wind turbine blades - an overview

BladesDesign, Materials and manufacture

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Wind Turbine Blades – An Overview3

Naming and definitions

Leading edge

Trailing edge

root

Tip

Leeward

Torsion/pitch

Flap direction

Edge direction

Profile

chord

Pitch axis/sweep angle

Windward

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Blade Requirements

What do we need from our Blades?• Low weight

– Reduce loads on rest of turbine– Easier to transport and handle

• Stiff– Tower Strike is a ‘design

constraint’– Need to maintain aerodynamic

shape• Strength and Durability

– Avoid Material Failure (extreme loads and fatigue), buckling, performance degradation due to erosion etc.

• Aerodynamic design• Easy to manufacture• Low price

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Loads on the Blade

Rotational speed

Lift

Drag

Bending force

Wind speed

Relative wind speed

Effective driving force

Centre line

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Loads on the Blade

Design Loads are split into 2 sets: • Edgewise • Flapwise Need to consider • Extreme Cases• Fatigue Loads

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Loads on the Blade• Load magnitudes are high.

• For the extreme forward flapwise case it is the same as hanging 2 empty double decker london buses from the tip of the blade!!

• Under this load the blade deflects by about 10m at the tip.

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Structural Concepts

How do we get a light, stiff and strong blade that can withstand the loads for 20 years ?

Efficient arrangement of the best materials.

Pre-Preg Blade

Wood Carbon Blade

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Materials

• Glass fibre (Unidirectional, or woven)

• Carbon fibre (Unidirectional layers or prefabricated rods

• Epoxy • PUR-glue• High density PVC-foam• Wood (balsa, plywood)• Steel and copper

Manufacture of PrePreg Blades

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Sub process Precutting of prepreg

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Supporting carbon spar concept• The supporting spar with a

rectangular section • The airfoil shells with sandwich

construction at the rear

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Prepreg

• PREimPREGnated glass or carbon fibres

• Fibres impregnated with epoxy resin and hardener

• Prepreg is tacky and easy mount• Vacuum is used to remove air and

heat start the hardening process

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Manufacture

Root joint

Main spar Shells Finish

Tip spar Precuttingprepreg

Painting

Main process

Sub process

Start End

Process flow prepreg blade production

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Sub process Tip spar Lay-up on tip spar

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Sub process Curing of tip spar

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Main process Main spar Putting on root joint

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Main process Putting on tip spar

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Main process Lay-up on main spar

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Main process Curing of main spar

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Main process Shells Layout of coat

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Main process Lay-up of prepreg

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Main process Lay-up of PVC

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Main process Vacuum on shells

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Main process Curing of shells / close mould

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Main process Remove support materials

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Main process Layout glue

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Main process Putting main spar into the shells

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Main process Open the mould after curing of glue

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Main process Moving the blade after de-moulding

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Main process Finish Grinding / repair of edges

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Main process Grinding with flatter grinding machine

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Main process Painting of blade

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Blade WeightsBlade length

Weight (approx.)

23 meter 1300 Kg

25 meter 1800 Kg

32 meter 3600 Kg

39 meter 6500 Kg

44 meter 6300 Kg

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Wood carbon concept• ‘Sandwich’ Construction to provide extra flexural stiffness• Carbon pultrusions provide extra ‘global’ stiffness• Glass along TE provides stiffness for edgewise loads.

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Wood Carbon ManufactureLay Materials into Blade

halves (Leeward/Windward

Vacuum Assisted Resin infusion

Cure Cycle

‘Debagging’

Join Up

Breakout

Finishing

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