Cm-scale axial flow water turbines for autonomous flowmeters: an experimental study

This paper reports on the performances and the optimization of a 40 mm diameter water flow energy harvester based on an axial turbine (horizontal axis propeller) coupled to a customized permanent magnet generator. To the best of our knowledge, this work is one of the first comprehensive studies in the low dimensional and flow velocities ranges. The parameters of the propeller have been empirically optimized (\(\lambda_D\)=1, B=4 blades) by the means of experiments in a test-bench pipe at various flow rates from 1 to 9 m3 h−1. The best propeller design has been selected for its performances in terms of electrical power and pressure drop. A customized permanent magnet converter with ferromagnetic elements has been modeled, optimized with finite elements simulations and fabricated. This has enabled to increase the electrical power by 2.7 @ 1.5 m3 h−1 (3.2 mW) and up to 14.1 @ 9 m3 h−1 (490 mW) compared to a simple magnet-air coil converter. The figure of merit of our water flow harvester, which takes the electrical power and the pressure drops in the pipe into account, is greater than previously reported water flow energy harvesters, and corresponds to an overall mechanical-to-electrical conversion efficiency of 5.15%.