Design and characterization of a vertical-axis micro tidal turbine for low velocity scenarios

Highlights: • Hydrokinetic turbine model designed to optimize the operation at low water velocity. • Experimental tests in a channel with different water upstream velocities. • Peak power depends on the upstream velocity and is linked to the blockage intensity. • Results are similar to those obtained by using the Momentum Actuator Disk theory. • A relation between turbine performance and channel slope has been obtained. Small tidal turbines are considered economical and reliable for distributed electricity generation. Low initial cost and ease of installation make them cover all sides of the economic viability triangle in the energy market. However, operating these turbines under realistic tidal velocities remains a great challenge. The work presented herein involves the design and assessment of a micro vertical axis hydrokinetic turbine, operating at low water velocities. The blade profile, solidity and aspect ratio of the turbine model have been selected looking for a self-starting and efficient operation. Thanks to the continuous development in the additive manufacturing technology, the model can be precisely fabricated at a fraction of the cost offered by traditional machining technologies. Experiments have been performed at three flow rates with a range of inlet velocities from 0.3 to 0.7 m/s. Power curves have been obtained for each operating condition, from zero load up to the point of maximum power. Additionally, the non-dimensional tip speed ratio and power coefficient have been used to compare the performance of the different parameters. It has been found that the upstream velocity has the most obvious effect on the turbine performance, and that the peak power coefficient is linked to the intensification in the blockage ratio. Furthermore, the actuator disc theory adjusted for open channel flow has been compared and found in consonance with the experimental results. This theory has also been employed to define the turbine efficiency which, from 0.45 m/s upwards, is over 70%, and as high as 81%. Finally, the performance in an inclined channel has been analysed, finding the correlations of the maximum power points and their corresponding tip speed ratios as a function of the slope.