NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Numerical Modelling of Tidal Turbines
Darren Coppinger, Dr Stephen Nash
Civil Engineering (and Ryan Institute), College of Engineering & Informatics, NUI Galway
darren.coppinger@nuigalway.ie, stephen.nash@nuigalway.ie
Abstract
Tidal current energy resources have the potential to
provide a sizable proportion of Ireland’s energy;
however, the technologies required to utilize tidal
stream resources and deliver energy on a usable scale
are very much at a developmental stage. More
importantly, while promoted as ‘clean’ energy
technologies, the siting of marine renewable energy
devices in estuarine and coastal waters will alter
current flows and water levels, and therefore has the
potential for adverse environmental and economic
impacts. The main objective of this research is to
develop a generic numerical model capable of
simulating energy extraction from coastal waters via
tidal turbines. The model will then be used to assess the
hydro-environmental impact of turbine deployments. A
nested three-dimensional hydrodynamic model will
allow spatial resolution at device-scales thus enabling
accurate assessment of turbine yields and impacts.
1. Introduction
Tidal current energy resources can provide a sizable
proportion of Ireland’s energy. By utilizing this
indigenous, sustainable resource we can reduce our
over-reliance on fossil fuels. The siting of tidal stream
energy devices in coastal waters has the potential for
adverse hydro-environmental impacts. The primary
objective of this research is to develop a generic
numerical model capable of simulating the effects of
energy extraction (via tidal turbines) on coastal waters.
2. Research Aims
The aims of this research are as follows:
1. Develop a 3D numerical model to simulate the
effects of tidal turbine power extraction
2. Investigate effects of power extraction on
hydrodynamics (i.e. currents and water levels)
3. Investigate and optimize configurations of turbine
farms for maximum yield and minimum impacts
4. Determine optimum conditions for turbine
deployment sites
3. Research Methodology
The DIVAST (Depth Integrated Velocity And Solute
Transport) model will be used for this research. The
following methodology will be employed:
1. Develop 2D nested model
2. Incorporate tidal turbines into model
3. Develop 3D nested model
4. Incorporate turbines into 3D model
5. Use 2D and 3D models to investigate far-field
effects of power extraction
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4. Nesting Technique
Nesting techniques allow the use of high resolution
within particular regions of interest, while lower
resolution is used elsewhere in the domain. This
research aims to build on a novel nesting technique
previously developed at NUI Galway. Figure 1
illustrates the nesting process. The area of interest,
where higher resolution is desired, is highlighted in a
deeper blue. A high resolution grid is specified in this
area of interest. This “child” grid uses the results of the
lower resolution “parent” grid as boundary conditions.
Figure 1: Diagram showing the turbine model contained within the
nested grid of the model domain.
5. Turbine Modelling
Horizontal axis tidal turbines can be modelled as an
actuated or porous disc. This method is useful as the
complex geometry of the turbine need not be fully
specified. The actuated disc applies a thrust force to the
moving fluid; this force can be incorporated in the
governing equations of flow to simulate the extraction
of energy from the flow by a turbine. The thrust from
the disc to the flow can be derived as:
T = ½ ρCTAu 2
where:
T = thrust from the turbine to the fluid
u = velocity
ρ = fluid density
A = area of the turbine defined as an actuated disc
CT = coefficient of bypass and turbine wake flow
6. Conclusion
The development of accurate numerical models for the
assessment of tidal current energy resource, power
extraction and the hydro-environmental impacts of
power extraction is important for the development of
the tidal turbine industry.