ESRU

Development and In-Sea Testing of a Single Point Mooring Supported Contra-rotating

Marine Turbine (CoRMaT)

Cameron JohnstoneDirector: Energy Systems Research Unit

University of Strathclyde, UKwww.esru.strath.ac.uk

Technology: Next Generation Tidal Turbine• The novel idea behind the contra-rotating turbine concept is to use

two closely spaced dissimilar rotors, moving in opposite directions

• This has several technical and cost advantages over single rotor designs:

– Increases relative shaft output speed– Increases the efficiency of energy capture– Eliminates complex blade pitch control– Reduces turbulent flow downstream of the rotors– Minimises reactive torque, thus promising a single point mooring

possibility– Increases the dynamic stability of the turbine in the tidal flow

• Electrical power take off is possible via direct drive of a contra-rotating generator, or by separate generators

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Concept Development

Hub

0

0.1

0.2

0.3

0.4

0.5

2 4 6 8 10 12

Tip speed ratio

Po

wer

co

eff

icie

nt

nominal plus2deg plus4deg

Poly. (nominal) Poly. (plus2deg) Poly. (plus4deg)

-20

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0

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0 20 40 60 80 100

Time (seconds)

Vgen (V)

Pitch (deg)

Roll (deg)

Phase 1: Tank Testing Phase 2: Rotor Testing Phase 3: System Testing

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Phase 1: 1/30th Scale Turbine Tow-Tank Tests

Hub

– Rotor performance:• Torque/ speed characteristics (power out).• Changes in blade pitch angle and rotor spacing.• Interaction between rotors.

– Structural/ mooring system• Dynamic loading due to reactive torque.

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1/30th Scale Turbine Tow Tank Testing

Hub

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1/30th Scale Turbine Performance ( )

0

0.1

0.2

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2 4 6 8 10 12

Tip speed ratio

Po

wer

co

eff

icie

nt

nominal plus2deg plus4deg

Poly. (nominal) Poly. (plus2deg) Poly. (plus4deg)

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Phase 2: 1/7th Scale 2.5m Blades – FEM DesignESRU

1/7th Scale CoRMaT alongside MV St Hilda

Miller Fifer 36’

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1/7th Scale CoRMaT Operating

Miller Fifer 36’

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1/7th Scale Turbine Performance

• Results are as predicted - within test series.

Rotor Dynamics Recorded

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Phase 3 Objectives (2008/ 09)

• To take the proven power capture, wake minimisation and torque cancelling properties of CoRMaT and integrate them into a standalone system that:

– Can easily be deployed, maintained, and recovered

– Generates electricity from a direct drive alternator

– Proves the proposed single-point mooring system

• Complete financial appraisal of scaling to a full scale system and development of the commercialisation plan.

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Phase 3 CRT-2 Schematic

Axial Flux Generator

Contra-rotating Blades

Rear Buoyancy

Front Buoyancy

To Tether

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Direct Drive, Open-to-sea Generator• Advantages:

– Ease of construction– Nacelle & casing leaks not an issue– Natural cooling– No complex sealing requirement– No large diameter seal friction

• Disadvantages:– Hydrodynamic effects of rotating

generator parts (negligible)– Marine growth potential

• Axial flux • Permanent magnet Ne-Fe-B• Rectified 3-phase output

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SpineRotors

Ne-Fe-B Magnets

Stator

Prime Mover 1

Shaft Prime Mover 2

Shaft

CoRMaT Test-tank Video ESRU

CoRMaT Mooring

• Single point tether from either a seabed gravity base or anchors:

– ease of installation and retrieval,

– low cost,– available proven

components,– flexible configuration, tuned

for differing depths, tidal climates and seabed composition.

– tracking of tidal diamond

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CoRMaT System Test Locations

1) Kyles of Bute

2) Sound of Islay

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CoRMaT System Test Location 1

Test SiteKyles of Bute

Site chosen as:– sheltered,– 2.6 knot tide,– easy access,– range of

shallow water depths (6 – 10m).

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CoRMaT System Testing

Installed miniCoRMaT system at slack water

Submerged Turbine

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Turbine Performance – Stability KoB

• Stability of device is good – improves under greater loading

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11.5

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0 500 1000 1500 2000 2500 3000 3500

Time (seconds)

Deg

rees

Turb Pitch (deg)

Turb Roll (deg)

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Sound of Islay (Visual Impact!)

Turbine buoy

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Site chosen as:– more

energetic,– 5.2 knot tide,– water depths

(12– 42 m).

FFT Analysis of CoRMaT pitch data showing dominant frequencies at Islay

Pitch Fn F1 F2 F3

Hz 0.597 1.792 3.885 8.167

Source Oversize nacelle

Fundamental rotor 1 speed

Combined rotor speed

Karman vortex

shedding

F2

FnF1 F3

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FFT Analysis of CoRMaT roll data showing dominant frequencies at Islay

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F3

F5 F6F4

F1

Roll F1 F4 F5 F6

Hz 1.859 9.362 35.657 47.742

Source Fundamental rotor 1 speed

5*F1 PMG stator non

uniformities (9*F2)

Blade- blade interactions

(12*F2)

CoRMaT Islay Deployment Video at ‘Slack Water !!!’

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CoRMaT: Next Phase, 2010 - University Spin-out Company- Marine Renewables Development

Deploy (X) x 250 kW turbines

Operate for 1 year and monitor deviceperformance and interactions

Option C chosen due to ‘off-the-shelf’ component availability

Direct drive 2 x 125 kW gen-sets per device

Development and Up-scaling of contra-rotating generator for next phase of deployment (Option D). Now being implemented

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G Gearbox GGearbox

A)

GDiff.

Gearbox

B)

G G

C)

D)G

Power Take-off Options

Conclusion• Contra-rotation can produce zero reactive torque, eliminate

the need for a gearbox and enable direct drive of a contra-rotating generator.

• Low cost single point mooring provides station keeping in different tidal stream conditions, without impacting on device performance.

• Simplified single point mooring system enables quick and easy deployment/ recovery.

• Considerably reduced system, installation and operational costs attained

• All IPR belongs solely to the University of Strathclyde with a sole license agreement to the University spinout company.

• UK (GB2005/161492) and International patents.

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