An experimental investigation of the air injection effect on the vortex structure and pulsation characteristic s in the Francis turbine

Abstract

The paper studies the pulsation characteristics of the flow when operating a medium scale hydrodynamic test bench with a Francis turbine. The pressure fluctuations measurements and flow st ructure visualization were performed for all operation modes of the hydraulic unit. To control and suppress pulsations in the flow path, a series of experiments on air injection to the hydraulic unit were carried out. Comparison of pressure pulsations for single phase and two phase flow experimentation has shown that for modes with maximum loads, the pressure pulsations can be reduced almost to a half by means of air injection. The effect of air injection is also studied with respect to the efficiency of th e hydraulic turbine.