3-D computation of flood processes in sharp river bends

Abstract

Three different three-dimensional computational fluid dynamics codes—SSIIM, Fluent and RSim-3D—were used to predict water surface and flow field during the 100-year flood of August 2002 in a sharp bend of the Danube River near the Austrian municipality of Grein. All models solved the Reynolds-averaged Navier–Stokes equations using a finite-volume approach. For the SSIIM and Fluent models, a structured grid of hexahedral cells was employed, while the basis for the RSim-3D model was an unstructured grid of arbitrary polyhedrons. The non-hydrostatic pressure field was computed using the Simple method and the standard k−ε model provided turbulence closure. The position of the water surface was derived from the pressure field. Computed water surface elevations were compared with each other and verified using field data observed during the flood event. It was found that the maximum super-elevation of bank water levels was predicted within an error margin of 10–20% of the observed value. Flow velocity magnitudes were found to vary among the different models, which is primarily credited to different pressure distribution schemes. Strong secondary motions with velocity magnitudes of up to 1 m/s were predicted by the computer codes, contributing to the extreme super-elevations observed.