1. Modulation of Vertical Axis Wind Turbine
Apurwa Gokhale1
, Nehali Gosavi2
, Gurpreet Chhabda3
, Vikrant Ghadge4
, Dr. A.P.Kulkarni5
1,2,3,4
Vishwakarma Institute of Information Technology, Pune.
5
Professor, Vishwakarma Institute of Information Technology, Pune.
Abstract— Vertical axis wind turbines (VAWT) are capable of
producing a lot of power, and offer many advantages. The
mechanical power generation equipment can be located at
ground level, which makes for easy maintenance. Also, VAWT
are omni-directional, meaning they do not need to be pointed in
the direction of the wind to produce power.
In recent years more focus is put on the applications of wind
turbines in the urban environment. The modern equivalent
which is based on lift producing blades only exists for 30 years. In
this period airfoils for this application have been developed, but
still much work can be done in this field.
Our main objective is to modify the design to make it self-starting
and to bring it to production stage. The purpose of this project is
easy installation in areas where electricity is not yet available.
optimization of the methodology is achieved for the mass
production of different parts of vertical axis wind turbine. This is
achieved using numerous CATIA models analysed by ANSYS
Workbench.
Index Terms—
S – Swept Area, m2
; R – Radius of rotor m ; L – Length of blade,
m ; Pw – Power available from wind ; Vo – Velocity of the wind,
m/s ; ρ – Air density, kg/m3
; Cp – Power coefficient ; λ – Tip
speed ratio ; ω – Angular speed, rad/s ; σ – Solidity ; N – No. of
blades ; c – Chord length
I. INTRODUCTION
Vertical axis wind turbines (VAWT) are advocated as being
capable of catching the wind from all directions, and do not
need yaw mechanisms and downwind coning. Their electrical
generators can be positioned to the ground, and hence easily
accessible. A disadvantage is that some designs are not self-
starting.
There have been two distinct types of VAWT: The Darrieus
and Savonius types. The Darrieus was researched and
developed extensively by Sandia National Laboratories in the
USA in the 1980’s.
The concept of VAWT can have differently shaped blades. As
the forces of the blades can be large, the ideal blade has a
Troposkien (nearly parabolic) shape with which the
centrifugal force is translated through the blade to the shaft.
This type of blade is mainly used in large turbines and
prevents the blade from failing because of too large rotational
speeds. A large disadvantage is the decreasing radius near the
top and the bottom of the turbine. These parts experience only
low rotational speeds and therefore generate almost no power.
Another concept is the H-Darrieus or Musgrove VAWT. The
blades are straight and therefore the radius is equal over the
total length of the blade, see figure 1.1(b). The power is now
generated over the complete length of the blade. In contrast to
the Troposkien shape blade extra strength is necessary to cope
with the centrifugal forces. The blades can be rotated slightly
to disperse the moment forces on the axis over a larger angle.
The first prototypes of the H-Darrieus were developed in
1986. [2]
The typical VAWT consists of the following parts:
 Supporting mast
 Central Shaft
 Supporting struts for the blades
 Blades
 Generator
The blades of a VAWT have to develop lift and must have
enough thickness to withstand the loads. To achieve this they
have a certain shape, comparable to aircraft wings. This shape
determines how the wind energy is conversed to forces on the
blade. The goal of this study is to develop a new airfoil profile
for an H-Darrieus vertical axis wind turbine. In most of the
existing turbines of this type standard profiles like the NACA
0015 and NACA 0018 are used. These profiles were
developed in the 1930’s by the NACA as standard profile
series for turbulent flow.
II. LITERATURE REVIEW
A. Overview
Horizontal axis wind turbines are typically more efficient at
converting wind energy into electricity than vertical axis wind
turbines. For this reason they have become dominant in the
commercial utility-scale wind power market. However, small
VAWT are more suited to urban areas as they have low noise
level and because of the reduced risk associated with their
slower rates of rotation.
VAWT cost will come down appreciably once they are mass
produced on production line scale. The economic development
and viable use of HAWT would in the future be limited, partly
due to high stress loads on the large blades. It is recognized
that although less efficient, vertical axis wind turbines do not
suffer so much from constantly varying gravitational loads.
VAWT with rated power output of 10 MW could be

2. 3
developed, with at least the same availability as a modern
horizontal axis wind turbine, but at a lower cost per unit of
rated power.
