Numerical simulation of flow instabilities in steep, stepped channels

摘要

This study deals with flow instabilities in steep, stepped channels. The origin of the research is based on an incident during a twenty-year flood at the river Ruetz in Tyrol, Austria. During this flood event flow instabilities occurred which lead to the overtopping of the riverbanks and the damaging of the revetments. An extensive study on a physical model was carried out. Velocity and water depth measurements in physical models can only be obtained with limited resolution and boundary conditions are hard to control and to modify. In numerical models flow conditions can be determined at each point of the computational mesh and complete control of boundary conditions is possible. In a first step two-dimensional investigations were undertaken in order to verify appearance of flow instabilities for the numerical approach. Three-dimensional runs were performed in order to verify the numerical model. Finally different scenarios were calculated and evidence on the origin of flow instabilities in steep stepped channels was found.