Bio-inspired morphing blades for wind and tidal turbines

The blades of axial-flow horizontal-axis tidal and wind turbines experience continuous variations of the angle of attack and flow speed. This is due to the vertical shear layer, the turbulence of the free stream, tower shadow, yaw misalignment, blade oscillations and wakes of upstream turbines. With the scale up to larger and larger turbines, and the increase use of floating platforms, flow fluctuations are set to further increase [1,2]. In fact, both wind and tidal turbine diameters become closer to the size of the most energetic turbulent eddies in the flow stream [3], and the increase in blade flexibility leads to higher aeroelastic coupling [4]. Flow fluctuations are particularly large for tidal turbines due to the high turbulent kinetic energy in the tidal stream and of the wave-induced current. This results in thick and expensive structures with short fatigue life, which are key issues for the wind and tidal energy sectors. In particular, while decreasing load fluctuations is critical for the wind industry in order to decrease the levelised cost of energy [5], reliability is one of the main technological goals of the tidal industry [6]. The current reliability of axial tidal turbine blades has been estimated in one failure every two years, while the expected lifetime of a turbine should be 20 years [7]. For comparison, on wind turbines, the blade failure rate is only one in every ten years [7].

The remarkable flight control of some species of birds when flying in strong gusty wind is due to the sophisticated control of their wing shape. This concept is well understood and mimicked in aeronautics, where the shape of aircraft wings continuously changes to increase fuel efficiency and maximum payload [8]. Similarly, sailing crafts experience very large flow fluctuations but are capable to maintain a constant heel and transform gusts into forward accelerations. When a gust hits the craft, the sail and the rigging deform elastically accumulating potential energy, which is then transformed into forward thrust through a slow elastic displacement. Conversely, wind and tidal turbine blades are rigid and have a high inertia, and therefore the energy of flow fluctuations is transformed into fatigue load and vibrations. This affects the blades and the turbine, resulting in heavy and unnecessarily expensive structures [9].

The aim of this PhD project is to develop an intelligent blade that through a high-frequency shape morphing actuated with electroactive polymers, also known as artificial muscles, will cancel fatigue load. This will prevent fatigue failures of the blades, and fatigue loads transmitted from the blade to the turbine. The resulting blades and turbine will be lighter and less expensive, decreasing the levelised cost of energy. The focus of this project is to develop the underpinning fluid mechanics knowledge and perform proof of concept experiments to demonstrate the potentials of the proposed technology.

References

  1. P.B. Andersen. Load alleviation on wind turbine blades using variable airfoil geometry (2D and 3D study). PhD thesis, Technical University of Denmark, 2005. 

  2. T. Buhl et al. Potential load reduction using airfoils with variable trailing edge geometry. J. Sol. Energy Eng., 127(4):503–516, 2005. 

  3. E.A. Bossanyi. Individual blade pitch control for load reduction. Wind Energy, 6(2):119–128, 2003. 

  4. B.F. Ng, et al. Aeroservoelastic state-space vortex
lattice modeling and load alleviation of wind turbine blades. Wind Energy, 18:1317–1331, 2015. 

  5. T.K. Barlas and G.A.M. van Kuik. Review of state of the art in smart rotor control research for wind turbines. Prog. Aerosp. Sci., 46(1):1–27, 2010. 

  6. A. Badcock-Broe et al. Wave and tidal energy market deployment strategy for europe. Technical Report, 2014.
  7. T. Delorm. Tidal stream devices: reliability prediction models during their conceptual & development phases. PhD thesis, Durham University, 2014. 

  8. S. Barbarino et al. A Review of morphing aircraft. J. Intell. Mater. Syst. Struct., 22(9):823–877, 2011. 

  9. R.E. Murray et al. Passively adaptive tidal turbine blades: Design tool development and initial verification. Int. J. Mar. Energy, 2016.

 

Further Information: 

PIV measurements of the flow around a rigid and a flexible blade
PIV measurements of the flow around a rigid and a flexible blade

Principal Supervisor: 

Eligibility: 

Minimum entry qualification - an Honours degree at 2:1 or above (or International equivalent) in a relevant science or engineering discipline, possibly supported by an MSc Degree. Further information on English language requirements for EU/Overseas applicants.

Funding: 

Strong candidates may be considered for full EPSRC funding - open to UK/EU candidates only. Further information and other funding options.

Informal Enquiries: 

Closing Date: 

Tuesday, December 31, 2019