Contact Pressure Validation of Steam Turbine Casing for Static Loading Condition
Wind Turbine Report Final
1. I
Engineering Design and Sustainability
Design and Manufacture of
Wind Turbine Blades
Group A
Richard Sims 3200692
James Goddings 3131147
Mihail Kirov 272818
Daniel Dormer 2929611
Jamie Haslam 3222582
Josh Wilkinson 3129340
Adrian Elliot 3036931
Complied: 27th
April 2015
Submission Date: 15th
May 2015
(EEC_5_977_1415)
Marker: Dr. N. Zlatov
Abstract
This report describes the procedure undertaken to design, develop, manufacture and test three
blades for a wind turbine. The product design specification is initially presented, identifying the key
design objects. This is then followed by a succinct review of design theory and calculations utilised to
validate the design. A cost for the system is presented, allowing commercial viability to be
determined. Subsequently, the manufacturing process is described along with an evaluation of the
test rig. The test methodology and results are then presented, followed by a critical analysis of the
data collected.
2. Page 1 of 31
Table of Contents
Abstract...................................................................................................................................................0
1. Aim......................................................................................................................................................3
2 Introduction .........................................................................................................................................3
3. Project Plan.........................................................................................................................................3
4. Project Design Specification................................................................................................................4
5. Design..................................................................................................................................................4
5.1 Test Rig Evaluation........................................................................................................................4
5.1.0. Wind Speed Evaluation.........................................................................................................4
5.1.1 Generator Considerations......................................................................................................5
5.2. Theory and Design Calculations...................................................................................................5
5.2.0. Aerofoil Design......................................................................................................................6
5.2.1. Betz’s Law..............................................................................................................................6
5.2.2. Aerofoil profile......................................................................................................................7
5.3.1. Blue-Foam.............................................................................................................................9
5.3.2. MDF.......................................................................................................................................9
5.3.3. Fibre Glass.............................................................................................................................9
5.3.4. Aluminium...........................................................................................................................10
5.3.5. Design Scoring.....................................................................................................................10
5.4. Design Model .............................................................................................................................11
5.5. Costing .......................................................................................................................................11
6. Execution...........................................................................................................................................12
6.1 Part Manufacture........................................................................................................................12
6.2 Part Assembly .............................................................................................................................13
6.3 Inspection of Parts ......................................................................................................................13
7. Electrical System Optimisation .........................................................................................................13
8. Wind Turbine Testing........................................................................................................................15
9. Discussion..........................................................................................................................................15
10. Conclusion.......................................................................................................................................16
References ............................................................................................................................................17
APPENDIX A – Project Planning...............................................................................................................1
APPENDIX B – Wind Speed Distribution From Centre Of Hub................................................................1
3. Page 2 of 31
APPENDIX C – Shimano DH-3N71 Generator Data .................................................................................2
APPENDIX D – NACA/NASA 4412 Aerofoil Data......................................................................................4
APPENDIX E – Calculated Data................................................................................................................5
Appendix F: Forces, Bending Moments and Deflection..........................................................................1
Appendix G: Cost breakdown .................................................................................................................1
APPENDIX H – Inspection Reports ..........................................................................................................1
APPENDIX I – Electrical Optimalisation...................................................................................................2
APPENDIX J– Wind Turbine Testing ........................................................................................................4
4. 3
1. Aim
The aim of this report is to detail the process undertaken to design, develop, manufacture and test
three blades for a wind turbine. The purpose of the design is to extract maximum electrical power
out of the rig by optimising the turbine blade design. Particular emphasis is placed upon the
sustainability aspects throughout the whole of the project.
2 Introduction
Wind turbine blades are shaped to generate the maximum power from the wind at the minimum
cost. Primarily the design is driven by the aerodynamic requirements, but this objective should be
met by well satisfying mechanical strength criteria and economical aspects. In particular, the blade
tends to be thicker than the aerodynamic optimum close to the root, where the stresses due to
bending are greatest.
The blade design process starts with a “best guess” compromise between aerodynamic and
structural efficiency. The choice of materials and manufacturing process will also have an influence
on how thin (hence aerodynamically ideal) the blade can be built. The chosen aerodynamic shape
gives rise to loads generated by lift, which are fed into the structure of the blade. Varying wind
speeds and directions give rise to uneven loading on the blades thus inducing additional forces to
the structure.
A detailed description of designing, planning, manufacturing and testing of a set of three wind
turbine blades is provided in the main body of this report.
3. Project Plan
Project planning is a complicated process and its implementation goes through many iterations. As
pointed out by Newton (2009) project plans are fundamental to the way projects are managed as
they determine the cost, timescales and risk levels (Newton, 2009).
Appropriate planning enables cost, time, resources and progress to be established efficiently and
corrective actions to be undertaken, if deemed necessary.
