1. 1
Mechanical Engineering
Individual Investigative Project
Finite element Analysis of Wind Turbine Smart Blades with respect to finding the best
Elastic Coupling Configuration
Nicholas Cadden
March 2016
Supervisor: Alireza Maheri
Dissertation submitted to the University of Northumbria in partial fulfilment of the
requirements for the degree of Bachelors of Engineering
2. 2
Abstract
The purpose of this paper is to determine the best elastic coupling configuration for the
NREL 5MW bend twist adaptive wind turbine smart blade. ANSYS, (an FEA design
tool) provides the platform for my simulations by plotting stress and deformation
patterns impacting upon the blade. In addition, ply angles and lay up configuration can
be reformed in order to find the most viable distribution. The bend-twist adaptive blade
is assumed to be made out of anisotropic composite materials. The designed blade has
the same aerofoil as the original blade used on the wind turbine, but with a different
pre-twist distribution.
Nomenclature
K effective bend-twist stiffness in blade
M flap bending moment
P rotor mechanical power
pitch pitch angle
R (i) rotor radius, (ii) Rayleigh PDF
Rhub hub radius
r radial distance from the rotor centre
tmax aerofoil maximum thickness
V wind speed
β induced twist due to elastic coupling
βo blade pre twist
βe elastic torsional deformation in the blade
𝜃 Ply angle
𝛼 Angle of attack
Ω Rotor speed
𝜑 Inflow intake
Ω Rotor speed
Abbreviations and Acronyms
BT Bend-Twist
BTAB Bend-Twist Adaptive Blade
CAS Coupled Aero-Structure
FE Finite Element
HAWT Horizontal Axis Wind Turbine
BT Bend-Twist
ST Stretch-Twist
3. 3
Subscripts
G geometry-dependant part
M material dependant part
m Matrix
ref reference
f Fibre
hub Hub
I Cut-in
O Cut-out
T Tip
* Normalised, dimensionless
Keywords: Smart blade; Wind turbine; Adaptive blade design; Bend twist adaptive blade;
elastic coupling.
5. 5
8.1 results – topology 1………………………………………………………..….34
8.2 Results – topology 2…………………………………………………..….……40
8.3 Discussion………………………………………………………………..…....45
9.0 Conclusions…………………………………………………………………...….……47
10.0 Recommendation……………………………………………………………….……48
References………………………………………………………………………..…….….49
Bibliography………………………………………………………………………….…...52
Appendix A: Experimental Plan………………………………………………….……….53
Appendix B: Energy production associated with a wind turbine blade……………….….56
Appendix C: Induced Twist; single-step (SS) and coupled aero structure (CAS)
simulation…………………………………………………………………………...….….56
Appendix D: Tip induced twist …………………………………………………..….....…56
Appendix E: Tip induced twist. FEA based and non-FEA-based CAS simulations…...…57
6. 6
List of figures
Figure 1 Ashby diagram showing various material properties
Figure 2 Bidirectional and unidirectional material properties
Figure 3 a Quasi-isotropic material lay-up
Figure 4 A warp clock
Figure 5 the early experience of static blade testing using sandbags
Figure 6 Static testing of a long blade using ballast weights
Figure 7 Static testing of a marine turbine blade using hydraulic
Figure 8 Static Testing of 1st STAR Blade
Figure 9 A STAR prototype blades in NREL test stand with loading saddles
Figure 10 elastic coupling topologies
Figure 11 Elastic coupling types
Figure 12 – Force vectors on an airfoil
7. 7
1.0 Introduction
A correctly configured wind turbine smart blade is essential to the wind turbines ability to
harness energy efficiently, vast amount of resources are being spent in to research and
development of wind power. Various compositions of wind turbine blades exist all with
differing degrees of success; this paper explores adaptive (also known as smart) blades. More
specifically, research into elastic coupling techniques of different topologies and blade
configurations. For the purpose of this paper, three main sectors are apparent throughout; the
material selection process, the FE based design tool known as ANSYS, and exploration of
BTAB elastic coupling configurations. These sub sections are highlighted below.
Fibrous composite materials have a unique structural advantage as it is possible to
incorporate elastic couplings integral to the blades design. [1] "This approach is known as
‘adaptive’ or ‘smart blades’ employs the blade itself as the controller to sense the wind
turbine run condition and flow variations and adjust its aerodynamic characteristics to affect
the wind turbine performance." (Maheri, Noroozi, and Vinney, 2007). [2] (Garfinkle and
Pastore, 2011) state that "Intrinsically-Smart (Passive) - The symmetry and balance of the
composite filament plies controls the elastic deformation response to loading of the
composite structure. Extrinsically-Smart (Active) - The sequence of actuation of piezoelectric
or magnetostrictive actuators embedded between the composite plies controls the elastic
deformation response to loading of the composite structure."
Presently, BTAB (bend-twist adaptive blades) are predominantly made of GRP (glass
reinforced polymer), the use of CFRP (carbon fibre reinforced polymer) and other polymers
can be utilized to reduce weight and cost. Reliability along with a good strength to weight
ratio are the primary factors for the GRP materials selection.
Highlighted by the work of [Lobitz DW, Veers PS, Laino DJ 2001], research towards
exploring the potential benefits of using bend-twist adaptive blades (BTAB) have shown that,
theoretically, these blades can be used to enhance the energy capture capabilities and
decrease the fatigue loading [3].
Current computer programming techniques such as FEA allows us to accurate reconstruct
turbine blades with numerous flexible variables in order to run effective evaluations for
8. 8
improvement. Due to the nature of computer modelling advances are constant as key
variables are adaptable within the program meaning a large selection of variables can be
evaluated in a short space of time thus easily finding the most efficient and viable
combination of material, structure and cost.
Pre twist distributions, ply angles, lay up configurations and elastic coupling techniques are
all contributing factors to the type of smart blade that is being produced. In this instance, a
mirror lay-up will generate bend-twist coupling in which the bending moment also produces
the torsional moment. With regards to specific Bend twist adaptive blades, [4] “the induced
twist is the structural response of the blade to its aerodynamic characteristics.” [Maheri A,
Noroozi S, Toomer C, Vinney J.2006] because of this, an FEA based solving tool is needed
in order to simulate and accurately predict mathematical, aerodynamic and design patterns.
Additionally, to the aerodynamic characteristics of the blade many structural and material
parameters are also involved. Consequently, full, accurate design and analysis of Bend twist
adaptive blades cannot be mastered without the necessary level of design, material selection,
structural properties and blade configuration knowledge.
