Vortex-induced autorotation potentials of bladeless turbine models

The autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number.