Development of a propeller-type hollow micro-hydraulic turbine with excellent performance in passing foreign matter

This study develops a micro-hydraulic turbine with excellent performance in the passage of foreign matter included in the water flow. The runner has four blades, with a circular hollow around the rotating axis to pass foreign matter through the runner. The ratio of the hollow diameter D2 to the runner outer diameter D1, D2/D1, is defined as the hollow ratio ε. Laboratory experiments are conducted by introducing polyester fibers into the water flow as foreign matter. The turbine efficiency η decreases with increasing ε under the fiber-free condition. For the runner having no hollow (ε = 0), η decreases drastically with increasing the mass of the introduced fibers. This is due to the blockage of the runner by the fibers. But η for the runners provided with the hollow decreases less. This demonstrates that the hollow makes the fibers pass successfully through the runner. Additional experiments are conducted using the runner with ε = 0.25. The blade leading edges near the central axis are rounded with radius R. When R/D1 = 0.1875, the decrease in η due to the fibers is extremely small. The rounded leading edges successfully prevent the runner from catching the fibers, demonstrating that they effectively heighten the passage performance of foreign matter through the runner.