A Master Plan having three milestones was prepared and agreed by all part-time students as a mean
of controlling and monitoring the progress of this project. A Work Breakdown Structure (WBS) was
used to prepare the project plan and define scope, objectives and deliverables for each work
element in the project. This can be found in Appendix A.
Gantt charts were developed from the WBS. As defined by Larson & Gray (2011) “The Gantt chart is
a visual flow diagram of the sequence, interrelationships, and dependencies of all the activities that
must be accomplished to complete the project” (Larson & Gray, 2011). Gantt charts provide the
project schedule by identifying dependencies, sequencing, and timing of activities, which the WBS is
not designed to do.
The Gantt charts for this project as well as the network diagram used for the Critical Path analysis
can be found in Appendix A.
5. Page 4 of 31
4. Project Design Specification
Key Parameters for Blade design.
Number of Blades: Three to suit test rig.
Design Speed: 400 rpm to utilise maximum rated output of dynamo/generator.
Materials: Constructed from sustainable materials.
Method of construction: Simple, Low Cost, Repeatable, CAD / CAM precision, Low Starting
Inertia.
Set Dimensions: 510mm x 150mm x min 25 (mm)
5. Design
5.1 Test Rig Evaluation
Before the turbine blade design could begin it was important to analyse the supplied test rig to
calculate the initial parameters. These include the
optimum operating speed of the generator, the
expected oncoming wind speed at the blades and the
dimensions of the hub to mount the blades to.
5.1.0. Wind Speed Evaluation
To calculate the wind speed expected at the turbine
blades, an investigation of the airflow profile and
distribution was carried out so the design of the blades
could be optimised to these conditions. An anemometer
was used to take measurements of the wind speed at
different distances from the centre of the hub as can be
seen in figure 1. The different positions at which
measurements were taken are represented by the black
dots. Tabulated results are shown in appendix B.
Figure 2 - Wind Speed Trend
The results from figure 2 above show that there is a near linear relationship between the wind speed
and the distance from the turbine centre. It was established that wind speed is inversely
proportional to the distance from the centre of its projection, a result which was expected. The
design of the blades needs to incorporate this variation in wind speed over the blade length.
Trend Line equation
y = -22.925x + 11.544
0.00
5.00
10.00
15.00
0 0.1 0.2 0.3 0.4 0.5 0.6
Windspeed(m/s)
Distance from turbine centre (m)
Wind speed vs distance from turbine centre
Figure 1- Wind Speed Measurements
6. Page 5 of 31
5.1.1 Generator Considerations
The driven generator which is used to produce electrical power was a key consideration in the
design process. Electrical generators are designed to deliver a specific output under intended
conditions.
The generator used for this investigation is a Shimano DH-3N71 dynamo hub designed for powering
bicycle lights. As per the datasheet in appendix C, it is an Induction AC generator specified to provide
3W at 6V, when built on a wheel measuring 700mm in diameter, of a bicycle travelling at 15km/h.
Tests performed by Andreas Oehler (Oehler, A., 2012) shown in figure 3 on various bicycle dynamo
hubs, including the successor to the DH-3N71, the DH-3N80, which contains the same generator
components with improved bearings and a lighter axle. These readings were made while attached to
a 24Ω resistor intended to simulate 2 lights in series. The voltage remained unregulated, allowing
the power output of the DH-3N80 to climb to 12.5W at 50km/h.
50km/h is a high speed for a bicycle, so it
would be an acceptable assumption that
this would be approaching the upper
design limit of the hub. This applies from
a mechanical standpoint, with regards to
bearing limitations, and an electrical one,
as AC generators become increasingly less
efficient as they exceed their designed
rotational velocity and internal resistance
and hysteresis increase dissipating energy
as heat. This upper limit is seen as a
practical starting point of design of the
turbine blades, and translates to
rotational velocity according to the
following calculations:
𝑣 𝑏𝑖𝑐𝑦𝑐𝑙𝑒 = 50 [
𝑘𝑚
ℎ
] = 833.3 [
𝑚
𝑚𝑖𝑛
] = 13.9 [
𝑚
𝑠
] Equation 2.3.i
𝑑 𝑤ℎ𝑒𝑒𝑙 = 700[𝑚𝑚] = 0.7[𝑚]
Equation 2.3.ii
𝑣 𝑏𝑖𝑐𝑦𝑐𝑙𝑒
𝜋𝑑 𝑤ℎ𝑒𝑒𝑙
=
833.3
𝜋 × 0.7
= 379[𝑟𝑝𝑚] ≈ 400[𝑟𝑝𝑚]
Equation 2.3.iii
From this research the optimal operating speed of the generator was found to be 400rpm in which
the turbine blades will be designed around.
