On the Effectiveness of Pylon Fairing Profiles in Minimizing Inflow Disturbance for a Downstream Tidal Turbine Rotor

Abstract:

Tidal stream turbines (TST’s) are energy harvesters designed to be deployed in turbulent inflow environments that pose some challenges to their operational efficiency and longevity. Additionally, TST’s with a downstream rotor (like Verdant Power’s Gen5 KHPS) encounter fluctuating loads and a persistent velocity deficit due to the upstream pylon, that further trims power output and accelerates fatigue damage to the turbine blades and other components. The ongoing collaboration between Lehigh University and Verdant Power seeks to minimize the downstream velocity deficit and fatigue damage to the rotor blades by testing the effectiveness of various pylon fairing profiles using laboratory experiments that mimic turbulent inflow environments representative of tidal energy sites. The Tidal Turbulence Testing facility housed at Lehigh University is equipped with a Makita-type active grid turbulence generator. The active grid comprises of ten rotating winglet shafts with a total of sixty rotating winglets; a dedicated stepper motor controls each shaft. Preliminary studies on the active grid have demonstrated the ability to tailor turbulence statistics such as the turbulence intensity, Taylor Reynolds Number, and integral length scale over a range of values representative of highly energetic tidal energy deployment sites. Candidate pylon configuration was tested at a Reynolds number of 5.3 × 10⁴ and a turbulence intensity of 12.5%. A simple circular cylinder was tested as the baseline pylon; modified pylons incorporated straight and concave fairings. Additional pylon configurations involving fairings oriented upstream, yawed fairings as well as fairings both upstream and downstream, referred to as the double fairing was also tested. From the data collected, it was observed that a yawed double fairing was the most beneficial fairing configuration; it considerably minimized the downstream velocity deficit and partially steered the wake away from the rotor. The double fairing also proved to be the most effective in eliminating pylon induced downstream flow periodicities.

Acknowledgments: The authors thank the US National Science Foundation for financial support for this project (PFI-TT Award #1919184 from Division of Industrial Innovation and Partnership).