Investigation of the Pressure Fluctuation Alleviation in a Hydraulic Turbine by Runner Modification

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.

Analysis of Flow Field Characteristics and Pressure Pulsation in Horizontal Axis Double-Runner Francis Turbine

“…Different numerical models will have a significant impact on the accuracy of calculations, and the selection of an appropriate turbulence model can capture the required flow details more accurately [35]. The Standard k-ε turbulence model may lead to negative normal stress when the time-averaged strain rate is particularly large.…”

State-of-the Art-Powerhouse, Dam Structure, and Turbine Operation and Vibrations

“…The authors designed a new siphon turbine based on the original distributor and runner, which led to the best design with a bell-shape distributor, four guide vanes, and the highest power output at the lowest head [194]. Modification of the runner using grooves can reduce vortex rope eccentricity and increase the vortex pressure, ultimately increasing the turbine efficiency [195]. In another study, the stability power output of hydro-turbines, which included energy losses, sensitivity analysis, and distribution features of the losses with an elevated guide vane, was considered.…”

“…Various designs have been proposed to enhance the hydro-turbine efficiency, which have been tested via numerical simulations [146,163,168,177,178,[195][196][197][201][202][203]. Vibration due to powerhouse operation has been analyzed by several researchers [151,176,[201][202][203]205,206,208,209,226]; however, more comprehensive studies should be completed to connect the effect of vibration from turbines operation with design on the dam body, to assure dam safety.…”