5.2. Theory and Design Calculations
The fan is intended to simulate the presence of wind by producing a constant flow of air. However it
is not a true representation of how the wind turbine would perform in reality and therefore the
results will be an approximation. True wind would approach the turbine with uniform velocity
distribution across the swept area (ignoring ground effects). As per the wind speed evaluation the
fan on the test rig delivers a non-uniform, locally concentrated velocity distribution.
Figure 3 - Power Generated Versus Speed of Bicycle for Various
Bicycle Hub Generators (Oehler, 2012)
7. Page 6 of 31
It is therefore apparent that the optimum aerofoil design for achieving the maximum power in the
functional assessment of this project may not be a true representation of a real-world wind turbine
aerofoil. However, the development process is still very similar process to that of a real turbine.
5.2.0. Aerofoil Design
A combination and adaptation of approaches suggested by Hugh Piggott in Windpower Workshop –
Building Your Own Wind Turbine, and Barney Townsend in his Lecture Notes Aerofoil Selection and
Wind Turbine Design (see Appendix D) were used for the Aerofoil design.
Firstly a blade length of 510mm from the blade mounting bracket to the tip of the blade was decided
upon as a suitable; this was selected based on the wind speed distribution from the test rig fan (see
Section 5.1), allowing full use of the available wind, and coincided with being the maximum
permissible blade length. This resulted in making the overall length from the hub centre to the blade
tip 580mm,
Using Ragheb, M, (2014) Formulae a tip speed ratio was calculated based on the optimum generator
speed of 400rpm and a maximum wind speed of 10m/s (see Section 2.3.1) as follows:
𝑇𝑖𝑝 𝑆𝑝𝑒𝑒𝑑 𝑅𝑎𝑡𝑖𝑜 (𝜆) =
𝜔 𝑏𝑙𝑎𝑑𝑒 × 𝑟𝑏𝑙𝑎𝑑𝑒
𝑣 𝑤𝑖𝑛𝑑 Equation 2.3.iv
𝑊ℎ𝑒𝑟𝑒:
𝜔 = 𝐴𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 (𝑟𝑎𝑑𝑠/𝑠𝑒𝑐)
𝑟 = 𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑏𝑙𝑎𝑑𝑒 (𝑚𝑒𝑡𝑒𝑟𝑠)
𝑣 = 𝑊𝑖𝑛𝑑 𝑠𝑝𝑒𝑒𝑑 (𝑚/𝑠𝑒𝑐)
Convert rpm to angular velocity = 𝜔 =
𝑟𝑝𝑚×2𝜋
60 Equation 2.3.v
∴ 𝜆 =
𝑟𝑝𝑚 × 2𝜋𝑟
60 × 𝑣 Equation 2.3.vi
𝜆 =
400[𝑟𝑝𝑚] × 2𝜋 × 0.58[𝑚]
60 [
𝑠
𝑚𝑖𝑛
] × 10 [
𝑚
𝑠
]
= 2.43 Equation 2.3.vii
This wind tip speed ratio is lower that the “optimal wind tip speed ratio is reported as 7” as reported
by Ragheb, M, (2014). Increasing this ratio would speed up the generator and thus it will run above
its optimal speed.
5.2.1. Betz’s Law
Betz’s Law states that the ratio of the
velocities of the wind incident on the turbine
and the wind behind the turbine is the
determining factor of how much energy can
be extracted from the wind, leading to a
maximum efficiency of any wind turbine of
59.3% at a velocity ratio of 1/3 downstream
to upstream (see Figure 4).
Figure 4 - Graph Illustrating Betz’s Limit.
(www.wind-power-program.com, 2015)
8. Page 7 of 31
As a turbine extracts energy from the wind, it slows the wind and accelerates the turbine blades; this
creates a pressure drop immediately downstream of the turbine in accordance with Bernoulli’s
principle. The energy extracted causes the blades to spin faster, however this increases effective
area of the turbine blades as a function of time, thus increasing the drag force as a function of time
see Equation 2.3.ix. An increased pressure zone in front of the turbine is created, however the
airflow is not contained, and therefore the pressure can dissipate laterally away from the blade.
𝑑𝐹𝐷
𝑑𝑡
=
1
2
𝜌𝑢2
𝐶 𝐷
𝑑𝐴
𝑑𝑡 Equation 2.3.ix
If the effective area of the turbine blades as a function of time increases beyond a certain point, the
braking effect on the wind from the drag of the blades becomes so great that the airflow deviates
around the turbine, bypassing the blades and creating an energy sapping vortex behind the turbine
as the air rushes to fill the decreased pressure area
immediately behind it. This slows the turbine,
resulting in a maximum rotational velocity that any
turbine can achieve dependent on the number of
blades and the incident drag effective surface area.
