International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Special Issue 3, February 2014)
International Conference on Trends in Mechanical, Aeronautical, Computer, Civil, Electrical and Electronics
Engineering (ICMACE14)
Aerodynamic Optimization of Wind Turbine Blade by
Employment of Slot to Counteract the Effect of Drag
B.Subash1, C.Nithyapathi2, Dhivya Manikandan3, Murali.K.K4
1
PG student, M.E.Aeronautical Engineering, Karpagam University, Coimbatore, Tamil Nadu, India
Asst Professor, Department of Aeronautical Engineering, Karpagam University, Coimbatore, Tamil Nadu, India
3
UG student, B.E.Aeronautical Engineering, Nehru Institute of Technology, Coimbatore, Tamil Nadu, India
4
UG student, B.E.Aeronautical Engineering, Nehru Institute of Technology, Coimbatore, Tamil Nadu, India
2
1
[email protected]
[email protected]
3
[email protected]
4
[email protected]
2
Abstract— This document encompasses the results of the
work carried out to check the applicability of the
employment of slots in wind turbine blade. The work of
the authors pertains to the practical implications of the
amalgamation of aircraft and wind turbine aerodynamics.
The slot mechanism which is used in aircraft as a high lift
device can also be employed for the augmentation of the
performance of the wind turbine blade. This is due to the
fact that aircraft and wind turbine operate on the same
underlying basic fundamentals o aerodynamics. This
paper elucidates the implications of the employment of the
slot in a wind turbine blade by means of results obtained
from the use of software whose operation is based upon
the principle of computational fluid dynamics. The results
obtained serve as a beginning for the foray of aerodynamic
control surfaces and high lift devices in wind turbine
design to increase their performance.
Keywords— Air jet vortex generators (AJVG), blade,
boundary layer separation, CFD, dynamic control, LENS,
RANS, static control, slots, wind turbine.
I. INTRODUCTION
The current need of the hour is renewable energy. Renewable
energy is in demand because of the large scale abundance and
absence of harmful pollutants during the process of generation
of energy. Compared to other forms of renewable energy,
Wind energy is the most efficient and appropriate production
of renewable energy. But it does suffer from shortcomings.
The areas of research in wind turbines are in the fields of
aerodynamics, wind turbine tower structures, materials. This
project lies in the domain of wind turbine aerodynamics,
where it deals with the problem of boundary layer separation
in wind turbine blades. The boundary layer separation leads to
the stalling
of the wind turbine blades which results in the reduction of
performance of the wind turbine. This project follows from
the earlier work conducted in Air jet vortex generators
(AJVG) and aims to create a more viable and efficient means
of control of boundary layer separation, meanwhile optimizing
power generation and power control.
II. BASICS OF WIND TURBINE AERODYNAMICS
The wind turbine blade is basically an airfoil in essence.
Hence the wind turbine has to experience the same
aerodynamic forces acting on airfoil. The aerodynamic force
acting on the wind turbine blade is split into two components.
The vertical component is the Lift force, L and the horizontal
component of the force is the drag. While the lift force aids in
the lift off and flight of the aircraft, in a wind turbine the lift
force aids in the rotary motion of the wind turbine blade.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Special Issue 3, February 2014)
International Conference on Trends in Mechanical, Aeronautical, Computer, Civil, Electrical and Electronics Engineering
(ICMACE14)
The lift force also contributes the required force to
overcome the drag.
Fig 1 Wind turbine blade aerodynamics
The lift force hence is responsible for the power production
by the wind turbine. The wind turbine efficiency hence
implies heavily upon the production of lift and conversely
factors affecting lift production also affect the production of
power by the wind turbine. One of the main factors affecting
lift production is boundary layer separation.
The boundary is classified into laminar and turbulent
boundary regions in the flow. The turbulent boundary layer is
the region that is directly responsible for boundary layer
separation. The laminar region of boundary layer is
characterised by the presence of streamlined flow. The flow
separation affects the lift force highly and also serves to be
detrimental to the flow regimen by contributing to the increase
in drag.
