Numerical and laboratory investigation of the hydrodynamic complexity of a river confluence

Abstract

The paper deals with the hydrodynamic investigation of the junction of two rivers in north-west Hungary in an urban area. The goal of the investigation was to study the flow conditions by means of a 3D k-ε turbulence CFD model and hydraulic scale model. The project gave the opportunity to compare the outcome of the distorted scale model with the ones of the CFD model in field scale, in the distorted hydraulic model scale as well as in undistorted scale, converting all the results to real field scale by assuming Froude similarity. Overall flow patterns, the effect of distortion and the robustness of the k-ε turbulence model in such complex confluence conditions were analysed. Satisfactory agreement was found except for the region straight downstream of the confluence where significant differences between laboratory and numerical results were seen due most probably to the complex swirling and shearing character of the flow. Large scale vortex formation interacting with anisotropic local turbulence would certainly need differential Reynolds stress turbulence closure.