Author(s): T. Mukai; M. Nakazono; T. Hashidate; T. Uchida; K. Tezuka; H. Koyama; J. Matsui

Linked Author(s): Tatsuhiko Uchida

Keywords: No Keywords

Abstract: This paper describes flow behavior which causes extraordinary transient stress on runner blade that occurs during start-up of a Francis turbine. Firstly, transient computational fluid dynamics (CFD) was conducted to evaluate hydraulic similarity for the condition of extremely low rotation speed and small guide vane opening. CFD results show that the pressure is below saturation vapor pressure all over the inside of the runner at extremely low rotation speed conditions. Secondly, model test was carried out to measure and evaluate pressure and strain on the blade. The test results revealed that there is a tendency that the phenomenon becomes more severe when rotation speed is lower, when guide vane opening is larger, and when suction pressure is lower. It is concluded that the extraordinary phenomena are not 'extraordinary' but commonly arisen as the transient hydraulic behavior and the impact load causing extraordinary stress on runner blades is related to the instantaneous condensation of vapor bubbles such as steam hammer accompanied by the explosive pressure rise.

DOI: https://doi.org/10.1088/1755-1315/1079/1/012023

Year: 2022