1. Lloyd’s Register Energy
Modelling techniques for tidal arrays
All Energy – Aberdeen
Lloyd’s Register
Marine Renewable Energy Research
Peter Davies
Global Technology Leader Renewable Energy
Energy Technology Directorate
Co presenter:
Morten Ryge Bøgild
Consultant
Energy, Fluid Dynamics
Lloyd's Register ODS
22nd & 23rd May 2013

2. Lloyd’s Register Energy
Agenda
• Introduction to Lloyd’s Register
• Previous work in tidal modelling
• Simulation goals
• Model setup
• Wave modelling techniques
• Steady state array simulations with and without waves

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Previous work in tidal modelling
• Modelling of tidal turbines using open source software - presented at All
Energy last year
• Modelling of tidal turbines using CFD both single turbines and arrays:
• The multipe rotating reference frames (MRF): Steady-state analysis,
produces a snap-shot in time (fast)
• The rigid body motion (RBM): Full transient solution for a rotating turbine
• See paper presented at Marine & Offshore Renewable Energy, 26-27
September 2012, London, UK

5. Lloyd’s Register Energy
Tidal velocity measurements
depth vs time
Update on EMEC activities, resource
description, and characterisation of
wave-induced velcities in a tidal flow
~Norris & Droniou 2007

6. Lloyd’s Register Energy
Tidal velocity measurements
depth vs time
Update on EMEC activities, resource
description, and characterisation of
wave-induced velcities in a tidal flow
~Norris & Droniou 2007

7. Lloyd’s Register Energy
Simulation goals
• Turbine loading and power performance
• Investigate and compare wake with and without waves
To do this:
• fully discretized numerical simulation of 3x3 tidal turbine array using STAR
CCM+ and ANSYS CFX.

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Modelling
• Domain size:
Width x length x depth:
540 x 560 x 45 m.
22.8 m
150 m120 m

9. Lloyd’s Register Energy
Modelling
• Inlet velocity profile:
• Mesh size in the order of 9 million for 3x3 array.
• Rotor may be stationary with rotating flow in the subdomain
around it; MRF.
• Or rotor may be rotating in a subdomain with mesh; Sliding
interface / RBM.
• Rotor speed adjusted to match generator:

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Steady state MRF
no waves
• Inlet velocity 2.5 m/s at hub height.
• Wake zone behind turbines reduces
velocity by 30 %.

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Settings
• Velocity profiles - modified by influence of
turbines

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Results
Array Layout

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Results
Array Layout

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Wave modelling
• Free surface waves
• Waves defined at the inlet – travels through the domain
• Computational intensive – diffusive if mesh is not refined in interface region
• Can model situations where waves are disturbed by the turbine
• Kinematic waves
• Waves are specified by velocity components at the inlet and the top boundary
• Able to model wave impact on tidal turbine but cannot model the tidal turbine effect on
the waves
Fig. from: Westphalen et al. “Simulation of Extreme Free Surface Waves using STAR CCM+ and CFX11” (2008)

15. Lloyd’s Register Energy
Steady state MRF
kinematic waves
• Inlet velocity 2.5 m/s at hub height. 3
m waves, T = 6 s.
• Wake zone behind turbines increases
velocity due to influence of
streamwise waves.

16. Lloyd’s Register Energy
Steady state MRF
kinematic waves
With waves
No waves

17. Lloyd’s Register Energy
Conclusion
• Fully discretized 3x3 tidal array modelling was simulated with and without
wave modelling using the MRF rotor simulation.
• Flow distribution and turbine performance in tidal array are possible outcomes.
• It has been demonstrated that the turbine wake is influenced by waves;
this is dependent on turbine design, wave height, period and water
depth.
• The choice of either modelling the free surface or using the kinematic
description depends on the above parameters.
• We are continuing to investigate the turbines influence on the free surface.
• We are continuing to compare STAR CCM+ and ANSYS CFX.

18. Lloyd’s Register Energy
ANY QUESTIONS ?
Thank you for listening

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