Impact of macro-turbulent structures from mooring anchors and rough riverbeds on the performance of a horizontal axis hydrokinetic turbine
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Date
2018
Authors
Ekezie, Sixtus
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Abstract
Reported are laboratory and field measurements obtained to characterize the flow structures caused by mooring anchors and rough river beds on the performance of
hydrokinetic turbines. Series of flow velocity profile in-situ measurements characterize
the energetic flow at the Canadian Hydrokinetic Turbine Test Centre (CHTTC)
located on the Winnipeg River. Using an acoustic Doppler velocimeter, a novel
method was applied to obtain the flow velocity through the water column to contribute
to the design and optimization of power production from a hydrokinetic turbine. The
acoustic Doppler velocimeter measures the mean and fluctuating velocity components
at a frequency of 64 Hz. Tests were performed between 2.1 and 2.7 m/s upstream
and downstream of turbine mooring anchors. Anchors occupy 12% of the water
column height. Near-surface measurements show a 9.9% increase in turbulence
intensity and 8.8% increase in free-stream velocity due to the upstream turbine
mooring structures while the profile measurements show a temporal variation in the
velocity and turbulence intensity profiles. In a more detailed laboratory investigation,
four different scaled geometries of turbine mooring anchors were designed, fabricated
and tested, including a 19.8 cm diameter horizontal axis turbine in a water tunnel.
Tests are first performed at a steady velocity of 1.1 m/s and at an unobstructed
Reynolds number of 217000 based on rotor diameter. During this testing, velocity
measurements were taken at different locations upstream of a scaled horizontal turbine
to determine the optimum operating conditions in a steady free-stream velocity.
Furthermore, 25 surface roughness and four mooring anchor geometries were tested
and located 2 and 3 rotor diameter upstream of the turbine in the water tunnel.
Results show a 14% to 36% increase in turbine performance due to the impact
of mooring anchor geometries and surface roughness. These results are useful in
choosing a turbine mooring anchor design, geometry, and location to enhance turbine
performance and obtain an understanding of a rough riverbed at the energetic river
site.
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Keywords
Macro-turbulent structures, Turbine mooring anchors, Water tunnel