B. How turbines work?
The wind imposes two driving forces on the blades of a
turbine; lift and drag. A force is produced when the wind on
the leeward side of the airfoil must travel a greater distance
than that on the windward side. The wind travelling on the
windward side must travel at a greater speed than the wind
travelling along the leeward side. This difference in velocity
creates a pressure differential. On the leeward side, a low-
pressure area is created, pulling the airfoil in that direction.
This is known as the Bernoulli’s Principle. Lift and drag are
the components of this force vector perpendicular to and
parallel to the apparent or relative wind, respectively.
Fig 1 . Aerodynamic loads on VAWT Blade in terms of lift and drag [5]
C. General parameters considered in design of VAWT [4]
The wind turbine parameters considered in the design process
are:
The swept area limits the volume of air passing by the turbine.
The rotor converts the energy contained in the wind in
rotational movement so as bigger the area, bigger power
output in the same wind conditions.
2. Power and power coefficient
The power available from wind for a vertical axis wind turbine
can be found from the following formula:
Pw = (½)* ρSVo ... (2)
Where Vo is the velocity of the wind [m/s],
ρ is the air density [kg/m3], the reference density used
its standard sea level value (1.204 kg/m3 at 15ºC).
The power the turbine takes from wind is calculated using the
power coefficient:
Cp = (Captured mechanical power by blades / Available power
in wind) ... (3)
Cp value represents the part of the total available power that is
actually taken from wind, which can be understood as its
efficiency.
For small VAWT, the value of maximum power coefficient
has been found to be usually ranging between 0.15 and 0.22.
This power coefficient only considers the mechanical energy
converted directly from wind energy; it does not consider the
mechanical-into-electrical energy conversion, which involves
other parameters like the generator efficiency.
3. Tip Speed Ratio (TSR)
The power coefficient is strongly dependent on tip speed ratio,
defined as the ratio between the tangential speed at blade tip
and the actual wind speed.
 Swept area
 Power and power coefficient
 Tip speed ratio
 Blade chord
 Solidity
 Initial angle of attack
1. Swept Area :
The swept area is the section of air that encloses the turbine
in its movement. The shape of the swept area depends on the
rotor configuration. So the swept area of an HAWT is
circular shaped while for a straight-bladed vertical axis wind
turbine the swept area has a rectangular shape and is
calculated:
S=2RL ... (1)
Where S is the swept area [m2],
R is the rotor radius [m],
L is the blade length [m].
TSR = Tangential Speed at the blade tip / actual wind speed
TSR = λ = Rω / Vo ... (4)
where ω is the angular speed [rad/s],
R the rotor radius [m],
Vo is the ambient wind speed [m/s].
Each rotor design has an optimal tip speed ratio at which the
maximum power extraction is achieved.
4. Blade Chord
The chord is the length between leading edge and trailing edge
of the blade profile. The blade thickness and shape is
determined by the airfoil used, in this case it will be a NACA
airfoil, where the blade curvature and maximum thickness are
defined as percentage of the chord.
5. Solidity
The solidity σ is defined as the ratio between the total blade
area and the projected turbine area. It is an important non

3. dimensional parameter which affects self-starting capabilities
and for straight bladed VAWTs is calculated with,
σ = (N*c)/R ...(5)
where N is the no. of blades,
c is the blade chord (m),
R is the radius of rotor (m).
This formula is not applicable for HAWT as they have
different shape of swept area. Solidity determines when the
assumptions of the momentum models are applicable, and
only when using high σ ≥ 0.4 a self starting turbine is
achieved.
6. Initial Angle of Attack
The initial angle of attack is the angle the blade has regarding
its trajectory, considering negative the angle that locates the
blade’s leading edge inside the circumference described by the
blade path.
D. Comparison and effects of variations in performance
characteristics
There is decrease of aerodynamic performance due to the
increment of rotor solidity. Maximum power coefficient of
VAWT depends on both wind speed and rotor solidity. This is
illustrated in fig below.
Fig 2. Maximum rotor power coefficient as a function of both rotor angular
velocity and wind speed [6]
Following graph shows relation between power coefficient
and tip speed ratio for various diameters of rotor.
From the graph shown below, it can also be observed that the
position of maximum rotor efficiency at (λ~2.4) is roughly
constant. Thus tip speed ratio of 2.4 is selected for calculation.
Fig No. 2.5 : Evolution of rotor power coefficient as a function of the tip
speed ratio [7]
Following graph shows the effect of varying the chord length
on the power captured from the wind. Each line represents a
different chord length with 6 inch producing the highest power
and 1 inch producing the least.
Hence from the graph it is clear that, greater the chord length
greater will be the power output for increasing wing speed.
Hence average chord length of 200 mm is considered for
further design.
