Author(s): J Kahler; W Weber; M Schmid

Linked Author(s):

Keywords: Vortex rope frequencies; Francis-type turbines; Draft tube cone; Pressure pulsations; Air admission

Abstract: A relevant contributor to pressure pulsations at Francis-type turbines, especially at off-design operation, is the helical vortex rope and its interaction with the draft tube elbow. If the vortex rope frequency in such cases is close to the system’s natural frequency, resonance conditions are met and this can lead to undesired high pressure and, subsequently, power oscillations. Voith Hydro (VH) has therefore determined the frequency range of the helical vortex rope from model tests at VH laboratories with respect to the specific speed of the machine at its optimum. Subsequently, VH has investigated the potential benefit of air admission during such part-load operation in order to reduce the occurring pressure pulsations. This paper presents the results of the research carried out, introducing individual frequency bands for the vortex rope with respect to specific speed at optimum and the impact of air admission on pressure amplitudes. Results are verified using a 1-D simulation approach and by comparison with prototype commissioning data.

DOI: https://doi.org/10.1088/1755-1315/1483/1/012029

Year: 2023