FINDING FREE SURFACE OF SUPERCRITICAL FLOWS - NUMERICAL INVESTIGATION

A three-dimensional numerical model (STAR-CCM+) has been used to compute the free surface for different cases with supercritical flow. The program solves the Navier-Stokes equations on an unstructured hexahedral grid using the SIMPLE method and the k-epsilon turbulence model. The location of the free water surface has been computed with the volume of fluid method. Two cases from literature have been used for validation: one with a channel expansion and another with a channel junction. In both cases, oblique standing waves occurred. The geometry of the waves were well reproduced by the numerical model. The third case had a more complex geometry, modelling a physical laboratory study of a natural river geometry upstream of the dam of a hydropower plant. The case was unusual in that supercritical flow and oblique standing waves occurred upstream of the dam. Also for this case the numerical model gave reasonable results for the location of the free water surface.