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Tidal Energy Research Group

The Tidal Energy Research Group is based in the Department of Engineering Science and conducts research in to clean, renewable energy generation from tidal flows. The group has a variety of active research projects spanning three main topics:

The group is multi-disciplinary and includes civil, mechanical and electrical engineers. The Group is also a contributor to Oxford University Climate Research.

The group has just secured a significant role in a major new multi-partner project funded by the Energy Technologies Institute to examine Performance Assessment of Wave and Tidal Array Systems (PerAWAT). The aim of the PerAWAT project is to accelerate the commercial deployment of wave and tidal energy convertors by developing numerical tools capable of accurately estimating the energy yield, and hence return on investment, of farms of wave and tidal energy convertors.

People

Research

Turbine Hydrodynamics and Tidal Resource Assessment

A very important feature of tidal power is that at present there are still considerable uncertainties to be resolved over assessment of how much power can be realistically extracted at a given site. We are working at every scale from a single device, through farms of multiple devices to entire tidal basins, to understand and optimise turbine performance and ultimate energy yield from a given tidal site.

At small scale we have demonstrated that the power that can be extracted by a tidal turbine is significantly higher than the "Betz limit" which restricts the total extractable power for an unconfined turbine such as a wind turbine. The Betz analysis is widely applied to the tidal case, but it underestimates the power because it does not take into account blockage effects in a gravity-driven flow of restricted depth.

At the device scale we use Computational Fluid Dynamics modelling to investigate flows through tidal turbines of various configurations ranging from simple axial and cross-flow turbines to novel design concepts. Recent work on cross-flow turbine hydrodynamics has brought new insight into the dependency of a device's performance on its geometric configuration; number of blades etc (Claudio Consul). Whilst modelling of flows through novel design concepts, such as those in which an outer duct is used to accelerate the flow through the turbine, is helping to develop a theoretical basis by which advanced design concepts can be assessed (Clarissa Belloni).

Localised interactions between devices are of great importance in determining the collective energy yield of a system of turbines, as wake effects can significantly reduce total energy yield. We are developing low order vortex wake modelling techniques to simulate and investigate turbine interaction effects (David Longworth).

At the tidal basin scale we are investigating the influence of power extraction on generic tidal systems (Scott Draper). Typical scenarios for high speed tidal flows (e.g. flow through a narrow channel, flow around a headland) are being simulated using the shallow water equations, and the effects of power extraction simulated so that optimal designs for tidal farms can be established.

Part of the group's activity is associated with developing high order numerical techniques that can be used to simulate various scales of tidal flow problems that support the group's wider research activities. Over recent years the group has developed high order Discontinuous Galerkin methods for solution of the Navier-Stokes equations for simulating device scale flows (Esteban Ferrer) and for solution of the Shallow Water equations for simulaing tidal basin flows (Scott Draper).

Transverse Horizontal Axis Water Turbine (THAWT)

THAWT is a unique device for exploitation of tidal current resources. Unlike most tidal turbines which look like variants of "underwater windmills" the flow in THAWT is transverse to the axis of rotation (see figure at top of page). Why do we pursue this solution? Our reasons lie in the economies of scale - in general, the larger a device can be made, the more economical it is (in terms of power per capital investment). This has resulted in a trend towards ever larger wind turbines (the largest are currently about 125m in diameter, delivering about 5MW). However, most high speed tidal flows are in relatively shallow water, and the diameter of an axial flow turbine cannot be made much larger without it breaking the water surface. The only way to make a tidal tubine in shallow water larger is to stretch it across the flow, and this can only be done with a horizontal axis, transverse flow device.

The most suitable transverse flow design is a "Darrieus turbine", but this suffers from the inherent disadvantage that it is a very flexible structure, and would suffer unacceptably large stresses and deflections if it were to be used as a tidal turbine of any significant size. Our solution to the problem is to realign the blades of the turbine to form an inherently stiff structure, allowing us to stretch the turbine to much larger dimensions. THAWT thus combines the efficient hydrodynamics of the Darrieus turbine, with a much stiffer and stronger structure.

We have completed a very successful set of model-scale tests in a flume at Newcastle University, and these tests have proven the hydrodynamic efficiency of the turbine. We are currently working on the analysis of the structure (Ross McAdam), refinement of the blade design (Claudio Consul) and numerical analysis of the turbine performance (Rachel Swidenbank).

We are actively pursuing the commercialisation of THAWT through Isis Innovation Ltd (the organisation that handles spin-out companies from Oxford University). A patent for the concept has been applied for. Discussions are being held with a number of interested parties.

Publications

Recent publications by the tidal group include:

Research Opportunities

We are actively seeking further research assistants and research students to work on all aspects of tidal devices. Enquiries regarding current vacancies should be made to richard.willden@eng.ox.ac.uk

Research Support

The group is variously supported and we are grateful to the following for their support:

 

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