In general, rotor blades have different structural parts, each of them for a particular purpose.
Namely, skin shell and spars are the load-carrying parts, the internal filler foam maintains the
shape of the aerofoil and the leading-edge cap protects the blade skin from erosion. Since the
effect of internal filling parts in load carrying is negligible, a rotor blade can be analysed as a
single-or multi-cell closed thin/thick-walled beam. [5] The work being carried regarding
elastic coupling configurations carries considerable significance to enable maximum
efficiency of future wind turbine blades. The use of FEA tools offers an essential and cost
effective alternative to physical work piece testing, the significant advances in design
modelling capabilities enables a large amount of credible results to be extracted which is
contributing to research and essentially, blade design and manufacture.
9. 9
2.0 Literature Survey
2.1 Initial observations
With the help of current software, having the ability to re-create a wind turbine possesses
several advantages, namely, and most importantly, being able to extract results and data of
various combinations of materials or compositions without the need for hours and man power
to physically design, build and erect the wind turbine itself. Unfortunately, this method of
design has to take into account many discrepancies and assumptions. For example the forces
the blade would be subject to can only be simulated and not fully replicated, additionally, as
previously mentioned, the mesh utilised in FEA is only accurate to a certain degree, as time
and manipulation would be threatened if the mesh was refined too much. In addition, with
the increase in design simulation capabilities, workers need to be adequately skilled in the use
of software in order to maximize the software’s capabilities, in turn directly impacting the
resulting efficiency.
Questions are raised as to the quality and reliability of such design software tools, specifically,
the degree of which real life conditions can be accurately measured and accounted for. A
consequence of this is the in-ability to precisely re-enact wind flow and patterns accounting
for the constant change in wind direction and uneven velocities. This has a direct impact on
the reliability of the result and applicability to a real life wind turbine blade.
2.2 Material selection
The material selection process is vital in obtaining the best elastic coupling configuration.
The composites materials included for analysis are:
Epoxy_Carbon_UD_230GPa_Prepreg
Epoxy_Carbon_Woven_230GPa_Prepreg
Epoxy_EGlass_UD
Resin_Epoxy
The composite materials are to be distributed between the various components of the aerofoil
elastic coupling configuration in order to compare the outcome when running different
combinations.
10. 10
There are several motives as to why these composite material polymers are being used as
primary material for smart blades. GRP possess advantageous properties which can be
exploited when constructing the blade aerofoil and intricate elastic coupling configuration
within. As mentioned, one specific benefit of utilising composite materials is that elastic
coupling configurations can be induced within the structure.
Utilising CES Edu pack it is possible to compare material groups based on a specific
materials mechanical properties, particularly, Young’s Modulus (GPa) vs Density (KG/M^3).
Figure 1[Eker A. A. and Eker B. (2013)] illustrates the properties of various material groups
in relations to the required properties for a wind turbine smart blade.
It can be seen that composites as a whole possess a ratio of elasticity to volumetric mass
desirable making it a prime material for this application.
Figure 1 Ashby diagram showing various material properties [5]
Fiber-reinforced composite materials have been broadly used in various aspects of
engineering disciplines due to their proven advantages such as;
11. 11
high stiffness to strength weight ratio
corrosion resistance
high impact strength
design flexibility
Particularly, when thin walled composite beam like structures are tailored by using the proper
elastic coupling layups, bend –twist and/or stretch/twist would be introduced. One particular
application of this type of material is manufacturing smart and adaptive aerodynamic lifting
surfaces employed in wind turbine adaptive blades.
As previously mentioned, ply angles (fibre orientation) are a large contributing factor to a
blades success. The resultant outcome is determined by the orientation of the plies in
correlation to the applied load. Suitable selection of ply orientation in advanced composite
materials is necessary to provide a structurally efficient design. Ply orientation and ply
sequence have to be precise. It is critical during a repair to replace each damaged ply with a
ply of the same material and ply orientation. The fibers in a unidirectional matrix run in one
direction and the resulting strength and stiffness is only in the direction of the fiber. Pre-
impregnated (Prepreg) tape is an example of a unidirectional ply orientation. The fibers in a
bidirectional material run in two directions, typically 90° apart. A plain weave fabric is an
example of a bidirectional ply orientation. These ply orientations have strength in both
directions but not necessarily the same strength (Fig. 2)
Figure 2 Bidirectional and unidirectional material properties [6]
The plies of a quasi-isotropic layup are stacked in a 0°, –45°, 45° and 90° sequence or in a 0°,
–60° and 60° sequence. (Fig. 3) These types of ply orientation simulate the properties of an
12. 12
isotropic material. Many wind turbine blades composite structures are made of quasi-
isotropic materials.
Figure 3. Quasi-isotropic material lay-up.[6]
Warp indicates the longitudinal fibers of a fabric. The warp is the high strength direction due
to the straightness of the fibers. A warp clock is used to describe direction of fibers on a
diagram, spec sheet, or manufacturer’s sheets. If the warp clock is not available on the fabric,
the orientation is defaulted to zero as the fabric comes off the roll. Therefore, 90° to zero is
the width of the fabric across.[6] [Figure 4]
Figure 4 A warp clock
Studies done by Brøndsted, P. (2013), found that restrictions were encountered in early
blades because of the need to handle both epoxy and polyester. This resulted in considerable
variation in laminate quality as well as serious working environment problems.
13. 13
Conversely, Modern manufacturing methods are dry lay-up followed by vacuum infusion.
The increasing demand for both fibres and resin generates and develops markets for new
suppliers and calls for additional quality assurance for the raw materials deliverables.
Quality assurance is vital to ensure consistency in the manufacturing processes. Most
importantly, blades and blade materials suppliers must ensure the dependable quality of their
fibres, sizing’s and resins to fulfil basic legal requirements, and the final composite properties
are very dependent on consistency between fibre surface treatments, resin quality and
manufacturing parameters. [7] Subsequently to achieve a consistent batch strict protocols and
guidelines are to be adhered.
2.3 Finite Element Analysis
ANSYS offers an accurate and dependable creation based on the input variables. Specifically
Ansys can be defined as, "a self-contained analysis tool incorporating pre-processing
(geometry creation, meshing), solver and post processing modules in a unified graphical user
interface." [8](Kim, Sankar, and Nam-Ho, 2008, pp. 363 – 364)
Unorthodox anomalies make anisotropic materials difficult to be FE modelled analytically.
This is because anisotropic composite materials have inherent unusual behaviours like large
torsional warping (see figure 4), coupled in-plane and out-of-plane warping, transverse shear
strain, 3-dimensional strain effects and non-uniform shear stiffness.
