wind turbine rotor.docx

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1. PROJECT OVERVIEW

To implement the skills acquired in the previous semesters as prescribed in ME-67 design and fabrication project,

mechanical engineering, Anna university Chennai -

curriculum and to fulfil the above we focused in the area of

wind turbine. By getting basic ideas we have designed and

fabricated a 1kw wind turbine blade and calculated the

experimental results.



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2. INTRODUCTION

This report explains briefly about the design procedure and the

fabrication of a wind turbine blades. The design procedure has two

main steps.

I. CALCULATION OF THE POWER FROM THE WIND.

II. BLADE DESIGN

3. CALCULATION OF POWER FROM WIND.

Calculation of the power from the wind includes the calculationof the following parameters.

1. Diameter of the rotor.

2. Power from the rotor.

3. Mean power output.

4. Tip speed ratio (TSR).

5. Shaft speed.

i. DIAMETER OF THE ROTOR.

Diameter, D = (P/(C p x ρ/2 x π/4 x V3))

O.5(m)

Where,

ρ, density of air, (kg/m3) = 1.2 ( Temperature Dependent )

C p, Power co-efficient = C p< 0.6, say 0.4

V, Wind speed (m/s) = 9 m/s ( Rated Wind Speed )

P, power (Watts) = 1200 ( considering the

losses )

To find the diameter lets substitute the input parameters in the

equation, with the power rating of 1KW.

Diameter, D = ( 1200/(0.4 x (1.2/2) x (π/4) x (93))

0.5

= 2.95 m.

The rotor may be designed for diameter up to 3 meters.



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ii. POWER FROM THE ROTOR.

Power (in watts) is the rate of capture of energy, at any given

instant.

Power, P = Cp x ½ x ρ x A x V3

i.e.,

Power, P(watts) = Cp x ρ/2 x π/4 x D2

x V3

= 0.4 x (1.2/2) x π/4 x 2.952

x 93

= 1236.7 Watts.

If the windmill catches 40% of the raw power in the wind. Then

percentage caught is known as the 'power coefficient', Cp.

The raw power in the wind depends on the following.

1. The density of air.

2. The speed of the wind.

3. The size of the rotor.

Wind speed is critical, Stronger winds carry a greater mass of air

through the rotor per second and the kinetic energy per kilogram of

air depends on the square of its speed, so the power in the wind will

increase dramatically with wind speed.

iii. MEAN POWER OUTPUT.

Pm= 0.14 x D2

x Vm3

Where,

Pm = Mean Wind speed.

Vm = Mean Wind velocity.

Let us consider a mean wind velocity, Vm = 9 m/s.

Pm = 0.14 x (2.952) x (9

3)

= 0.14 x 2.952

x 93

= 888.17 watts on average.



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iv. TIP SPEED RATIO (TSR).

TIP SPEED RATIO (TSR) =(tip speed of blade)/(wind speed).

The tip speed ratio is a very important factor in the different formulas

of blade design.

Generally can be said, that a three bladed wind turbine use 5-7 as tip

speed ratios.

We can calculate the rotor tip speed ratio.

TSR = RPM x π x D/60/V

we calculate the rpm we can get with TSR = 7

RPM = 60 x V x TSR/(π x D)

= ( 60 x 9 x 7 )/( π x 2.95 )

= 407.8

All this is based on a 9 m/s wind speed. We must also consider the power and speed conditions at low winds like 4m/s.

P = Cp x ρ/2 x π/4 x D2

x 43

= 104.9 Watts.

Rpm = 60 x V x TSR/(π x D)

= 60 x 4 x 6/(3.14 x 2.95)

= 181.2 rpm

(So, the generator must produce some power at speeds under 200

rpm, if it is to work well in low winds.)

v. Shaft speed.

Rpm = 60 x V x TSR/(π x D) = 407.8 rpm

Shaft must be designed for up to 500 RPM.



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4. BLADE DESIGN.

The 'Blade Design' section suggests the shape of the blade at each

station. Say we use 5 stations along the blade length, at radius 'Rs' =0.29, 0.58, 0.87, 1.16, and 1.47 metre.

We choose,

B = 3 blades.

'CI' = 0.8.

'Alpha' = 4.Length = 1.47 m.

