Experimental study of the effect of splitter blades on the performance characteristics of Francis turbines

Abstract

With the improvement in energy structures, the safe and stable operation of hydropower units is becoming the most important issue for electric grids. To expand the stable operating range of a 200 m head Francis turbine, splitter blades were designed to increase the cavitation ability and lower the high-amplitude pressure fluctuations. Experimental studies were carried out to analyze the effect of the splitter blades on the turbine performance characteristics (efficiency, cavitation, and pressure fluctuation), and the results obtained were compared with those for normal blades. The results reveal that the splitter blades can increase the efficiency by approximately 2%, and they can reduce the pressure fluctuation in the vaneless space, under high-head operating conditions. The flow observation results reveal that the splitter blades can restrain the cavitation at the suction side of the blades, and thereby expand the stable operating range. Analyses of the pressure fluctuation show that the splitter blades can change the blade passing frequency and sharply lower its amplitude. This study may provide a reference for all Francis turbine designs, which makes it significant for the stable and effective operation of hydropower units.