Fig 3. Power vs. Wind Speed for Various Cord Lengths (1 inch to 6 inch) [8]
III. DESIGN AND ANALYSIS
A. Design Parameters
Sr.
No.
Name of the
part
Parameter Value
1 - Wind speed (Vo) 4.3 m/s
2 - Density of air (ρ) 1.204 kg/m3
3 - Angular speed
(N)
100 rpm
4 - Radius of rotor
(R)
1000 mm
5 Blade
(NACA0018)
i) Length of blade
(L)
2000 mm
200 mm

4. B. CATIA Model
Various parts of vertical axis wind turbine were designed
using CATIA. Above design parameters were considered for
the same and standard sizes of pipe, nut, bolt, washer etc. were
chosen according to standard catalogues and westerman table.
CATIA models for some of the parts and their final assembly
is shown below.
Fig 4. Catia Model for blades
Fig 7. Assembly of VAWT
C. Material Selection
TABLE.1
Fig 5. Catia Model for centre shaft
ii) Chord Length
7 Rod i) Outer Diameter
ii) Wall Thickness
iii) Length
33.7 mm
4.05 mm
1130 mm
8 Shaft i) Outer Diameter
ii) Wall Thickness
iii) Length
76.1 mm
3.65 mm
440 mm
9 Disc i) Outer Diameter
ii) Thickness
180 mm
3 mm
10 Bolt M16 (Qty-
24)
i) Minor
Diameter
ii) Pitch
13.546 mm
2 mm
11 Nut (Qty-24) Thickness 13 mm
12 Washer (Qty-24) Thickness 3 mm
13 Tower i) Height
ii) Base Area
6000 mm
1500*1500
mm
14 - Swept Area 4*10^6 mm2
15 - Tip Speed Ratio 2.4353
16 - Wind Power 191.4528
Watt
17 - Mechanical
Power
113.453 Watt
18 - Solidity (for 6
blades)
0.6
Fig 6. Catia Model for rods
Sr. No. Part Name Material / Specification
1 Shaft Mild Steel
2 Rods Mild Steel
3 Bolt, Nut, Washer M16 Mild steel
4 Blades Fibre glass

5. D. Analysis of Components
As the material used us mild steel, yield strength is taken as Syt
= 250 N/ mm2.
. Factor of safety was considered to be 2 and
design is modified considering manufacturing aspects.
Analysis of various components was done using ansys
workbench and design was finalised and checked for safety.
Following figures show some of the data of analysis for
various parts.
Fig 9.Equvalent stress on rod
Fig 10.Equivalent stress on bolt
Fig 11. Equivalent stress on Nut
Equivalent stresses on each part are less than the permissible
stresses. Hence the design is safe.
E. Summary of the work
The design of VAWT was finalised and tested on ANSYS.
Factor of safety is 2. Various forces were applied on the parts
and individual part is tested for safety.
Materials were selected by referring previous research
papers. Market survey was done for the same. Further CFD
analysis is to be done in order to confirm design under
dynamic loads and then fabrication will be started. Using 3,4
and 6 blades on the same shaft, the various parameters will be
studied.
REFERENCES
1. The Design and Testing of Airfoils for Application in Small Vertical
Axis Wind Turbines by M.C. Claessens, TUDelft
2. Vertical Axis Wind Turbines: History, Technology and Applications by
Marco D’Ambrosio, Marco Medaglia
3. Small-Scale Vertical +Axis Wind Turbine Design by Javier Castillo,
Tampere University of Applied Sciences
4. Performance Prediction and Dynamic Model Analysis of Vertical Axis
Wind Turbine Blades with Aerodynamically Varied Blade Pitch by
Dhruv Rathi, North Carolina State University
5. Evaluation of the Effect of Rotor Solidity on the Performance of a H-
Darrieus Turbine Adopting a Blade Element-Momentum Algorithm by
G. Bedon, M. Raciti Castelli, E. Benini, World Academy of Science,
Engineering and Technology International Journal of Mechanical,
Aerospace, Industrial, Mechatronic and Manufacturing Engineering
Vol:6, No:9, 2012
6. Effect Of Shaft Diameter On Darrieus Wind Turbine Performance,
Strickland, J. H. (1975) The Darrieus Turbine: A Performance
Prediction Model Using Multiple Streamtube, SAND75-0431.
7. Trade Study: The effect of Cord Length and Taper on Wind Turbine
Blade Design John Larson Group C4: Turbinator Technologies AME
40463 Senior Design
Fig 8. Equivalent stress on shaft