Prediction on the pressure pulsation induced by the free surface vortex based on experimental investigation and Biot-Savart Law

Free surface vortex (FSV) is a negative phenomenon in pump stations and hydropower stations. The purpose of this paper is to investigate the pressure pulsation induced by FSV. Firstly, a theoretical model of linear vortex-induced pressure pulsation was established based on Biot-Savart Law, which changes periodically with time in the form of trigonometric function. A high-speed camera is used to obtain the evolution process of FSV, which is divided into five stages: inception, development, continuance, collapse and disappearance. In the stages of development, continuance and collapse, FSV develops into an inspiratory vortex. In the continuance stage, FSV continues to inhale, with the largest scale and the most harmful to the unit. The analysis shows that FSV conforms to the linear vortex characteristics. According to theoretical analysis and model experiments, the pressure pulsation induced by FSV includes two parts: the induced pressure pulsation by rotating-disturbances with induced frequency in 2.32-2.48Hz and the pressure pulsation induced by inspiratory-disturbances with induced frequency in 5.62-5.83 Hz. The pressure pulsation induced by FSV is a low-frequency pulsation, which can easily induce resonance of the unit. The study offers a new basis on the pressure pulsation induced by the free surface vortex.

Automated summary

This paper investigates the pressure pulsation induced by free surface vortex (FSV) in pump and hydropower stations. The study establishes a theoretical model based on Biot-Savart Law and identifies two parts of pressure pulsation induced by FSV: low-frequency pulsation caused by rotating disturbances and high-frequency pulsation caused by inspiratory disturbances. The findings provide valuable insights on the resonance-inducing effects of FSV.