Figure 5 shows a chart of theoretically derived,
optimal power coefficients that turbines of differing
blade numbers can produce. This indicates that a 3
blade turbine would be most efficient at a tip speed
ratio of 6-8.
5.2.2. Aerofoil profile
A suitable Aerofoil profile was selected based on research and studying the NACA/NASA aerofoil
data available on Airfoil Tools website (http://airfoiltools.com/ ). A 4412 profile was decided upon
given its favourable Coefficient of Lift to Coefficient of Drag relationship, exhibited over relatively
wide range of Angle of Attack (see Appendix D).
The blade was divided into sections or stations along its length and the following calculations
performed for each station separated by 35mm giving 13 stations:
Firstly the wind velocity generated by the fan at each station perpendicular to the plane of the
turbine was calculated using testing data from the Test Rig Evaluation:
𝑣 𝑟 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 = −22.9𝑟𝑠𝑡𝑎𝑡𝑖𝑜𝑛 + 11.5
Equation 2.3.x
Then the wind velocity induced by the blades rotating at 400rpm in the plane of turbine was
calculated:
𝑣 𝜃 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 = 2𝜋𝑟 ×
400𝑟𝑝𝑚
60 [
𝑠
𝑚𝑖𝑛
] Equation 2.3.xi
Figure 5 - Graph of Tip Speed Ratio against Rotor Power
Coefficient Produced, (Predescu et Al. 2009)
9. Page 8 of 31
Then the resultant vector wind velocity and angle were
calculated using trigonometry, see Figure 6.
𝑢 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 = √𝑣 𝑟 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
2
× 𝑣 𝜃 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
2 Equation
2.3.xii
𝛼 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 = 𝑡𝑎𝑛−1
𝑣 𝑟 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
𝑣 𝜃 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
Equation
2.3.xiii
A method proposed was then used whereby a uniform
chord length for the aerofoil was adopted along its length,
and the Lift Force generated at each station calculated (see Equation 2.3.xviii). Due to the Plan
Viewed Surface Area being a contributory factor to the Lift Force generated by an Aerofoil, the
maximum chord length permitted by the brief of 150mm (0.15m) was used.
𝑅𝑒𝑦𝑛𝑜𝑙𝑑𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 (𝑅𝑒) =
𝜌 𝑎𝑖𝑟 𝑣 𝑤𝑖𝑛𝑑 𝑙 𝑐ℎ𝑜𝑟𝑑
𝜇 𝑎𝑖𝑟 Equation 2.3.xiv
𝑅𝑒 =
1.2 [
𝑘𝑔
𝑚3] {@20°𝐶} × 10 [
𝑚
𝑠
] × 0.15[𝑚]
1.51 × 10−5 [
𝑚2
𝑠
] {@20°𝐶}
= 119205
Equation 2.3.xv
𝐴𝑝𝑝𝑒𝑛𝑑𝑖𝑥 𝐷: 𝐴𝑒𝑟𝑜𝑓𝑜𝑖𝑙 4412,
𝑅𝑒 = 100,000 𝑎𝑛𝑑 𝐴𝑂𝐴 = 5° → 𝐶𝐿 = 1.0, 𝐶 𝐷 = 0.02 Equation 2.3.xvi
𝐿𝑖𝑓𝑡 𝐹𝑜𝑟𝑐𝑒 𝐹𝐿 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 =
1
2
𝐶𝐿 𝜌𝑢 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
2
𝐴 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 Equation 2.3.xvii
𝐹𝐿 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 =
1
2
× 1 × 1.2 [
𝑘𝑔
𝑚3
] × 𝑢 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
2
[
𝑚
𝑠
] × (0.035 × 0.15)[𝑚2
] Equation 2.3.xviii
To balance the lift forces along the blade, in order to equalise stresses along its length and maximise
efficiency, a number of methods could have been implemented as follows:
Altering the angle of attack of each station relative to the resultant wind to change the
coefficient of lift, and therefore lift force.
Altering the blade profile at each station to change the coefficient of lift, and therefore lift
force.
Altering the chord length, and therefore surface area, to change the lift force.
The third of these methods was chosen; because the stations were all the same width it was only
necessary to adjust chord length at each station in order to effect a proportional change in lift force.
This was done by taking the lift force at each station, subtracting the lowest lift force value, and
dividing 150mm (0.15m) by this value to generate the new chord length, thereby balancing the lift
forces see Equation 2.3.xvii. Tables in Appendix E show the resulting data from these calculations at
each of the 13 stations.
𝑙 𝑐ℎ𝑜𝑟𝑑 𝑎𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑠𝑡𝑎𝑡𝑖𝑜𝑛 =
𝐹𝐿 𝑚𝑖𝑛
𝐹𝐿 𝑠𝑡𝑎𝑡𝑖𝑜𝑛
× 150𝑚𝑚
Equation 2.3.xix
It was realised that the two final smallest profile elements were not practical for construction so the
last three elements were to be identical in chord length as the additional lift would be minimal.