Historically, a vast amount of research on analytical modelling of thin and thick walled
beams made of anisotropic composites has been carried out, but they have been limited to
either simple geometries, or they account for only some or none of the effects; a prime
example being the fact that the required accuracy for predicting the induced twist is very
high, (e.g. a twist angle of about one degree can affect the energy capture capability of the
unit or the blade loading significantly [9]), together with the current deficiencies in the
available analytical models, have placed the finite element (FE) techniques to the fore with
respect to analysis of the induced twist in adaptive blades.
In BT smart blades the source load for the induced twist is the aerodynamic force which
depends upon various aspects, namely the rotor angular velocity, wind velocity, the blade
topology and its aerodynamic characteristics. In these blades the source load affects the
14. 14
induced twist and the induced twist affects the source load. In other words there is an
interaction between the induced twist and the source load. This interaction makes simulation
of wind turbines with BT blades an iterative coupled aero-structure (CAS) process. In a CAS
simulation, the effect of the induced twist on the initial loading situation is taken into
account. Correcting the load, induced twist will be re-calculated. This sequence repeats until
a converged solution is achieved. A schematic description of a CAS simulation is shown in
Figure (4). [10]
As formerly stated, the work being done via FEA offers a 3D simulation for the blade,
Physical testing alongside design software is required to gain an alternate approach and offer
a life like component to results. Research of by Wenxian Yang (2013) [11] highlights
alternate Static Testing Methods and Systems.
The purpose of the static testing is to predict the blade capability of withstanding ultimate
loads as those caused by storm, hurricane, typhoon or others happening in extreme weather.
The objective of this type of testing is to determine and/or verify the ultimate strength of the
blade through analysis of the testing results, which could be the distribution of strains along
blade length under different static loading conditions or other related information.
In static testing, distributed loads are applied to the blade statically in one direction to
establish the required ultimate strength. Such a test can be performed in a number of ways. In
the very early days of the wind industry, static testing of wind turbine blade was conducted
by placing sandbags along the blade length to mimic the bending moment distribution, as
shown in Fig. 4.
Fig. 5 The early experience of static blade testing using sandbags [11]
15. 15
Wenxian Yang (2013) [11] goes on the compare different testing techniques and their
progressions. Ballast weights were hung at specific locations of the blade to create the
expected static loads. In the case of testing long blade, the blade under investigation will
usually be attached to the test stand at a specific angle in order to prevent the tip of the blade
from touching the ground, as shown in Fig. 6.
Fig. 6 Static testing of a long blade using ballast weights [11]
In the past, hydraulic actuators were also experienced for creating the expected bending
moment loads along the blade length. But the large deflections resulting from long wind
turbine blades under static testing make them an expensive option. For this reason, today
hydraulic actuators are rarely used in the static testing of large wind turbine blades. However,
they are often adopted in the static testing of marine turbine blades attributed to their short
length, as seen in Fig. 7. [11]
Fig. 7 Static testing of a marine turbine blade using hydraulic actuators [11]
16. 16
Similarly, (D. Ashwill§ et al., 2010) Development of the Swept Twist Adaptive Rotor (STAR)
Blades undertook some similar static testing with a different approach.
The first blade was tested statically in the flatwise direction at K&C facilities at three load
levels – 50% and 100% of maximum operating load and proof load. Figures 8 and 9 show the
static test arrangement including the unique barrel-type loading configuration (barrels were
filled with water to different levels to produce desired load inputs). Both flatwise and twist
deflections were carefully measured resulting in the verification of the predicted twist
response expected by the swept nature of the blade.
Figure 8. Static Testing of 1st STAR Blade [12]
Figure 9 a STAR prototype blade in NREL test stand with loading saddles. [12]
Fatigue Test. The first STAR blade produced in Knight & Carver’s new Howard, South
Dakota factory was chosen for the NREL fatigue test. The fatigue blade was built in October
17. 17
of 2007 and shipped to NREL in January of 2008. It included modifications to the shear web
and spar cap that were made based on the static test. The loading was applied primarily in the
flatwise direction to allow for the simultaneous testing of flatwise bending and torsional
twisting to determine the amount of the bend-twist coupling achieved. The first phase of
testing was designed to test the outboard portion of the blade where the bend-twist response
is greatest. Figure 14 shows the blade in the test stand with the primary loading and load
trimming saddles in position. Loads were applied through a pair of saddles centred on the 11
m station, and the load distribution was adjusted via two additional saddles at the 18 m and
23 m stations, which were weighted to achieve the desired load profile. This choice placed
the loading saddles away from the 12– 13 m region where inner skin crazing had been noted
in the earlier static test, and the region near 15 m where peak torsional shears were expected
to occur.
The initial loading phase tested the blade outboard of the 13 m station to at least a full 20 year
equivalent life.
The second phase of testing increased the blade loading in the inner region so that portion of
the blade could be more thoroughly tested. Cycling resumed until a full 20 year lifetime
equivalent damage load was obtained for all blade stations outboard of 5 m. The test was
stopped with 2,660K cycles and much of the blade having been exercised to about three times
the target 20 year equivalent life. Strain and stiffness data were essentially unchanged since
the test began. [12]
2.4 BTAB – elastic coupling configuration
Figure below (a)-(d), shows four different cross sections of elastic coupling locations, in this
case, they are located on the entire suction and pressure side, D-Spar, Cap of one web and cap
of two webs respectively. Figures (e)-(f) highlights the distribution of elastic coupling along
the span of the adaptive blade.
18. 18
Figure 10 Elastic coupling topologies
It’s worth noting, the figures indicates that the cross sectioned areas are unbalanced layups
and the non-cross sectioned areas are balanced layups. This refers to the material
composition and the way in which the layers are compiled to produce specific materials and
properties.
The ‘Performance Prediction of Wind Turbines Utilising Passive Smart Blades’ paper
(Maheri et al 2010) [13] explores various elastic couplings, which are the result of the
specific lay-up and fibre orientations, can be induced in a structure constructed of fibre
reinforced composites.
Different lay-ups can be used to achieve different types of couplings. A helical lay-up makes
the blade a stretch twist coupled structure in which the axial load produces the torsional
moment. Different levels of elastic coupling can be achieved in the blade by changing the ply
angle_ in the layers that comprise such material, the shell thickness as well as the fibre and
matrix mechanical properties. These structural couplings can have favourable influences on
the aero elastic behaviour of the blades. Figure 11 below illustrates two types elastic coupling;
these blades can be classified as either bend-twist (BT) or stretch-twist (ST) smart blades.