At each station we should find the setting angle 'Beta', and the

chord width 'Cw'

Blade setting angle, Beta = ATAN(D/3/Rs/TSR)-4

Chord width, Cw = 5.6 x L/(B x CI x Rs x TSR 2)

Drop = Cw x SIN(Beta)

Thickness = 0.15 x Cw (or 0.12 x Cw at the tip).

5. CALCULATIONS

i. For ‘Rs’ = 0.294

Beta = ATAN(2.95/3/0.294/7)-4

= 21.64˚

Cw = 5.6 x 1.47/(3 x 0.8 x0.294x 72)

= 0.210 m.

Drop = 0.210 x SIN(21.64˚)

= 0.077 m.

Thickness = 0.15 x 0.210

= 0.0315 m.



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ii. For ‘Rs’ = 0.588

Beta = ATAN(2.95/3/0.588/7)-4

= 9.43˚

Cw = 5.6 x 1.47/(3x0.8x0.588x72)

= 0.16 m.

Drop = 0.160xSIN(9.43˚)

= 0.026 m.

Thickness = 0.15x0.160

= 0.024 m.

iii. For ‘Rs’ = 0.882

Beta = ATAN(2.95/3/0.882/7)-4

= 5.04˚

Cw = 5.6x1.47/(3x0.8x0.882x72)

= 0.140 m.

Drop = 0.140xSIN(5.04˚)

= 0.012 m.


= 0.021 m.

iv. For ‘Rs’ = 1.176

Beta = ATAN(2.95/3/1.176/7)-4

= 2.81˚

Cw = 5.6x1.47/(3x0.8x1.176x7

2

)



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= 0.110 m.

Drop = 0.110xSIN(2.81˚)

= 0.005 m.


= 0.016 m.

v. For ‘Rs’ = 1.47

Beta = ATAN(2.95/3/1.47/7)-4

= 1.45˚

Cw = 5.6x1.47/(3x0.8x1.47x72)

= 0.09 m.

Drop = 0.09xSIN(1.45˚)

= 0.0022 m.


= 0.0135 m.

Naca 23015 profile was chosen



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6. FABRICATION OF THE BLADE

The blades are made from fibre glass. This fibre glass has great strength in

tension and compression. The various chemicals required are listed here.

1) Chemicals required

Resin Type ‘R 10-03’

This is a general purpose rigid orthopthalic

(FRP) polyester resin. It is relatively

inexpensive and is used for the majority of the

wind turbine blades.

Resin Type ‘Polymer 31-441’

This is called a ‘gel coat’ polyester resin. It is

100% isophthalic with Neo-Pentyl Glycol

(NPG). It is very hard wearing and is scratch

and chemical resistant. It is more expensive

than the other type of resin therefore its use is

limited to just the outer layers of the blade.

STYRENE MONOMER

This is mixed with the resin to reduce the

viscosity of the resin. This makes the resulting

mixture more workable and easier to ‘paint’

onto the fibre glass cloth.

HARDENER

Hardener is added to the resin mix to start the

solidification (or curing) process. The time taken

before the resin sets is controlled by the amount

of hardener and accelerator (cobalt) added. Once

the hardener is added to the resin it must be

worked quickly into the fibreglass as the resin

will solidify quickly.



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COBALT

Cobalt is an 'accelerator' that speeds up the

hardening process when added to the resin. This

can be used to help control the setting time of the

resin.

TONER

This only adds colour to the resin. It has no

structural properties. It is used to colour the

outer layers of resin, rather than paint the blades

afterwards. This can be obtained in manydifferent colours. Approx 5 to 10% by weight is

added to the resin mixture until the correct

colour is reached. Adding a greater amount than

this may inhibit the solidification process.

Adding toner makes the lay-up stage easier as

you can clearly see where the resin is, however

this makes the foam filling stage more difficult

as the blade is then opaque.

LOWILITE

This is a UV stabilizer and must be used on the

outer layers of resin. It helps to prevent material

degradation by sunlight. It is supplied in powder

form.

DURAWAX

This is a release agent. It is applied to the mould

before each ‘lay-up’ to ensure that the item

produced does not stick to the mould.

Sometimes a thin non-stick film is added to

moulds to avoid the part sticking – given the

complex curved shape of the moulds a wax

release agent was selected.



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FIBRE GLASS CHOPPED STRAND

FIBRE GLASS MAT (CSM)

The fibres within CSM are in random

orientation. This means that it has thesame strength in every direction. It is the

cheapest and easy to work with, as its

orientation does not matter. It used to

produce the moulds and a thin ‘veil’ of

100gsm is used to join the sides and

protect the leading edge.

