Author(s): W Weber

Linked Author(s):

Keywords: Francis turbine; Shaft line dynamics; Runner side chamber; Bulk-flow model; Added mass effect

Abstract: The analysis of dynamic fluid behavior in runner side chambers of Francis turbines to estimate the effect on the shaft line behavior is presented. The shaft line analysis of hydropower units is carried out to ensure stable behavior of the shaft line as well as a smooth vibrational behavior. At first, mechanical stiffness and mass properties of rotating and non-rotating components of the power unit as well as oil-film properties are necessary parameters for the shaft line modelling. In hydropower, the fluid inside and around the turbine runner can also have a relevant influence on the shaft line behavior. Here, the added mass effect is well known in hydropower engineering. Sometimes, high shaft vibrations due to a self-excitation mechanism have been observed at hydropower units that were caused by the leakage flow of the fluid around a Francis runner. Therefore, the consideration of the effects of the surrounding fluid on the shaft line is a serious topic for a reliable dynamic shaft line assessment. In this contribution, the fluid flow in the runner chamber at the band of Francis runners is investigated. The fluid behavior is described by bulk-flow models, in which average velocities and pressures over the clearance are used. The non-linear flow behavior is solved in two steps. First, a non-linear analysis is performed to calculate the steady state flow field for centric position of the rotor. Second, a linear perturbation analysis for the moving rotor is carried out to derive parameters for the shaft line analysis. Results of this approach will be compared to ones obtained by CFD.

DOI: https://doi.org/10.1088/1755-1315/1483/1/012030

Year: 2023