The behaviour of Tidal Stream Turbines (TST) in the dynamic flow field caused by waves and rotor misalignment to the incoming flow (yaw) is currently poorly understood. The dynamic loading applied to the turbine could drive the structural design of the power capture and support subsystems, device size and its proximity to the water surface and sea bed. In addition, the strongly bi directional nature of the flow encountered at many tidal energy sites may lead to devices omitting yaw drives; accepting the additional dynamic loading associated with rotor misalignment and reduced power production in return for a reduction in capital cost. For such a design strategy it is imperative to quantify potential unsteady rotor loads so that the TST device design accommodates the inflow conditions and avoids an unacceptable increase in maintenance action or, more seriously, suffers sudden structural failure. The experiments presented as part of this work were conducted using a 1:20th scale 3-bladed horizontal axis TST at a large towing tank facility. The turbine had the capability to measure rotor thrust and torque, blade root strain, azimuthal position and speed. The maximum outof- plane bending moment was found to be as much as 9.5 times the in-plane bending moment, within the range of experiments conducted. A maximum loading range of 175% of the median out-of-plane bending moment and 100% of the median in-plane bending moment was observed for a turbine test case with zero yaw, scaled wave height of 2m and intrinsic wave period of 12.8s. A Blade Element Momentum (BEM) numerical model has been developed and modified to account for wave motion and yawed flow effects. This model includes a new dynamic inflow correction which is shown to be in close agreement with the measured experimental loads. The gravitational component was significant to the experimental in-plane blade bending moment and was included in the BEM model. Steady yaw loading on an individual blade was found to be negligible in comparison to wave loading (for the range of experiments conducted), but becomes important for the turbine rotor as a whole, reducing power capture and rotor thrust.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:588910 |
| Date | January 2013 |
| Creators | Galloway, P. W. |
| Contributors | Bahaj, Abubakr |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/361524/ |
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