using composite materials for improving wind turbine...

Abstract— Coal, oil and natural gas are the main pillar of

effective industrial progress. Cheap renewable energy is attracting

most countries attention specially the developing countries for filling

the gap between their demand and available sources. Obviously,

shortage of traditional energy sources can be treated using wind

energy.

This paper gives a comprehensive overview of small vertical wind

turbine which suitable for countries have a moderate wind speed. The

wind turbine performance can be improved using composite materials

blades and rotor shaft. Also, corrosion and wear problems can be

treated using light wind turbine rotor and blades manufactured from

composite materials instead of using metal rotor and blades. As well

as, this paper seeks to enhance investigation of theoretical and

experimental results through using a suitable experimental two small

prototypes of vertical wind turbines. The first prototype has a

composite materials blades and shaft while the second prototype has

metal blades and shaft.

Keywords—Wind Turbine, Renewable Energy, Composite

Material, Experimental Prototype.

I. INTRODUCTION

RADITIONAL energy sources as oil can be considered the

major source to meet the world energy needs but quick

depletion of oil are major concern. Clearly, this problem

can be treated using clean renewable energy but improving its

usage needs sufficient time to meet the future challenges [1].

Some developing countries in middle east region have little

bit resources of conventional energies (coal, oil and natural

gas) like Egypt. Moreover, a yearly expenditure of

conventional energy resources increases rapidly in the

developing countries. Developing secondary sources other

than oil as wind energy must be the challenge of these

countries for assuring the sustainability of energy supplies in

the long term. More than 15% of the energy consumed across

the world is produced from the renewable energy as wind,

solar and sea waves [2].

Alternative energy resources as solar, wind and sea waves

energies can fill the gap between the increasing demand and

available energies in countries have poor in conventional

Khaled M. Khader is member of the teaching staff with the Department of

Production Engineering & Mechanical Design, Faculty of Engineering,

University of Menoufia, Shebin El-kom, Menoufia, Egypt. (corresponding

author's phone: 00201223538574 ; fax 0020482235695;e-mail:

[email protected]).

Mamdouh I. Elimy is member of the teaching staff with the Department of

Production Engineering & Mechanical Design, Faculty of Engineering,

University of Menoufia, Shebin El-kom, Menoufia, Egypt. (corresponding

author's phone: 00201097221998 ; fax 0020482235695;e-mail:

[email protected]).

energies. Wind energy can be easily converted into mechanical

energy using wind turbines. These wind turbines are classified

into two groups, horizontal (HAWT) and vertical (VAWT)

wind turbine axes. Structures of horizontal axis wind turbines

are complicated and economically valuable only in areas

having high speed winds throughout day time [3], [4].

Clearly, VAWT has a simple design and low operating and

maintenance costs. Therefore, VAWT suitable for individual

use specially in isolated areas like helping the young farmers

in the desert for producing the electricity or directly driving a

pumps to lift water from the wells. As well as, modeling and

control of a new compressed air energy storage system is

presented for offshore wind turbine in [5].

The vertical wind turbines of savonius blades have many

advantages as the capability to work at low wind speed with a

modest assembly [4], [6]. Many of pervious researches are

dealing with the performance analysis of savonius rotor as [7].

Also, the performance and flow field assessment of a savonius

rotor tested using a wind tunnel in [8].

Electricity can be generated using wind turbine system has

one electric generator coupled to the rotors through a

differential planetary system as presented in [9]. The

requirement of increasing the maximum power which could be

extracted from the air current by using counter rotating wind

turbines introduced in [10].

A new ideas of wind turbine as floating offshore wind

turbine concept introduced in [11], [12]. Also, increasing the

savonius rotors efficiency through a parametric study

presented in [13]. The calculation of the energy production of

wind turbine presented in [14].

Dynamic analysis of a floating wind turbine of vertical axis

presented in [15]. The numerical and analytical study of

vertical axis wind turbine is presented in [16]. Many

researches are dealing with improving the wind turbine

performance using light composite materials for manufacturing

the turbine blades as in [17], [18]. As well as, shaft torsion in

addition to blade bending coupling vibrations in a rotor system

are discussed in [19].

Many researches are dealing with investigation of

theoretical and experimental results through testing an

experimental prototype as [20], [21].

