were performed on a structured grid in order to reveal the characteristic large-scale spatial behaviour of the flow, such as strong secondary currents because of the river bends upstream of the confluence. Secondary current vectors indicating the swirling character of the flow were derived both from field measurements and model results showing good agreements for two different discharge ratios. Additionally, a novel approach was used to simulate the unsteady vortex shedding implementing a nested grid into the previously used coarse grid. Using a considerable finer horizontal (similar to 0.5m) and time (1s) resolution, the numerical model reproduced the unsteady character of flow between the two rivers. A qualitative assessment of the mixing processes was also introduced through the example of the propagation of plaster plume used to neutralize a disastrous red mud spillage that occurred in 2010. The results indicate the combined influence of secondary currents and vortex shedding. Copyright (c) 2013 John Wiley & Sons, Ltd.