19. 19
Figure 11. Elastic coupling types [13]
Available in appendix C, D and E is various Maheri et al approaches involving Wind turbine
smart blades with reference to induced twist and tip induced twist simulations.
Similarly, Appendix C (A computer program for predicting the performance of horizontal
axis wind turbines with adaptive blades) highlights induced twist as a function of the blades
span with respect to different simulation types. Appendix D shows tip induced twist as a
function of wind speed seen in (Combined analytical/FEA-based coupled-aero-structure
simulation of wind turbines with bend-twist adaptive blades), and appendix E offers insight
into present FEA based simulations contrasting with present methods found in (Decoupled
aerodynamic and structural design of wind turbine adaptive blades).
2.5 Ethics
Wind power is potentially a source of clean, limitless energy. It’s abundantly clear that the
harnessing of wind energy has countless advantages and beneficiari19es. Problems occur to
society regarding placing the turbines in suitable locations for environmental and social
motives with questions raised over wind turbines efficiency, consistency and safety fears to
supply for the worlds increasing demands when compared to current alternatives. If captured
correctly, wind turbines could help eliminate the need for coal as a source of energy across
large parts of the world. Thus removing the need for energy supplied from coal and other
20. 20
harmful means, ultimately contributing to the elimination of greenhouse gases and pollution.
Current trends of wind turbine research and development into the advancements in wind
turbine technology, gives a great indication as to the potential figure in which wind turbines
can be contributing to the world’s energy consumption in the near future.
2.5.1 Disposal
With increased production rate of wind turbine blades comes greater recycling and disposal
issues. Currently, the most common methods of disposing of wind turbine blades are landfill,
incineration, recycling. Specifically, glass fiber reinforced plastics (GFRP) are generally
disposed of via landfill; a consequence of this is high gas content (methane) that is released
into the atmosphere once the blade begins decomposition. Alternatively, GFRP’s can be
incinerated, an advantage of this process is the material being incinerated can contribute to
additional energy production extracted from the heat released, precisely, this process of
incineration of a blade with 70% E-glass/30% epoxy resin composition, can recover is
approximately 8% of what was consumed during manufacturing. Finally, wind turbine blades
can be recycled utilising a process known as pyrolysis, this method heats the material to
separate it in to its original elements without consuming any oxygen. Similar to incineration,
the resultant gases can be heated to produce electricity. Unfortunately, the demand for this
process is not high enough to warrant a plant solely for GFRP recycling making the current
process financially impracticable. [14]
2.5.2 Sustainability
Wind turbine blades have an very high sustainability factor provided the correct care,
maintenance and provision are achieved, in order to preserve and maximize efficiency and
life span of a wind turbine the blades need to be sustained. Additionally, by definition, any
structure capable of harnessing wind power to produce energy will provide a superior energy
output to input ratio. Research done by C.Owens et al (2013) [15] The energy required to
produce a turbine blade has been calculated as 50900 kWh. Thus, in the 20 year usage phase,
the turbine blade will recover energy used in manufacturing in about 3 weeks, with a net
energy yield of 17.5 GWh in its lifetime.
21. 21
3.0 Theoretical Analysis
Aerodynamic Lift and Drag Coefficient
The dimensionless values of lift coefficient and drag coefficient are universally used in
aerodynamic analysis and are shown by Equation 1 and Equation 2 respectively.
These are used to link the relationship between the resultant forces due to the nature of the
fluid, in this case air, flowing around the body, specifically, a wind turbine blade.
𝐶 𝐿 =
𝐹 𝐿
1
2
𝑃 𝑣2
𝐶 𝐷 =
𝐹 𝐷
1
2
𝑝 𝑣 2
Whereby;
𝐶 𝐿= Lift Coefficient
𝑃 = Air Density, kg/m³
𝐶 𝐷= Drag Coefficient
𝐹𝐿= Lift Force, N
𝑣 = Drag Force, N
𝐹 𝐷= Air Velocity, m/s.
Rearranging the equations above gives Equation 3. and Equation 4. shown below;
𝐹𝐿 =
1
2
𝑝 𝑣2
𝐶𝐿 𝐹𝐷 =
1
2
𝑝 𝑣2
𝐶𝐷
Reference to the above concludes that, applied to the flow of air over a blade, the lift force
and drag force experienced will increase proportionally with an increase in air velocity.
Given that for a specific scenario the values for air velocity in Equations 3 and 4 are equal, it
is also true that the greater the lift force on a body, the greater the drag force. [16]
22. 22
Figure 12 – force vectors on an airfoil [17]
As seen via the figure 12 the lift acting upon a turbine blade is perpendicular to the direction
of the air flow, whereas drag always acts in the direction of the incoming flow of air. The
resultant of the forces applied to the airfoil is the generation of lift, which always creates
drag.
3.1 Angle of attack
Maheri et al 2010 [18] research involving performance prediction of wind turbine smart
blades established that The magnitude and direction of the aerodynamic forces applied on the
blade and consequently the blade and wind turbine performance strongly depend on the blade
angle of attack. Angle of attack is dependent on the inflow angle and twist angle of the blade,
additionally, wind velocity and rotor angular velocity define the inflow angle. The resultant
Blade twist angle is a arrangement of three angles: pre-twist distribution, pitch angle and
elastic torsional deformation of the blade. Equation (3.1) expresses the angle of attack in
terms of other angles.
𝛼 = 𝜑 + 𝛽𝑒 − 𝛽0 – 𝜌 (Equation 3.1)
In the above equation;
𝛼 , 𝜑 and 𝛽𝑒 are used for the angle of attack, the inflow angle and the elastic torsional
deformation respectively.
𝛽0 and 𝜌 are the blade pre-twist and pitch angle.
23. 23
3.2 induced twist
Further research of (Maheri et al 2007) [19] into Decoupled aerodynamic and structural
design of wind turbine adaptive blades found that in order to establish the induced twist as an
independent aerodynamic design parameter, the results of the semi-analytical model of a
bend–twist coupled blade developed in Ref. [20] can be seen. A bend–twist coupled blade
was considered as a thin/thick-walled beam with circumferentially asymmetric stiffness
(caused by mirror lay-up). Application of the force–displacement relations of Kim and White
[17] two simplifying assumptions have been reduced to a single equation relating the blade
induced twist to the flap bending. The simplifying assumptions are shown as;
1. comparing with the flap-wise slope and twist of the blade, the edge-wise slope of the
blade is negligible
2. The influence of the internal torque due to the off-axis aerodynamic loading of the
blade, in comparison with that of the torque produced due to elastic coupling, in
generating the induced twist is negligible.
