Gareth Huxham

BE (Mechatronic),
PhD Research Student
Environmental Fluids Group


School of Civil Engineering, Room 101
Phone: 0402 435 653
Fax: +61 2 9351 3343
Email: ghux5691@usyd.edu.au

Research project - Energy extraction from laminar and turbulent flows by biomimetic hydrofoil

Supervisor: Dr Tim Finnigan
Associate Supervisor: Dr. Stefan Williams (Australian Centre of Field Robotics)

Tidal energy is a largely untapped renewable energy resource. It has an advantage over other intermittent renewable energy sources such as wind and solar in that it is highly predictable. Tides in a given location can be predicted with high accuracy for a period of over 20 years.

Tidal In-Stream Energy Converters (TISECs) being developed to harness tidal energy promise lower environmental impacts than traditional tidal barrage power plants that dam an estuary or river mouth. One class of TISEC receiving commercial interest is the oscillating foil energy converter (OFEC). This type of device operates by passive or active pitch manipulation of one or several hydrofoils to generate lift forces to drive an oscillating heave of the foil(s). This heaving motion may be coupled to a generator to extract energy from the flow.

While significant advances have been made through CFD simulations of OFECs there has been relatively little experimental research in the area. In particular there is little published experimental research on the elastically supported OFEC, a type of OFEC being commercially developed by 2 tidal energy companies.

To address this need experimental research was conducted of an elastically supported Oscillating Foil Energy Converter (OFEC). The device mimics aspects of fish locomotion to extract energy from tidal streams. A model OFEC was designed, installed and tested in a customised water tunnel testing facility. The objective of the tests was to investigate the influence on power generation and efficiency of key dimensionless parameters; the reduced frequency (k), pitch amplitude (α0), and damping coefficient C’.

Tests have achieved an efficiency of 27%, demonstrating the potential of the device to efficiently harness clean, renewable energy from tidal streams. Inspired by nature, the device promises a new means to harness tidal energy while offering lower environmental impacts than traditional barrage tidal power plants.

Inspired by nature
Through natural selection fish have evolved highly efficient modes of locomotion. The Thunniform swimming mode, employed by top ocean predators such as tuna and shark, is characterized by a large lateral motion of a stiff caudal fin. Efficient thrust is achieved through the controlled generation and shedding of vortices from the fin. The OFEC mimics aspects of this swimming motion to extract energy from a flow. The caudal fin and tail of a fish are represented by an oscillating hydrofoil on a swinging lever arm.

Commercial developments in OFECs
Commercial developments in OFECs included the 150kW Stingray demonstrator installed in Yell Sound in 2003, the 100kW Pulse Stream 100 prototype commissioned in the Humber River in 2009 and the 250kW BioStream demonstrator being developed for installation in Australia, shown in the following figure.

Artists impression of the BioStream oscillating foil tidal stream energy converter being developed by BioPowerSystems biopowersystems.com


How it works
The following diagram illustrates the operation of the elastically supported OFEC.

Experimental model
The following diagram illustrates the model OFEC that was designed and installed in a water tunnel testing facility in the Civil Engineering Fluids Lab.

Results
Experimental tests of the elastically supported OFEC have demonstrated the potential of the device to harness energy from flows. Tests achieved an efficiency of 27.3%. This peak efficiency occurred at a pitch amplitude of α0 =58° and reduced frequency of k = 0.1. This is in good agreement with numerical research of OFECs undergoing a prescribed pitch and heave.

A contour map of efficiency is shown in the figure. There is a well-defined region of peak performance. Maximum efficiency occurred at high pitch amplitudes in a region of deep stall. In this region vortices generated on the foil dominate the flow field and enhance efficiency by increasing the magnitude of unsteady transient lift forces. This is somewhat analogous to fish swimming where vortices shed from the tail enhance propulsive efficiency.

Selected publications

• Experimental Parametric Investigation of an Oscillating Hydrofoil Tidal Stream Energy Converter. 18th Australasian Fluid Mechanics Conference Launceston, Australia 3-7 December 2012
• University of Sydney Launches into Ocean Energy Research Waves, Volume 14, Number 1, p8, 2008

Learning and Teaching Duties

• CIVL2611 Fluid Mechanics
  CIVL3612 Fluids & Environmental Engineering
  CIVL3010 Engineering & Society
  CIVL2201 Structural Mechanics