Study on the characteristics of vortex motion and pressure pulsation in vaneless zone of Kaplan turbine

Abstract

Abstract Kaplan turbine with adjustable blade has wide operating efficiency and is widely used in medium and low head hydropower stations. Pressure pulsation has always been a key problem affecting the operating efficiency and stability of hydraulic turbines. The numerical simulation of the hydraulic characteristics of Kaplan turbine is carried out to analyze the pressure pulsation and flow distribution characteristic in the vaneless zone under different guide vane openings and blade installation angles. Results show that: At the small flow condition, vortices appear in the vaneless zone, which leads to the increase of pressure pulsation in the vaneless zone and the expansion of the fluctuation range of water moment on blade. At the small flow condition with different unit speed, the dominant frequency are observed to be between 4-5 times rotation frequency in the vaneless zone far from the runner inlet. The frequency source is that the rotating vortex flow and the rotating runner blade will form the effect similar to rotor-stator interference.The pressure pulsation observed at the monitoring point near the runner inlet mainly comes from the disturbance of the runner blade to the flow and the pressure pulsation frequency is 6fn .