The equation correlating the induced twist in a BTAB to the flap bending is:
𝛽( 𝑟 ∗) =
𝑀ℎ𝑢𝑏
𝐾𝑚𝑎𝑥
∫
𝑀∗( 𝑟∗)
𝐾( 𝑟∗)
𝑟∗
0
𝑑𝑟 ∗ (Equation 3.2)
In the equation above;
M* = M/Mhub designates the normalised flap bending; M hub is the flap bending at
blade hub.
Kmax stipulates the maximum effective torsional stiffness of the blade, dependent
upon the material and structural properties of the blade
K* = K/Kmax represents the normalised effective stiffness, a function of span-wise
variations of the material and structural properties of the blade rather than material
and structural properties of the blade.
r* =(r-Rhub)/(R-Rhub) is the normalised radial location; r being the radial axis, with
its origin located at the centre of the rotor; additionally R and Rhub are rotor and hub
radius, respectively.
24. 24
They also showed that the normalised flap bending moment, M*, is a very weak function of
wind turbine run-condition. Then, referring to this fact that the effective stiffness K =
K*_Kmax, does not depend on the wind turbine run-condition either, they concluded that the
term (1/Kmax) ∫ 𝑀 ∗
𝑟∗
𝐾∗
𝑟∗
0
( 𝑟 ∗) 𝑑𝑟 ∗ in Eq. (1) can be considered as invariant with the wind
turbine run-condition. The induced twist produced in a BTAB varies only due to the variation
of the flap bending moment at the hub, Mhub (as a result of the variations of wind turbine
run-condition). Ultimately, once the induced twist, 𝛽( 𝑟 ∗) at a reference run-condition is
given, it can be used for prediction of 𝛽( 𝑟 ∗)at other wind turbine run-conditions as follows:
𝛽( 𝑟 ∗, 𝑉,Ω, 𝑃𝑖𝑡𝑐ℎ) = 𝑀ℎ𝑢𝑏 (𝑉, Ω, 𝑃𝑖𝑡𝑐ℎ)
β(r∗)ref
𝑀ℎ𝑢𝑏,𝑟𝑒𝑓
(Equation 3.3)
In which;
β(r ∗)ref = 𝛽( 𝑟 ∗, 𝑉 𝑟𝑒𝑓, Ω ref, 𝑃𝑖𝑡𝑐ℎ 𝑟𝑒𝑓) is the reference induced twist
Mhub,ref = Mhub(Vref, Ω ref, pitchref) is the reference flap bending at the hub of the
blade. Since Mhub depends on the wind turbine run-condition and the blade
aerodynamic characteristics, calculated only from a non-FEA-based CAS simulation.
3.3 normalised induced twist
The induced twist 𝛽(𝑟)is expressed by a combination of two independent parameters:
1. Normalised span-wise distribution of the induced twist, 𝛽 ∗ (𝑟). Normalised induced twist
is a dimensionless parameter limited between 0 at the hub and 1 at the tip of the blade and
refers to the span-wise trend of induced twist.
2. Maximum value of the induced twist at the tip of the blade, 𝛽𝒯. Tip induced twist is a
parameter indicating the level of elastic coupling in the structure of the blade and the
intensity of the blade aerodynamic loading. Using these two parameters, the induced twist
can be written as;
𝛽( 𝑟 ∗) = 𝛽 ∗ (𝑟 ∗)𝛽𝒯 (Equation 3.4)
25. 25
3.4 Tip induced twist
Extending the work seen in 3.1 it is seen that since K*(r) depends on the span-wise variation
of the blade cross-section geometry, shell thickness and material properties, developing an
analytical model for predicting K* should not be difficult. On the other hand, wind turbine
aerodynamic simulation gives the normalised flap bending distribution, M*. Therefore,
having an analytical model for K* embedded in a traditional wind turbine simulator, the
normalised induced twist, 𝛽 ∗ can be calculated. It leaves the tip induced twist, 𝛽𝒯 as the
design parameter.
Dividing Eq. (3.2) by the normalised induced twist, 𝛽 ∗ gives the tip induced 𝛽𝒯 as follows:
𝛽𝒯 =
𝑀ℎ𝑢𝑏
𝑀𝑟𝑒𝑓
𝛽𝒯, 𝑟𝑒𝑓. (Equation 3.5)
In the above equation, Mhub, as mentioned earlier, depends on the wind turbine run
condition and the blade aerodynamic characteristics
𝛽𝒯, 𝑟𝑒𝑓 Represents the material and structural characteristics of the blade.
26. 26
4.0 Constraints and Limitations
Whilst modelling the wind turbine smart blade in solid works and ANSYS workbench 16.0,
certain complications have arisen. A primary example would be the inability to render a
solution after applying the pre-twist distribution in solid works. The blade requires an
integrated pre-twist in order to accurately reconstruct a real life blade; unfortunately this can
be somewhat problematic with regards to accurate conversion in model form. The pre-twist
of the blade will alter the blades dimensions and creates a warping effect as previously
mentioned (see 2.2). This has a direct effect on the mesh sizing and material thickness. The
resultant of this on the blade was an overlapping distribution between the leading edge and
trailing edge meaning a solution could not be rendered. To overcome this problem the chord
length had to be altered, (three times the original) essentially making the blade wider,
allowing more room inside the blade to compensate for this problem. Additionally, naturally
as the file became bigger and more variables added ANSYS’ ability to manage the number of
iterations decreased. This was due to the mesh’s size and the amount of information stored at
each node. This had a knock on effect to the solution time making it somewhat slow and
inefficient. As mentioned the mesh sizing impacted the solution time, a simple fix would be
to decrease the mesh size which would lower the number of calculations needed via the FE
tool, the main problem with this method would be the corresponding decrease in accuracy.
Finally, the fundamentals of this paper is exploring the varying effects of varying elastic
coupling configurations with respect to fluctuating ply angles for different topologies, the
resultant induced twist values are calculated for a ply angle distribution between 55 - 85
degrees. In order to fully devote my research and computational resources a selection of a
suitable and practical range of ply angles needed to be selected.
A full 90 degree perspective of all variations of ply angle would have offered a broader take
on elastic coupling configurations and resultant induced twist, unfortunately, the processing
power and added time which would be required made it impracticable.
