Performance Optimization of Overshot Water Wheels at High Rotational Speeds for Hydropower Applications

Abstract

Overshot water wheels are hydropower converters generally employed for head differences up to 6 m and maximum flow rates of 150−200 L/s per meter width. The maximum hydraulic efficiency (80%–85%) is constant for rotational speeds below the critical speed, whereas the efficiency linearly decreases at higher rotational speeds due to the increase of water losses at the inflow. To improve the efficiency when the rotational speed is above the critical speed, an improved geometric design was investigated by implementing a theoretical model validated using experimental results. The new geometry consists of a circular wall around the periphery of overshot water wheels. The wall redirects into the buckets the water flow that is lost at the inflow, improving the efficiency up to 1.5 times at high rotational speeds.