Simulation of the structural behavior of a Francis runner in Deep Part Load Operation

Abstract

Abstract With the need for flexible operation, Francis runners are exposed to various operating conditions beyond the traditional operating range. These machines have to be designed for long time Part Load Operation in order to meet hydraulic and structural requirements. Deep Part Load Operation (DPL) mainly consists of stochastic loads on the blades. Whereas calculation methods for the dynamic stress at full load operation are well established, calculation of the dynamics during low load operation are in the focus of current research to increase the prediction accuracy. An unsteady flow simulation has been performed for a deep part load operating condition with the goal to derive the time-dependent pressure distribution in the runner. Based on the results, a FEA simulation with a 360° model is performed for multiple time steps to calculate the structural behavior. For a subsequent comparison to a strain gauge measurement, relevant characteristics with regard to material fatigue are identified. In addition, the calculation time in relation to the accuracy of the main characteristics of the flow induced stresses will be discussed.