27. 27
5.0 Project aims and Objectives
5.1 Problem statement
Naturally, any standing structure is exposed to stresses, strains and various environmental
impacts. Wind turbine blades are required to be as aerodynamically stable as possible to
combat the numerous forces impacting the blade at any given time. As ever, wind turbines
are constantly evolving and improving with regards to efficiency, through this project it is
possible to duplicate the variables in which a real wind turbine blade would experience via
complex FEA programming applications, from this we are able to compute and analyse the
elastic coupling blade variations.
5.2 Overall aim
The aim of this investigation is to configure a viable elastic coupling configuration of Bend-
twist Adaptive blade utilising two topology configurations, assuming anisotropic composite
materials, the ply-angles will be altered accordingly to produce the desired optimal elastic
coupling formation. Topology one will explore constant thickness ply angle configuration
with the resultant β* value (induced tip twist) as a basis for comparison between various lay-
up configurations. Topology two will develop varying ply angles throughout the blades span
to produce the induced twist of the blade to be presented as a function of the blade span.
5.3 Objectives
Objective 1 – To identify and apply appropriate limitations of the wind turbine smart
blade
Methodology
To elect composite materials with realistic properties, currently in use of BTAB blade
production, correctly classify and configure each section of the blade corresponding with a
specific material relevant to real life application.
28. 28
Deliverable
Systematically research and review materials composition and properties finding optimal
available materials. Customize ACP Pre setup configuration of material data; materials,
fabrics and stackups.
Objective 2 – to develop a fully functioning and applicable wind turbine smart blade
available for analysis, applying constraints and generating a model of each layup
configuration scenario.
Methodology
Create the blade using SOLIDWORKS, importing the air foil to an FE based design tool, in
this instance, ANSYS. When a fully functioning blade has been created with practical
constraints, results can be processed and rendered. Calculation of the β* value (induced twist)
can be extracted utilizing the deformation of the blade in the Y axis at any given point along
the blade or a given blade airfoil.
Deliverable
Initial constraints when designing the blade are configured, fundamentally material selections,
pre-twist distributions and mesh criterion. ANSYS requires constraints setup parameters to
enable definition of the blades entities in order to render solutions. Namely such factors as the
shell thickness, ply angles and nodal loading forces.
Objective 3 – to produce the most suitable BTAB layup configuration which produces
the most realistic total deformation and induced twist/tip values for each topology
configuration.
Methodology
Utilising various topologies creates an efficient and organised design method for comparing
data. Comparing induced twist values with respect to the blades span provides an indication
as to the viability of each lay-up configuration. These layup configurations can be compared
and scrutinised to find the most applicable values.
29. 29
Deliverable
Tabulate various elastic coupling configurations, extracting the induced twist β* value at the
tip of the blade By means of deformation in the Y axis from ANSYS. Incorporating constant
pre-twist distributions, cap percentage distributions, nodal loading force and blade shell
thickness yet varying fibre angles of the shells composition.
30. 30
6.0 Project Planning
Time (weeks)
Objective 1- 3 4 - 7 8 - 1 1 1 2 - 1 5 1 6 - 1 9 2 0 - 2 3 2 4 - 2 7 2 8 - 3 1 3 2 - 3 5 3 6 - 3 9 3 9 - 4 2
Objective 1 – To identify and
apply appropriate limitations of
the wind turbine smart blade
Objective 2 – to develop a fully
functioning and applicable wind
turbine smart blade available
for analysis, applying
constraints and generating a
model of each layup
configuration scenario.
Objective 3 – to produce the
most suitable BTAB layup
configuration which produces
the most realistic total
deformation and induced
twist/tip values for each
topology configuration.
31. 31
7.0 Methodology
7.1 Solid works
I will achieve my objectives by modelling the blade in the software programme solid works
by the importation of pre-set curves in order to produce a basic blade shell. In addition to this
the aerofoil will require a pre twist, shear web, cap and D-spar. These are necessary
components in order to accurately reconstruct a real life blade. The pre twist function
calculated at 13.308 degrees enables the blade to enhance its efficiency during its revolution
cycle and produce less drag co-efficient. The shear web, cap and spar all maximize strength
and stability for the length of the aerofoil. For the purposes of this project the blade is
applied on a NREL 5MW turbine. By means of solid works the blade can be adjusted so that
a pre-twist angle is established and a shear web is run through the blade. The shear web is a
function of the chord length of the blade and for this blade exists at 25% of the chord length
of the blade. As previously mentioned, problems occurred when modelling the blade to
specific constraints and the blades chord length was increased by a factor of three to
accommodate for the meshing inadequacies caused by the pre twist distribution added.
7.2 ANSYS
By importing the solid works file previously created into ANSYS 16.0 workbench this
provides a basis for simulation. This process utilises two different systems, Acp Pre and static
structural. ANSYS Composite PrepPost (ACP) offers all the necessary functionality for the
analysis of layered composite structures. Specifically, able to define materials, plies and
stacking sequences, Materials can be accurately oriented on the structures using very flexible
tools based on coordinate systems definitions, whilst the static structural component
incorporates the previously applied constraints and enables structural analysis of physically
properties concerning the blade.
7.2.1 Material selection
The first step is to identify which analytical system is needed form the toolbox; firstly, Acp
Pre is designated. Entering the engineering data of the project schematics gains access to all
the various attributes needed. The toolbox allows various characteristics such as Physical
properties, elasticity, strength, damage, fatigue etc. all to be altered. In addition, it is at this
section where material selection takes place, many types of materials are available but as
32. 32
aforementioned are the specific composite materials selected for this process; Carbon, EGlass
and Resin Epoxy.
7.2.2 Model - geometry, co-ordinate system, mesh, named selections
The blades geometry is now ready to be specified and boundary conditions can be set. Each
specific section has to be selected and referenced to a geometry allowing the programme to
differentiate sections. Additionally, a coordinate system is applied to give a reference point
for the blade to work from. The mesh is generated in relation to the airfoils that are being
used; the function of the mesh is to facilitate reference locations in which the blade can then
be resolved. The mesh is defined using body sizing’s and face mapped meshing, this part is
crucial to the quality and definition of the mesh’s detail. The application of a nodal loading
profile is also dependent upon a well-constructed and defined mesh.
7.2.3 Acp Pre Setup
The Acp Pre Setup is now to be configured, material data including; specific materials,
fabrics and stackups are arranged. The material selection contains all the selected composites
that were selected in from the engineering data, these materials now need to be used in order
to define each fabric. The fabric will contribute to the different layers of materials used to
form the blade. The thickness of the material is applied taking into consideration the amount
of material layers which will be needed increasing the overall thickness of each component.
