Abstract
This article proposes an experimental apparatus design to measure the power of a cross-flow marine hydrokinetic turbine system operating in a laboratory water tunnel. Data, from one Hall sensor output signal, was processed to capture the three types of torque exerted on the turbines: mechanical loss, brake, and hydrodynamic torque. The method was then applied to compare the power of a twin turbine system in different counter-rotating configurations. Controlled by a hysteresis brake, the tip-speed-ratio was varied in a constant freestream velocity of 0.316 m/s. While the braking torque was independent of the speed, the mechanical loss was found to depend on the system rotational speed and the amount of mass mounted on the mechanical support. In a counter-rotating configuration, the turbines were synchronized through a pair of spur gears and timing pulleys. Operating at the average chord based Reynolds number of 8000, each turbine had three NACA0012 blades mounted at 15∘ pitch angle. The power coefficient results of 8 turbine configurations showed the tendency of power enhancement of counter-rotating configurations due to blade interaction and increase in blockage ratio. Comparison of the results suggested direct application in a river flow scenario and manipulation of the blade interaction for optimal power production.
Highlights
In 2017, the hydroelectric power sector centering around hydraulic turbines occupied approximately 60% of the whole renewable energy market, which was expected to grow up to $1510 billion until 2025 [1]
Using a single Hall effect sensor, this methodology can be applied to measurements of the mechanical loss in any rotating mechanical system, the torque generated by an electromagnetic brake, and the hydrodynamic torque exerted on an marine hydrokinetic (MHK) turbine
The mechanical loss measurements showed that frictional torque due to bearings are rotational speed dependent and a simple linear assumption of the system deceleration curve could lead to more than 10% error in measurements
Summary
In 2017, the hydroelectric power sector centering around hydraulic turbines occupied approximately 60% of the whole renewable energy market, which was expected to grow up to $1510 billion until 2025 [1]. There was no correlation between the amount of mass mounted on the turbine shaft versus the mechanical loss which contributed to the uncertainty of the torque measurement Another attempt with small scale turbine experiments, which were conducted in the same water tunnel facility as used in this article, made use of a DC motor manufacturer torque curve for turbine power measurements [34]. The resisting torque exerted on the turbine system by the hysteresis brake was measured directly at different input voltage Taking advantage of this novel experimental approach and the small laboratory scale, power production of two identically manufactured MHK turbines were measured independently and together as a synchronized counter-rotating system in different configurations
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