The Effect of Guide Vane Airfoil of Medium Specific Speed Francis Turbine on Pressure Pulsation inside Vaneless Space

The matching rationality of the guide vane airfoil with the runner has many influences on hydraulic performance of hydraulic turbine. In some of the small and medium-sized power plants that have been built,due to the unreasonable selection and design of the flow passage of the power station,the airfoil of the guide vane does not match the runner,resulting in a prominent problem of pressure pulsation in the vaneless space. In order to study the influence of guide vane airfoil on the pressure pulsation vaneless space of the medium specific-speed Francis turbine,a medium specific speed（ns=190）Francis turbine that needs to be modified is taken as an example. Numerical simulation of three-dimensional transient flow field is performed on the turbine flow passage which composed of three guide vane airfoils,with negative curvature,symmetrical and negative curvature and the same runner under different heads. The influence of matching different types of guide vanes on the hydraulic performance of the turbine is analyzed,focusing on the influence of the pressure pulsation in the vaneless space. The results show that the use of negative curvature guide vanes for the medium specific-speed Francis turbines that need to be modified has a significant effect on the improvement of efficiency and output. Due to the increase in the vaneless space of the medium specific-speed Francis turbine,the pressure pulsation in the vaneless space is more complicated. The low-frequency pulsation of the turbine with the guide vane of negative curvature is improved compared with that of the turbine with the other two airfoils,and the periodicity and regularity of the circumferential pressure pulsation are also better.