This paper is dealing with improving the wind turbine

performance using light composite materials blades and rotor

(shaft) with a very low corrosion and wear problems. Also, this

paper seeks to enhance investigation of theoretical and

experimental results through using a suitable experimental

small prototypes.

Using Composite Materials for Improving Wind

Turbine Performance

Dr. Khaled M. Khader, Dr. Mamdouh I. Elimy

T

6th International Conference on Trends in Mechanical and Industrial Engineering (ICTMIE'2015) Sept. 13-14, 2015 Dubai (UAE)

7

II. THEORETICAL ANALYSIS OF WIND TURBINE SYSTEM

A wind turbine system consists of flexible blades which

fixed into a torsional shaft as shown in Fig. 1, where, (X1, Y1,

Z1) is the inertia frame coordinate system, coordinate system

(x2, y2, z2) of frame which rotates at a constant speed and

coordinate system (x3, y3, z3) of frame fixed to the blade's root.

Fig. 1 Wind turbine blade system and coordinate sets of

rotating blade deformation

The torsional energies associated with the shaft and disk are

presented in [19] as follows;

tt

I

ZdZ

dSs

IdZT

LS 2

22

12

0

(1)

dZUZ

IGL

s

S

Ss

2

02

1 (2)

Where φ(Z,t) is the torsional displacement with respect to a

continuously rotating (Ω) frame. As well as, Ls, Is, Gs, Js and Id

are the shaft's length, moment of inertia, polar rotary inertia,

torsional rigidity and disk's polar rotary inertia respectively.

Also, the kinetic and strain energies associated with a blade are


dx

dxt

x

tt

vI

vxv

t

vAT

b

b

rb

rdb

bbb

rb

rdbb

22

222

2

2

1

22

1

(3)

dxdxUx

vxrA

xIE

bbb

rb

rdbA

rb

rdbb

2

222

2

4

1

2

1

2

2

(4)

Where, vb is the transvers displacements in y2 direction, IA is

the area moment of inertia about the z3 axis and Ib is the polar

moment of inertia. The displacement of the blade vb(x,t) has

two parts the first one is shaft's torsional displacement φ(Zd,t)

and second one is blade's bending displacement v'b(x,t). The

blade displacement vb(x,t) can be written as follows;

xvzd

bbvtx ',

(5)

Assumed mode method is adopted to discretize the

continuous system in [19] as follows;

tZtZtZi

ii

ns

1

, (6)

NktxVtxVtxkik

iib

nb

v ,.....,2,1,,1

(7)

Where, nb is term of blade and ns is term of shaft are

numbers of modes deemed necessary for required accuracy for

the corresponding subsystems. Also, ηi and ξik are participation

factors. In addition to, Фi and vi are the mode shapes of a

torsional shaft and bending blade. These shapes modes are as

follows;

si

L

ZiZ

2

12sin

(8)

xxxxxv iiiiii coshcossinhsin)( (9)

The following discretized equations of motion in matrix

notation can be formulated through substituting the two

previous equations into the energy expressions and using

Lagrange equations as follows;

02

qKKqM e (10)

Where, [Ke] arising from the elastic deflection dominates at

the low rotational speed. Also, the term -Ω2[K

Ω] results from

rotation, softens the rotor so that it becomes very significant at

high rotational speed which affects the stability of the rotor.

The matrices [M], [Ke] and [K

Ω] are presented in [19]. The

dimensions matrices are (ns+Nd×Nb×nb) × (Nd × Nb × nb)

where, Nd and Nb are the number of disks and blades. The

generalized vector q is;

T

bNdN

T

dN

TT T

q ...........\111

(11)

The solution form q=ceλi is assumed with undetermined

coefficient vector c for useful free vibration analysis where λ

represents the eigenvalue.