Figure 6 - Resultant vector wind on turbine blades
10. Page 9 of 31
5.3. Product Designs
There are a variety of ways to accomplish the task of constructing wind turbine blades and there are
numerous materials which can be used. The most readily obtainable materials are, Blue-Foam,
Aluminium, MDF (Medium Density Fibreboard) and Fibre Glass. The task to create 3 turbine blades
using sustainable materials which ideally are not too heavy or too light and can be designed and
assembled within a relatively short timeframe. Below are the materials and design concepts which
were chosen for the task with their characteristics and a brief description of their pros and cons.
5.3.1. Blue-Foam
Blue extruded polystyrene foam is light weight foam which is easily carved and shaped. It has a high
compressive strength due to its rigid cell makeup and high water resistivity.
The design for the hollow PVC wing would consist of shaping the solid blue foam block into a mould,
then vacuum forming a PVC outer shell around it.
Cons
Production of the foam is not fully sustainable as it is manufactured from crude oil.
Harmful to humans if the dust is inhaled a possible carcinogen.
Low tensile strength
Pros
It is very light.
Easy to carve and shape.
High compressive strength
5.3.2. MDF
MDF or (Medium Density Fibreboard) is made from wood shavings mixed with wax and resin which
is then heated and compressed to create a dense, easy to shape and light wood substitute. The MDF
design would consist of either a solid block shaped by hand or a ribbed wing of 2.5 mm thick sections.
Cons
Loses rigidly if exposed to water.
If designed as a solid blade it would heavy, which can increase the initial inertia.
Pros
Sustainable material, made from previously recycled wood shavings.
Not too light as to slow to a stop if an electrical resistance is applied.
Easy to work with, can be cut by laser.
5.3.3. Fibre Glass
Fibre reinforced plastic or fibre glass is a strong and light weight material made from a composite of
plastics, a woven glass fibre mat like weave which can be used for example to reinforce plastic
resins. The idea of using fibre glass would be in a typical wing shape, the method would be similar to
the blue foam method needing a solid base. However then it would need several layers of resin and
fibre glass. Due to timescales and the hazardous nature it was decided not to go any further in the
design.
Cons
Difficult to work with
Damages the environment as made from toxic resins
Harmful to health if inhaled and possible carcinogenic
Pros
Strong and lightweight
Water resistant
11. Page 10 of 31
5.3.4. Aluminium
Aluminium is a strong and low density light weight metal with excellent malleability and easy to
machine. The Aluminium design would be a curved sheet design as a solid design would be
heavy and very time consuming. Two curved sheet designs were looked at however one was
better suited to a vertical wind turbine.
Cons
Energy hungry in its production
Relatively expensive compared to the other materials.
Time consuming to build with.
Pros
Very strong and lightweight for a metal.
Rust resistant.
Easy to recycle.
5.3.5. Design Scoring
To find a viable choice of build and material, an implementation checklist was created. The material
and build attributes were scored between 1 and 10 to define the strengths and weaknesses of their
materials and design.
Materials Sustainability Workability Material
Weight
Machining
Accuracy
Timescales Material
strength
Total
Aluminium 7 2 6 8 -9 9 23
MDF solid 7 8 6 5 -7 5 24
Fibreglass 5 2 7 2 -9 8 17
Vacuum
Formed PVC
5 7 5 6 -5 3 21
2.5mmm MDF
Ribbed 7 8 6 9 -3 5 32
Table 1 - Results from the Implementation Checklist
The final result gave favour to the ribbed wing build, this led to two further options being available,
the first was to model the wing in CAD and import it to 123D Make, by Autodesk. This creates a
skeleton in a lattice style of the wing. The MDF could then be laser cut and joined together like a 3D
jigsaw and could then be wrapped in a light material. The 2nd
option was to create the NACA profiles
of different sizes in CAD, then convert the file to manufacture them using the laser cutter from
2.5mm MDF. They would then be joined via a strong spine with a solid.
Due to time restrictions it was decided to use the latter rib with metal spine method. As little was
known of the Autodesk software and it would be advantageous to be able to alter the aerofoil
section angles to optimise the design.
12. Page 11 of 31
No
Required
Resources
Cost
per blade
(£)
Total
Cost
(£)
for 3
blades
1 Materials 11.30 33.90
2 Labour 23.50 70.50
34.80£ 104.40£Total
Table 2: Summary of materials and labour costs
y = 0.3255x0.2608
R² = 0.9999
0
0.1
0.2
0.3
0.4
0.5
0.6
0.0 1.0 2.0 3.0 4.0 5.0 6.0
Distancefrom,BladeRoot(m)
Deflection (mm)
Deflection along blade length
5.4. Design Model
The process of 3D virtual prototyping
required the complex review of drag and lift
coefficients, mechanical loads based upon
permissible and realistic performance goals
set out in the PDS.
