peter davies & morten boegild - tidal turbine array modelling, influence of waves on turbine...
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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
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
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 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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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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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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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 peter.davies@lr.org w www.lr.org/renewables
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