WOVEN CLOTH FIBRE GLASS (WC)This consists of woven strands. It is

very strong in the direction of the

weave but is slightly more expensive

and harder to work with as the

orientation of the weave when the

piece is cut must be carefully chosen.

The cut weave has a tendency to

unravel when it is handled in a drystate.

THINNERS

Lacquer thinners are required to

remove excess resin and to clean up

any spills, paint brushes, pots and

tools. It is extremely flammable.

CAR BODY FILLER

A two-part car body filler is used to fill

small blemishes and gaps on the final

blades. Usually is supplied as a tin of

resin with a small tube of hardener. The resin is a thermal-set plastic.

The hardener, MEK peroxide, is a catalyst. The two components are

mixed in a proportion of approximately 1% to 3% hardener to resin.

Use a good quality brand.



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EXPANDING FOAM

A two-part expanding polyurethane low density foam is used to fill

the air gaps within the blade. The foam is initially two liquids which

must be mixed in a ratio of 1:1. This will then expand to 25 times its

initial volume. Such foam is used in boat building and construction.

This foam may not be required and the structure can be left empty but

it significantly improves the rigidity and strength of the blade.

2) BLADE MANUFACTURE

The blade is comprised of two blade halves, the windward half and

the backward half. Each blade half is built up from 16 layers of fibre

glass mat. Woven cloth (WC) is used for additional strength in the

direction the forces act on the blades.

Materials required:

For one blade:

The general process is as follows:

1. Preparation: Cut the layers of fibreglass WC. 16 layers are used in

each half.

2.Preparation:Prepare batches of resin mixture and the corresponding

batches of hardener.

4. Preparation: Wax the mould to ensure easy release.



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5. Procedure: Fill the moulds with a layer of resin, then a layer of

fibreglass WC until all 16 layer have been placed. The weave of

the WC must be rotated by 45 degrees between each layer.

6. Procedure: Leave to dry.

3) BLADE JOINING

When set, the two halves of the blade need to be joined to form a

single unit. To do this they need to be accurately cut so that the two

pieces fit together. The join should be made with minimal impact on

the blades aerodynamic shape.

Also additional strength and rigidity is added to the blade through theuse of a ‘stringer’ from the root to the tip. A wooden core is inserted

at the root. This is so the screws used to hold the blades to the wind

turbine have something to ‘bite’ into. It also stops the blade root

collapsing when the front blade assembly is bolted onto the generator

on the wind turbine.

4) BLADE TRIMMING

Firstly the excess (over lap from the mould) must be cut off. This was

done with a circular cutting saw. A jigsaw or a mini-cutter could also

be used. A line should be visible at the edge of the part, distinctly

showing the smooth section from the mould and the excess overlap.

Then grind down the inside edges at approximately 45 degrees. This

is to allow the two blade halves to fit just inside each other to make a

full blade. The two halves can be placed together for comparison to

check they fit well. This can be a long process and usually requires afew attempts (additional grinding) until the two halves fit perfectly.

5) BLADE ROOT

A steel core is required at the blade root - where the blade is screwed

to the blade hub. The blade root should fit snugly in the root of the

blade and go far enough down the blade so that all the screws will bite

into the steel core.



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6) BLADE FINISHING

The blade halves have been stuck together and filled with foam, the

Last stage is the blade finishing. This involves filling any gaps on the

blade edges, adding a thin ‘veil’ of fibre glass to the leading edge,sanding down any imperfections and painting.

Fill any gaps along the leading edge with good quality filler, such as

car body filler. Leave this to dry.

Sand the blade along the leading edge and ensure that the surface is

smooth. Add a narrow strip of CSM fibreglass to the leading edge.

Two layers should be applied. This is to help hold together the two blade halves and also to add an additional layer to help protect the

leading edge.

Sand the blade to ensure that all the surfaces are smooth, especially

along the leading edge. The edge of the trailing edge should be thin,

approximately 1mm or less width. This will be the final sanding

process.



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7. THE FINAL BLADES



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8. CONCLUSION

Thus a wind turbine blade was successfully designed and fabricated,

for the given power and other requirements. The blade is designed toultimate perfection considering the loads and stresses acting on it.

The profile chosen for the blade was also analysed for its

aerodynamic properties and considered as best for the implementation

in the wind turbine.

wind turbine rotor.docx

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