Note that, λ is pure imaginary number for most of undamped

rotors, i.e., λ=i ω. Hence;

022

cKKM e (12)

The generalized eigenvalue problem can be expressed as

characteristic equation as follows;

022

KKM e

(13)

The mode shape can be solved using (10) and (13). Hence,

the mode shape can be sketched by substituting the obtained

eigenvalue and eigenvectors into (6) and (7). Table I, indicates

the properties of wind turbines prototype which is shown in

Fig. 2 as follows;

Fig. 2 The design of wind turbine prototype


8

TABLE I

MATERIAL PROPERTIES AND GEOMETRIC OF PROTOTYPES

Through Rotational speed:

Ω 0~300 Hz

Composite

(FRP)

Metal

For Shaft: Young's

modulus: Es, [GPa]

Shear modulus: Gs, [GPa]

Density: ρs, [kg/m3]

Length: Ls&Radius: ds [m]

61.6

0.135

1.381×103

0.6 , 0.019

199.947

76.945

7.850×103

0.6 , 0.019

For Blade: Young's

modulus: Eb, [GPa]

Shear modulus: Gb, [GPa]

Density: ρb, [kg/m3]

Length: Ls&Radius: rt [m]

45.2

0.129

0.49×103

0.4, 0.036

199.947

76.945

7.850×103

0.4, 0.036

For Disk: has same properties as blades

III. SOLUTION VERIFICATION WITH ANSYS

In this study, a finite element analysis software (ANSYS)

employed for constructing the numerical model of assembled

wind turbine and performing modal analyses. The contact

elements supported by the software are arranged in the

interface of the blade, disk and the rotor through constructing

the numerical model. Verification study can be achieved using

refining mesh of the Finite Element (FE) model to guarantee

solution accuracy. The mesh convergence study performed

using static and modal analysis simulations in ANSYS. Static

and modal analysis simulations were chosen regarding wind

turbine blades. The modal analysis observed the convergence

of four modes. Static analysis observed stress at the root of the

blade and its tip as in Fig. 3 which shows system meshes used

to perform the mesh refinement study in ANSYS as follows;

Fig. 3 Mesh Refinements in ANSYS

The proposed design is a vertical axis wind turbine with a

series of alternating polarity magnets mounted at the rotating

shaft. Steady state rotation of the vertical shaft induces a

harmonic vibration in piezoelectric elements through an

alternating attractive/repulsive force between stationary

magnets mounted at the tip of the piezoelectric elements and

rotating, shaft-mounted magnets.

IV. TURBINES POWER'S CALCULATIONS

The equation for calculating the input energy (P) of air

passes through turbine presented in [22], where, energy of the

moving air is the sum of its kinetic energy as follows;

3

2

1VAP

(14)

Where; (ρ) is the air density (1.225 Kg/m3), (V) is the air

velocity and (A) is the swept area which is a function of width

(b) of active blade and its length (L).

As well as, the ideal generated torque (T) of wind turbine

can be calculated using the following from;

PT

(15)

Where, (ω) is the angular speed of the turbine rotor. Also, the

wind speed ratio (ϕ) of turbine is function of the angular speed

(ω), wind speed (V) and radius (rt) of wind turbine. The wind

speed ratio (ϕ) can be written as follows;

V

rt

(16)

Considering the relative velocity over the blades of wind

turbine, the theoretical output power (Pth) of wind turbine


25.0sin5.0 ttth rVrAP (17)

Where (ɵ) denotes the blade position which indicates in Fig. 4

as follows;

Fig. 4 Blades Orientation

Regarding suggested prototype which is indicated in Fig. 2,

right side of wind turbine is non-active side while left side is

active side. Hence, first blade is activating through a range

(0o> ɵ ≥180

o) ,while, the second blade is activating through

(72o ≥ ɵ≥ 180

o). As well as, the third blade through (144

o≥ ɵ≥

180o). Theoretical power coefficient (Cpt) can be written as;

3

2

5.0

5.0sin5.0

VA

rVrA

P

PC ttth

pt

(18)

While, the experimental power coefficient (Cpx) is function

of experimental and input powers (Ptx & P) as follows;

35.0 VA

T

P

PC xtx

px

(19)

Where, (Tx) is the experimental measured torque of prototypes.

V. EXPERIMENTAL VERIFICATIONS

Composite materials blades and shaft of prototype are

manufactured using hand layup method.