A final design of the blades was generated in
Autodesk Inventor. The virtual design was
then put through FEA to ensure that the
design is capable of withstanding the
expected loads, in addition to the mechanical
and aerodynamic loads.
Deflection calculations were
carried out to identify the
stiffness of the design as a result
of the stresses on the blade
surface this can be seen in figure
8 opposite. Full calculations are in
appendix F. The maximum
deflection seen is 6mm at the tip
of the blade this is acceptable
considering the materials used
and the minimal stress it
generates over the length of the
blade.
From both of these stress analysis methods it can be seen the initial design of the blade is suitable
for operation and can be progressed to manufacture.
5.5. Costing
For the purpose of this project only direct costs for labour and material have been taken into
account. Overhead costs, marketing, transportation etc. were excluded from it. Table 1 provides a
summary of materials and labour costs for the project.
Notes:
1. Electrical parts not included
2. Workshop machinery and depreciation of
assets not included
3. Overheads, marketing, transportation etc.
cost not included
Table 2 - Summary of materials and labour cost
Figure 7 - Blade FEA
Figure 8 - Blade Deflection
13. Page 12 of 31
A detailed breakdown of materials and labour costs required for manufacturing a set of three wind
turbine blades can be found in Appendix G.
Cost, time, and budget estimates are the lifeline for control of the project’s progress; they serve as
the standard for comparison of actual and plan throughout the life of the project.
In summary, planning establishes the way projects are managed as they determine the cost,
timescales, required resources and risk levels. The WBS is used to decomposition the projects into
more manageable chunks of work and assign ownership for tasks. Gantt charts are usually the most
popular form of plan presentation. Alternatively box plans or network diagrams could be used. More
detailed plans are often perceived to be better plans.
6. Execution
6.1 Part Manufacture
Manufacturing initially began with cutting
the rib profiles on the universal laser
cutter. This involved arranging the
required profiles onto the supplied LSBU
.dwt template laid out in a way as to
minimise the wastage. With a 3mm sheet
of MDF placed in the machine the
populated template was sent to cutter for
manufacture. Once these profiles had
been cut they were gently pressed out by
hand.
Manufacture of the 3x blade bases began from 25mm MDF
cut to 150 x 75mm. The 150mm aerofoil shape was dawn on
the upper and lower edges, with the band saw these
markings were followed and an accurate smooth finish
gained using the linisher. The 5x 5mm holes drilled on the
pillar drill and the upper M6 hole drilled and tapped on the
mill.
3 lengths of M6 stainless steel studding cut to 260mm and 3
lengths of M3 stainless steel studding cut to 190mm, ends de-
burred.
To join the studs together an adaptor was manufactured on the
lathe 8mm in diameter and 15mm in length, drilled and tapped M3
one end and M6 the other.
Figure 7- Laser cut profiles
Figure 8 - Blade base
Figure 9 - M3 / M6 stud adaptor
14. Page 13 of 31
6.2 Part Assembly
The rib sections were attached to
the studding with a nut either side,
each rib was spaced at 35mm pitch
from the end of the studding. The
blade base was screwed on to give
a distance of 35mm to the first rib
and locked in place with an M6 nut.
The nuts tightened once the ribs
had been aligned parallel.
A jig was manufactured to assist twisting each rib section. The blade
base was mounted to a 90° angle plate, the jig was placed behind
each rib and the rib twisted to the required marking on the jig.
Once the ribs had been twisted on all three blades the aluminium
foil tape could be applied. Starting from the rear of the aerofoils the
tape was laid down the blade pressing the tape onto each rib
section. The final layer of tape was curled to shape over the leading
radius of the aerofoils before applying to give a smooth finish.
6.3 Inspection of Parts
To reduce the vibrations generated by the turbine the three blades required balancing. Once all
three blades had been manufactured, each blade was weighed. Weight was removed from the
heavier blades by drilling holes into the MDF blade bases; minor weight was added by applying small
pieces of aluminium foil tape until each blade weighed within 0.02g of each other.
After completion of each individual component, checks were carried out to ensure they were
manufactured as per the drawings, see appendix H for inspection reports. Inspection at such an early
stage ensured each part was correctly manufactured before adding it to the final part preventing
problems later down the build stage.4. Testing
7. Electrical System Optimisation
The system was initially tested a 3W 6V lamp as the load placed on the system. This allowed basic
demonstration of the system. However, this limited the amount in which the load could be varied
therefore, the optimal load could not be found. It was also found from the preliminary testing that
the system provided power in excess of the lamps rated operating conditions, resulting in several
lamps being blown. This corresponds to the warnings from the dynamo datasheet (appendix C); this
hub dynamo does not have overvoltage protection inside the hub itself Technical Service
Information DH-3N71 (2006). The rotational shaft speed (RPM) controls the dynamo or alternator’s
output voltage (Holden ,2011) therefore suggesting that the system was rotating faster than the
dynamo was designed for.
