Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

Abstract

Pressure fluctuation at the vaneless space and vanes passages is one of the most important problems for the stable operation of a pump turbine. The fluctuation appears in any operating condition. Much research has been done on the pressure fluctuation of hydraulic machinery. However, the details of pressure fluctuation propagation of the pump turbine at the pump mode have not been revealed. The modern pump turbine with high water head requires the runner to be “flat”, which would induce pressure fluctuation more easily than the low head pump turbine. In this article, a high head pump turbine model is used as the research object. As the pressure fluctuation at off-design point is more serious than at the design point, the low head condition is chosen as the research condition. Pressure fluctuation at the vaneless space and vanes passages is predicted by the computational fluid dynamics method based on k-ω shear stress transport model. The experiment conducted on the test rig of the Harbin Institute of Large Electrical Machinery is used to verify the simulation method. It proves that the numerical method is a feasible way to research the fluctuation under this operating condition. The pressure fluctuation along the passage direction is analyzed at time and frequency domains. It is affected mainly by the interaction between the runner and vanes. In the circumferential direction, the influence of the special stay vane on the pressure fluctuation is got. The amplitude in the high-pressure side passage of that vane is lower than that in the other side. The study provides a basic understanding of the pressure fluctuation of a pump turbine and could be used as a reference to improve the operation stability of it.