The stackup section requires a fabric to be selected, and associated with a corresponding ply
angle. Layups can become complex with larger blades as more layers can be needed with
varying ply angles and thicknesses for each section of the blade. Further constraints such as
rosette geometry, modelling groups and layup plots can be found in the Acp Pre setup.
7.2.4 Static structural – fixed support, nodal force
Once the setup parameters are complete, the blades credentials can be transferred to the static
structural system which is added to the project schematic and the data dragged across. The
blade is now ready for final further constraints such as the fixed support and nodal force is to
be applied, a fixed support is applied to the face closest the hub in order to replicate the fixed
location of a physical blade.A nodal force is used to represent the wind acting upon the blade,
this can be achieved through various processes; one option is by distributing the external
aerodynamic force on the nodes, another potential way is by calculating the pitching moment
33. 33
produced by the distributed nodal forces or finally by calculating the difference between the
actual and calculated pitching moments and distributing that difference on the nodes.
7.2.5 Solution – direciton deformation, total deformations
The blade is ready to be solved and a solution rendered to the specific requirements, in this
instance deformation in the Y axis and total deformations. The resultant blade is an image
with corresponding values of deformation associated to each node of the blade. This data can
be extracted via export or viewed at each individual node using the probe tool.
7.2.6 BTAB elastic coupling configuration design method
The final step was to produce the tables and graphs needed for evaluation. As seen in section
3, theoretical analysis, the necessary equations are surplus to the deformation values taken
form ANSYS, using excel spreadsheet the deformation values for the Leading and trailing
edge can be processed through basic formulas to produce the induced twist, as seen in
equation 7.1.
𝑇𝑎𝑛𝛽 =
𝑤1−𝑤2
𝑐ℎ𝑜𝑟𝑑
eq. 7.1
Where;
w1 = Trailing edge
w2 = Leading edge
Once all the values have been collected a series of graphs comparing various topologies will
afford an insight into a viable elastic coupling configuration.
34. 34
Table1
8.0 Results and Discussion
8.1 Results - TOPOLOGY 1
chord length at the Tip (m) ply angle(ϑ) LE Def Y TE Def Y induced tip twist β (radians) induced tip twist β (degrees) max tip deformation (m)
6.27 50 -3.7012 -4.367 0.533258864 30.55348227 4.45
6.27 55 -3.576 -4.172 0.518321287 29.69762218 4.327
6.27 60 -3.4824 -3.9056 0.506984748 29.04808634 4.207
6.27 65 -3.39 -3.72 0.495651744 28.39875301 4.005
6.27 70 -3.294 -3.5149 0.483728274 27.71558856 3.894
6.27 75 -3.2028 -3.378 0.472260857 27.05855396 3.772
6.27 80 -3.1034 -3.224 0.459607589 26.33357506 3.613
6.27 85 -2.9908 -3.1728 0.445080191 25.50121648 3.5896
induced tip twist β ply angle(ϑ)
30.55348227 50
29.69762218 55
29.04808634 60
28.39875301 65
27.71558856 70
27.05855396 75
26.33357506 80
25.50121648 85
24
26
28
30
32
40 50 60 70 80 90
inducedTipTwist
Ply Angle
βTip (ᵒ) vs Ply angle (ϑ)
Table2 Graph1
35. 35
50 ply angle (θ) Table 3
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.64E-02 -6.90E-02 0.002853012 0.163465539
20.5 11.25 -0.29501 -0.60781 0.026217103 1.502129342
32.82 7.92 -1.3924 -2.2 0.174029627 9.971163162
41.02 7.56 -2.4533 -3.199 0.313789174 17.9787953
49.92 4.26 -3.7814 -4.1758 0.72595129 41.59394505
55 ply angle (θ) Table 4
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.64E-02 -0.068847 0.0028516 0.163384651
20.5 11.25 0.28452 -0.59223 0.027345182 1.566763524
32.82 7.92 -1.3268 -2.147 0.165983942 9.51017933
41.02 7.56 -2.377 -3.101 0.304631263 17.45408566
49.92 4.26 -3.653 -4.043 0.708838882 40.61347628
60 ply angle (θ) Table 5
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.63E-02 -0.068415 0.002850737 0.16333522
20.5 11.25 0.27897 -0.5793 0.026689661 1.529204923
32.82 7.92 -1.2817 -2.061 0.16043986 9.192526836
41.02 7.56 -2.302 -2.993 0.295577684 16.93535379
49.92 4.26 -3.541 -3.934 0.693490155 39.734059
36. 36
65 ply angle (θ) Table 6
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.63E-02 -0.067781 0.002850267 0.163308258
20.5 11.25 0.26729 -0.5681 0.026732297 1.531647799
32.82 7.92 -1.2004 -1.997 0.150420799 8.618476949
41.02 7.56 -2.169 -2.876 0.279399941 16.00843744
49.92 4.26 -3.492 -3.792 0.686649192 39.3421007
70 ply angle (θ) Table 7
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.63E-02 -0.067263 0.002847914 0.163173445
20.5 11.25 -0.25903 -0.5579 0.023020821 1.318995903
32.82 7.92 -1.1537 -1.8463 0.144651771 8.28793599
41.02 7.56 -2.072 -2.764 0.267505181 15.32691789
49.92 4.26 -3.337 -3.537 0.664495399 38.07278187
75 ply angle (θ) Table 8
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.63E-02 -6.70E-02 0.002846816 0.163110533
20.5 11.25 -0.25173 -0.5474 0.022372267 1.281836459
32.82 7.92 -1.1473 -1.8971 0.14386039 8.242593194
41.02 7.56 -2.0007 -2.683 0.258711993 14.8231053
49.92 4.26 -3.1659 -3.3403 0.639114924 36.61858777
37. 37
80 ply angle (θ) Table 9
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -3.59E-02 -6.43E-02 0.002817875 0.161452339
20.5 11.25 -0.25227 -0.54374 0.022420243 1.284585277
32.82 7.92 -1.1138 -1.8617 0.139715065 8.005083558
41.02 7.56 -1.954 -2.6184 0.252930288 14.491838
49.92 4.26 -3.0871 -3.24 0.627092746 35.92976772
85 ply angle (θ) Table 10
Span of Blade (m) Chord Length (m) Y Deformation at LE Y Deformation at TE Induced Twist Y (radians) induced twist Y (degrees)
0 0 0 0 0 0
12.5 12.75 -0.0357643 -0.057993 0.002805036 0.160716712
20.5 11.25 -0.25062 -0.51189 0.022273649 1.276186092
32.82 7.92 -1.0971 -1.7817 0.137646774 7.8865792
41.02 7.56 -1.9099 -2.534 0.24745456 14.17810191
49.92 4.26 -2.9908 -3.1728 0.612111014 35.07137768
45. 45
8.3 Discussion
Topology 1
Topology 1 applies a shell thickness of 2cm with a constant cap thickness of 1cm, uniform
blade ply angles for each individual layup configuration within the topology and a maximum
13.308 degree pre-twist distribution. Additionally, a nodal force of 17500Kn in the X
direction and -3500kN in the Y direction can be seen throughout.
