An Experimental Investigation of the Air Injection Effect on the Vortex Structure and Pulsation Characteristics 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 structure 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 the hydraulic turbine.