Figure 11 - Blade Pitching
Figure 10 - Blade Twisting
15. Page 14 of 31
The load was changed from the lamp to a large variable resistor selected with appropriate power
handling capability. Changing the load yielded two significant advantages, firstly, it meant that the
system load could easily be varied to find optimum load. Secondly, as the load was purely resistive,
this simplified electrical calculations as Ohm’s law could be applied. The familiar Ohm’s law triangle
used for DC circuits can only be used at AC if the load is purely resistive (Collinson (No Date)).
A basic schematic of the electrical system can be seen below in figure 12.
With the blades set to an angle of attack of 28.5° the resistive load was varied to obtain the
maximum calculated power. As only voltage and current could be measured, power and resistance
were calculated using equations 7.i. & 7.ii.
Power was calculated by:
𝑃 = 𝑉 ∗ 𝐼
Equation 7.i. [Source: (Collinson (No Date))].
𝑊ℎ𝑒𝑟𝑒:
𝑃 = 𝑃𝑜𝑤𝑒𝑟 (𝑊𝑎𝑡𝑡𝑠)
𝑉 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉𝑜𝑙𝑡𝑠)
𝐼 = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴𝑚𝑝𝑠)
The general term for AC resistance is impedance and given the symbol Z (Collinson (No Date)). The
AC resistance was calculated using the following equation:
𝑍 = 𝑉/𝐼
Equation 7.ii. [Source: (Collinson (No Date))].
𝑊ℎ𝑒𝑟𝑒:
𝑍 = 𝐴𝐶 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑂ℎ𝑚𝑠)
!
!
R!Load!
V(s)!!
From!Dynamo!
I!>!
Figure 12 - Schematic of Electrical System
16. Page 15 of 31
The results attained from the testing can be seen in table 3 below.
Voltage (Volts) Current (Amps) Power (Watts)
[Calculated]
AC Resistance (Ω)
[Calculated]
24 0.23 5.5 104.35
22 0.26 5.7 84.6
21 0.29 5.9 72.4
18 0.3 5.4 60
15 0.34 5.1 44.12
Table 3- Results & Calculations from Electrical Optimisation
All results collected were tested with the initial calculated angle of attack at 28.5° and fixed position
relative to wind source. Appendix I contains images taken from the electrical calibration testing
8. Wind Turbine Testing
Once the electrical system had been optimised, the angle of attack for the blades was optimised.
This was achieved by keeping the load constant and varying the angle of attack of the blades. During
testing, the distance between the fan and wind source was kept constant. The results collated from
the wind turbine testing can be seen in table 4 below. During the testing of the 40° angle of attack,
the stress in the system caused one of the M3 bolts in the hub to shear and fail. This was fixed and
re-tested, the image of the failure can be seen in appendix J.
Angle Of
Attack
(Degrees)
Speed
unloaded
Speed with
load
Current
Voltage
Unloaded
Voltage
Loaded
Power
Watts
(Loaded)
[Calculated]
20 162 112 0.200 17.5 14.0 2.8
28.5 300 168 0.290 37.0 21.0 6.09
35 360 215 0.370 39.0 27.5 10.175
40 415 300 0.412 44.0 31.7 13.06
Table 4 - Results from Wind Turbine testing
9. Discussion
When designing the wind turbine blades, it was important to consider the environmental impacts of
the project both locally and globally, and seek sustainable solutions in accordance with the UK
Government’s Sustainable Development Strategy (Guidance on Sustainability, 2015). Design
decisions were supported by a life cycle assessment which assessed the full range of environmental
effects involved in the design and manufacture of the turbine blades with particular attention to the
product life cycle of the materials used. Design was therefore focused on using renewable materials
such as the recyclable aluminium foil. According to Earth911, "it takes 95 percent less energy to
make aluminium from recycled aluminium, versus using virgin material from bauxite ore (Keen For
Green, 2015).
The turbine blades were also designed carefully to be efficient and produce the most power with the
given power input.
17. Page 16 of 31
10. Conclusion
The report has shown the process undertaken to design, manufacture and test the three wind
turbine blades. It has been shown that the design is capable of producing 13.06 Watts enough
power not only to light the lamp but to blow it.
It was also found during the testing that both the electrical load and system setup could be
calibrated in order to achieve optimal performance. It was found that an angle of attack of 40°
creating maximum power when connected to a purely resistive load of 72.4Ω.