The first part of topology one explores the induced tip twist values (β) relating to different
uniform ply angle configurations, (seen is table 1) is the values collected and calculated
regarding each individual layup; ranging from 50ᵒ ply angle (ϑ) to 85ᵒ ply angle (ϑ).
The induced tip twist β found in degrees corresponding to each layup configuration are
documented. Table 2 highlights the induced tip twist for each variation of ply angle with a
decreasing induced tip twist β being seen correlating with an increasing ply angle, generically
speaking, regarding the β value, a direct correlation between increasing ply angles and
decreasing induced tip twist can be made. Graph 1 ‘βtip vs Ply angle’ specifies the formerly
mentioned correlation between the induced tip values calculated and the increasing ply angle
showing a peak induced tip twist of 30.55 degrees corresponding to a constant 50 degree ply
angle. The maximum tip deflection is also recognised and highlights the amount of deflection
between its origin before and after loading, ranging from 3.59m to 4.45m.
Integrated into the design method of topology one is the eight variations of ply angle
configurations but this time documented across its span appose to just the induced tip twist
value. Using 5 different sections along the blade enables values to be associated at designated
airfoils, specifically 5 sections have been used and a corresponding twist value has been
given. The result of this is the induced twist at each section along the blades span. Conversely,
the induced tip twist was used with one resultant value per cycle; this method offers five
solutions per cycle and provides an induced twist assessment as a function of the blades span.
Seen in tables 3-10 are these results. A reflection of these results is characterised as
increasing ply angles suggest decreasing induced twist values throughout the blade. Graphs
(2-9) support the statement above by plotting the resultant induced twist values of each layup
against the blades span for each ply angle variant. These graphs show a distinct decrease in
46. 46
induced twist at each section ranging from increments of 1.69% increase of sections nearest
the blades hub, to a 17.0157% decrease correlating to an increasing blade ply angle
distribution.
Topology 2
Similarly, topology 2 utilises a shell thickness of 2cm with a constant cap thickness of 1cm,
uniform blade ply angles for each individual layup configuration within the topology and a
maximum 13.308 degree pre-twist distribution. Additionally, as before, a nodal force of
17500Kn in the X direction and -3500kN in the Y direction can also be seen throughout.
The second topology is designed to exploit a fluctuating ply angle distribution of the blades
span with reference to different sections. Each section of the blade possesses a variable ply
angle including increasing and decreasing ply angles. Specifically, four sets of decreasing ply
angle data (tables 11-14) ranging from 85-65 down to 70-50 contributions. Like topology one,
the induced twist values are tabulated at each airfoil within its span accounting for 5 sections
per layup. These results show a clear increasing in induced with a decreasing ply angle
spanning the blade. In addition to this, the maximum deformation of the blade also shows an
progression of 0.3845 metres with decreasing ply angles. Graphical representations are used
comparing the induced twist at each section vs the blades span at the relating section; this is
done for each separate case. Graphs 10-13 represent a clear increase in induced twist β value
throughout the blades span with a decreasing ply angle distribution.
Conversely, four data sets of increasing statistics can be found (tables 15-18). These are also
implemented to highlight the correlation between varying ply angles and the induced twist β
value. In contrast to the decreasing ply angle setup, the increasing ply angle configuration
shows a decreasing induced twist β value as the ply angle increments upwards as shown in
Graphs 14-17 where induced twist β value for each section of the blade is plotted against the
blades span.
47. 47
9.0 Conclusion
Evidently, a suitably configured blade incorporating a viable elastic coupling configuration
plays a vital role in maximizing overall turbine efficiency, more precisely, as seen from the
research and calculations conduced above, a lower ply angle configuration produces a
higher induced twist angle. Conclusively, statistics above shows almost two degrees
difference between a fully uniform blade configuration and an increasing ply angle layup.
In turn the resultant higher β value offers a two degree difference which can contribute to a
more reliable, sustainable and energy efficient turbine assembly. Equally, a poorly
configured blade can contribute to higher lift and drag co-efficient resulting in stall; a poor
aerodynamic profile drastically impacts performance and hinders turbine productivity.
As mentioned, The FEA based simulation method has made the design of BTAB’s
practical. Vast amounts of physical man hours, materials and resources are saved due to
software developments, whilst not perfected; such design tools are proficient in offering
virtually valid simulations that still can be applied. Unfortunately, to achieve a fully
applicable model, various other design constrains are involved which current software isn’t
capable of recreating, due to this; all results established are purely theoretical. Ultimately,
crucial constraints have to be assumed, or estimated making the FEA of the blade
inefficient and lacking validity for real life application.
48. 48
10.0 Recommendation for further work
For the purpose of this paper, the potential forces impacting upon the blades structure was
being simulated via a nodal force applied to along the blades span. Realistically, this
discrepancy applies a constant force in one direction, not accounting for varying wind
velocities and angle of attack of incoming forces, effectively, not applicable for a real life
situation. Ideally, a programme competent in accurately recreating wind flow would be
better suited and offer a more practical outcome.
Unfortunately, software is entirely dependent on the ability of the operator. Such a
complex blade with many variables would require a fully trained candidate capable of
manipulating the blades constraints in order to maximize software capabilities.
A meshing strategy could be implemented in order to define the blades entities and
ultimately contribute to the accuracy in which ANSYS can form results. However, a more
refined mesh requires additional computation power and impacts the speed and capabilities
of the software. Ideally, a smaller mesh sizing could be implemented to contribute to a
more accurate profile.
49. 49
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ANSYS – Acp Pre material setup configuration
ANSYS – fixed support
55. 55
ANSYS – Nodal Force
ANSYS – Solution, directional deformations of LE and TE at each section.
56. 56
Appendix B: Energy production associated with a wind turbine blade
Appendix C : Induced Twist; single-step (SS) and coupled aero structure (CAS)
simulation [21]
Appendix D: Tip induced twist [22]
57. 57
Appendix E: Tip induced twist. FEA based and non-FEA-based CAS simulations [23]
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