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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 22 nd & 23 rd May 2013

Peter Davies & Morten Boegild - Tidal turbine array modelling, influence of waves on turbine wakes

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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

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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

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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

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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

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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 m 120 m

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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)

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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.

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Steady state MRF kinematic waves

With waves

No waves

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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.

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ANY QUESTIONS ?

Thank you for listening

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For more information, please contact:

Peter Davies Renewable Energy Global Technology Leader Lloyd’s Register Group Services Ltd Denburn House, 25 Union Terrace Aberdeen, AB10 1NN T +44 (0)1224 267771 E [email protected] w www.lr.org/renewables