During the testing it was found that the rig in which the turbine blades were connected to had
significant design flaws in that, it was unable to handle the stress forces created by the rotational
speeds achieved by this design.
In conclusion, it was demonstrated in the report and testing that the design was capable of
exceeding the design requirements set out in the product design specification and that the aims set
out at the beginning have been achieved.
18. Page 17 of 31
References
Collinson, (No Date) Ohm’s law for AC Circuit. [ONLINE] Available at:
http://www.zen22142.zen.co.uk/Theory/ohmac.htm (Accessed: 03 May 2015)
Guidance on Sustainability, Engineering Council, 2015. [ONLINE] Available
at:http://www.engc.org.uk/engcdocuments/internet/Website/Guidance%20on%20Sustainability.pdf. [Accessed 10.05.
2015].
Holden, H (2011) The Dynamo & Alternator Emulator . Available from:
http://www.worldphaco.net/uploads/EMULATOR.pdf [Accessed: 04 May 2015]
Keen For Green, Can You Recycle Tin Foil? 2015, [ONLINE] Available at:
http://www.keenforgreen.com/recycle/is_tin_aluminum_foil_recyclable. [Accessed 10 May 2015].
Larson, E.W. & Gray, C.F. (2011). Project Management - The Managerial Process. 5th ed. New York: McGraw- Hill.
Newton, R. (2009). The practice and theory of project management – creating value through change. 1st ed. New York:
Palgrave McMillan.
Piggott, H., 1995, Windpower Workshop – Building Your Own Wind Turbine, Centre for Alternative Energy Publications,
Edition 2004
Ragheb, M., 2014, Optimal Rotor Tip Speed Ratio, 3/11/2014,
Availaible from: www.mragheb.com (accessed on 10/04/15)
Technical Service Information DH-3N71 (2006). Available from:
http://bike.shimano.com/media/techdocs/content/cycle/SI/HubDynamo/DH-3N71/2ZR0B-DH-3N71-
EN_v1_m56577569830600105.pdf [Accessed: 03 May 2015]
19. APPENDIX A – Project Planning
Work Breakdown Structure
26. Page 6 of 31
Station Chord Lengths and Rib Angles For 4412 Aerofoil Profile Final Blade Design at
400rpm.
Station
Number
Chord
Length
[mm]
Length of
Blade
[mm]
Angle of
Twist
[mm]
1 147 40 0.00
2 150 75 12
3 147 110 20
4 140 145 27
5 130 180 33.5
6 116 215 39
7 103 250 43.5
8 91 285 47.5
9 80 320 51
10 70 355 54
11 61 390 56
12 47 425 58.5
13 47 460 60
27. C-1
Appendix F: Forces, Bending Moments and Deflection
Detailed Calculation of the Velocity Pressure, Forces and Resultant Bending moments and Deflections for the Wind turbine Blades
28. C-1
Appendix G: Cost breakdown
Detailed breakdown of materials and labour costs required for manufacturing a set of three wind turbine blades
No Materials
Quantity
per blade
Materials
cost
(£)
per blade
Total
Quantity
for 3 blades
Total
Materials
cost
(£)
for 3 blades
Assembly
time
(minutes)
per blade
Total
Assembly time
(minutes)
for 3 blades
Labour
cost
(£)
per hour
Labour
cost
(£)
per blade
Total
Labour cost
(£)
for 3 blades
1 M3 threaded rod 0.3 mtrs 0.70 1 mtr 2.10 5 min 15 min 10.00£ 0.83 2.50
2 M6 threaded rod 0.3 mtrs 0.90 1 mtr 2.70 5 min 15 min 10.00£ 0.83 2.50
3 M3 hexagonal nuts 12 0.64 36 1.92 5 min 15 min 10.00£ 0.83 2.50
4 M6 hexagonal nuts 13 0.79 39 2.37 5 min 15 min 10.00£ 0.83 2.50
5 Alluminium bar Ø8 1 3.60 3 10.80 40 min 120 min 10.00£ 6.67 20.00
6 MDF base Ø15 1 0.42 3 1.26 40 min 120 min 10.00£ 6.67 20.00
7 Alluminium foil tape 3 mtrs 1.35 9 mtrs 4.05 20 min 60 min 10.00£ 3.33 10.00
8 Blade ribs 12 2.90 36 8.70 20 min 60 min 10.00£ 3.33 10.00
9 Ballancing N/A 0 N/A 0 10 min 30 min 10.00£ 0.17 0.50
11.30£ 33.90£ 2.5 hours 7.5 hours 23.50£ 70.50£
Notes:
Total
1. Electrical parts not included
2. Workshop machinery and depreciation of assets not included
3. Overheads, marketing, transportation etc. cost not included