A) Composite Shaft, Disk and Blade Preparations:

The rotating composite shaft manufactured with various

types of lamina orientations angles through using the standard


9

procedures of specimens preparation and manufacturing as in

[23]. The composite shaft manufactured with five layers of

(600 mm) long were twisted by the required angle and spread

on die plate at various angles of fibers orientation are

[0/45/0/45/0]. A layer of resin is spread on a die plate treated

by release agent (medical Vaseline). The die plate dimensions

are (1000 mm) long and (19 mm) diameters. As well as, the

composite blade with one random fiber orientation layer of (1

mm) thickness, (400 mm) long and (36.5 mm) radius were

produced.

B) Experimental modal of wind turbine:

The frequency response tests were performed on wind

turbine blade prototype using utilizing fast Fourier transform

dual channel analyzer in conjunction with the computer as

shown in Fig. 5 as follows;

Multi channelanalyzer

Accelerometer

Bearing

Shaft

Blade

Fig. 5 Experimental layout

Dynamic analysis is presented to investigate dynamic Eigen

parameters including natural frequencies, torque and critical

speed of experimental prototype which is shown in Fig. 6.

Fig. 6 Experimental Prototypes

Dealing with, frequency range till 500 Hz, the frequency

response and half power tests were performed for the two loss

factors and the corresponding Eigen frequencies which must

be considered through rotation of turbine, these frequencies

listed in Tables II as follows;

TABLE II

FIRST FOUR NATURAL FREQUENCY IN HZ

Eigen

frequency

Composite wind

turbine Metal wind turbine

FE Experimental FE Experimental

Mode (1)

Mode (2)

Mode (3)

Mode (4)

0.0972

2.8036

5.4654

9.8421

0.09856

2.71241

5.34264

9.62453

0.1195

3.4204

7.2689

11.909

0.10421

3.10245

7.04251

10.9845

Also, Fig. 7 shows an example of measured frequency

response spectrum of composite and metal wind turbine blade

as follows;

Fig. 7 Sample of Frequency Response curve

The resulted vibration response were registered by a

piezoelectric accelerometer mounted at the bearing. As well

as, the accelerometer signals were conditioned in the charge

amplifier in order to fed dual channel signal analyzer.

Analyzer in conjunction with the fast Fourier transform

(FFT) gives the mathematical relationship between time and

frequency successively and displays the frequency response

spectrum (FRS) in addition to registering the coherence

functions with the desired frequency range.

VI. EXPERIMENTAL RESULTS

Fig. 8 shows the relation between frequency and mode

number of two different materials of blades which reveals that

performance of composite materials blade is higher than the

metal one due to the values of flexural elastic modules and

stiffness of these materials, especially at high speed related to

high damping capacity of composite material.

Fig. 8 Effect of material type on frequency at different mode

number

Fig. 9 Input power, output theoretical and experimental power

Experimental output power (Ptx) measured for the composite


10

materials prototype turbine and the metal prototype turbine

thorough measuring the torque (Tx) of prototype turbine and its

rotor angular speed (ω) for different wind speeds (V). These

powers are shown in Fig. 9. Output power of air (P) and

theoretical power (Pth) in addition to the measured power (Ptx)

have a convergence trend at a low and moderate wind speeds

for both composite materials and metal turbines. The relation

between the wind speed ratio (ϕ) and theoretical power

coefficient (Cth) in addition to experimental power coefficient

(Cex) for both composite materials and metal turbines is shown

in Fig. 10 as follows;

Fig. 10 Relation between power coefficients and speed ratio (ϕ)

The experimental power coefficient (Cex) of composite

materials turbine has values higher than experimental power

coefficient of metal turbines at high wind speed ratio.

VII. CONCLUSION

Wind energy can fill the gap between the increasing

demand and available energies in countries have poor in

conventional energies. Wind energy can be converted into

mechanical energy using wind turbines for helping the

farmers in the desert for producing the electricity or directly

driving a pumps to lift water from the wells. Small vertical

wind turbine has attracted most countries attention specially

countries have a moderate wind speeds where, this type of

turbines is suitable for their climate's conditions. This paper is

dealing with this type of turbine which suitable for middle

east countries as Egypt. Also, wind turbine performance can

be improved using composite materials blades and rotor shaft.

In addition to, the corrosion and wear problems can be treated

using light wind turbine rotor and blades manufactured from

composite material instead of using metal rotor and blades.

Experimental results reveal to the improvement of using

the composite materials in manufacturing the wind turbine.

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using composite materials for improving wind turbine...

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