Abstract
Cavitation and system instability are the most common problems occurring in hydraulic power systems, especially operated under part-load conditions. Previous research show that when the hydraulic turbine operates apart from designed conditions, such as part-load conditions, a helical vortex rope occurs from the runner exit, and usually generates severe pressure oscillations. Cavitation usually appears and turns the rope to become a two-phase cavitation rope. The occurrence of cavitation rope is believed to be the main reason of the severe pressure oscillations. Based on a new multiphase flow simulation method re-developed in ANSYS CFX, this paper did the runner modification by using grooves and made the investigation of pressure fluctuation alleviation in a hydraulic turbine at different cavitation numbers. The behavior of cavitation rope and the pressure fluctuations induced by cavitation under typical part load conditions with modified runner were analyzed in present research. The results show that besides the pressure fluctuation induced by the rope rotating, cavitation induced a new pressure fluctuation with a lower frequency. For the embedded analysis the results show that the modified runner can decrease the vortex rope eccentricity and increase the vortex core pressure and finally alleviate the two types of pressure fluctuations. Also, the turbine efficiency has a little rise when equipped with the modified runner.
Highlights
High quality and safe power is an important guarantee for industrial production and people’s daily life
Hydraulic power has some advantages of easy storage and flexible power generation, so it plays a role of power control of the grid, making it an irreplaceable power source in the electrical grid
The emphasis was on the vortex rope behavior and pressure fluctuation alleviation
Summary
High quality and safe power is an important guarantee for industrial production and people’s daily life. Developing renewable sources such as water energy, wind energy, nuclear energy are the main directions to generate electric energy. Water energy converted to electric energy has advantages of low pollution and recycling. Hydraulic power has some advantages of easy storage and flexible power generation, so it plays a role of power control of the grid, making it an irreplaceable power source in the electrical grid. It is a fact that operating conditions of hydro turbines is in a wide range [1]. When hydraulic turbines operated at part-load conditions, a series of negative problems such as high amplitude pressure fluctuations, dominant frequency and secondary flow occurred. Cavitation and system instability are the most common problems occurring in hydraulic power systems [2]
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