III. PROBLEM DEFINITION
The boundary layer is defined as the layer of flow that
attaches itself to the surface of the body under consideration
due to its viscous properties and hence the velocity at the
surface will be zero. This region of flow that remains
stationery at the surface and attaches itself to the body is
termed as boundary layer. As previously mentioned the
boundary layer is divided into laminar and turbulent regions
and this demarcation is denoted by means of the transition
point. The transition from laminar to turbulent region in a
boundary layer cannot be avoided but can be postponed.
This elongation of the position of the transition point
ensures that majority of the flow region in the boundary layer
is laminar and hence the layers of flow adjacent to the
boundary layer also achieve a streamlined path for the
majority of the flow.
The boundary layer hence affects the entire flow and hence
the aerodynamic force that generates due the flow body
interaction. In aircraft there are many techniques employed to
control boundary layer separation of which slots are a highly
beneficial design concept. The slots serve to equalize the
pressure differential in the span wise flow distribution across
the aircraft wing.
Boundary layer separation also affects the region of flow
around a wind turbine blade. The boundary layer separation is
a major menace to the lift force that is created by the rotary
movement of the blade in the flow. The earlier studies in the
domain of wind turbine aerodynamics were concentrated with
the improvement of the aerodynamic shape of the blade. The
recent studies are concentrated on the control of boundary
layer separation. The recent concept was the employment of
air jet vortex generators.
Air jet vortex generators or AJVGs is a pneumatic
mechanism. The air jet vortex generator is placed on
windward or wind facing side of the wind turbine blade. The
AJVG are basically a series of minute holes on the surface.
The holes are in turn connected to a plenum chamber. The
pneumatic system of AJVG is power driven. During the
operation of the wind turbine the AJVG supply air flow which
results in the creation miniscule vortices in the flow that
passes over the surface of the blade. The air that moves
downstream hence is introduced with vortices that make sure
that the boundary layer separation over the wind turbine blade
is reduced and hence eventually resulting in the creation of
lift.
This method is plagued by the complexity of the design of
incorporation of pneumatic mechanism in the wind turbine
and the increased vibration in the structure resulting from the
operation of the mechanism. The present work of the authors
attempts at combining the basic concept of AJVG with the
simplicity of the design and working of slots that are used in
aircraft in order to augment the performance of the wind
turbines by virtue of reduction of drag and increment of drag
resulting from enhanced control of boundary layer separation.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Special Issue 3, February 2014)
International Conference on Trends in Mechanical, Aeronautical, Computer, Civil, Electrical and Electronics Engineering
(ICMACE14)
IV. METHODOLOGY
The methodology adopted for the present work is focused
on the comparison of the results obtained by the computer
aided analysis of a conventional wind turbine blade with those
of a renewed design of the same blade with the inclusion of
slot in the blade geometry. The results obtained for static
pressure and velocity contours are to be compared for a
conventional wind turbine blade with those of a renewed
design of the same blade with the inclusion of slot in the blade
geometry so that they would present a clear picture of the
aerodynamic performance of the blade in case of alteration of
design. The velocity contours are significant as they serve to
portray the effect of the slot on the boundary layer separation.
V. MODELLING PROCESS
Fig 2 Drafted model of S833 airfoil
C. Creation of three dimensional solid model
The three dimensional model is essential for the analysis
in a computational fluid analysis software. The three
dimensional model is also done by using CATIA V5
The design process of a wind turbine blade concerns with
the selection of airfoil, creation of a drafting of the same and
finally the creation of a three dimensional model of the two
dimensional drafting sketch completes the modelling process.
A. Selection of Airfoil
The airfoil selected for the wind turbine model is obtained
from the database of National renewable Energy Laboratory
which goes by the acronym of NREL. The NREL airfoil is
selected as it is provided for research purposes and the
properties and design constraint are clearly known which
eases the modelling process.
The airfoil selected for the purpose of design for the present
work is S833.
The S833 airfoil belongs to family of thick airfoils. The
design Reynolds number is 4.0e5 and the airfoil can be used
for airfoils having span of 1 to 3 m. It is characterised by high
lift coefficient of 1.10.
Fig 3 Solid model of wind turbine blade from S833 airfoil
B. Drafting
The two dimensional sketch of the airfoil is created by use
of computer aided drafting software. The software used for the
current work is CATIA V5.
Fig 4 Solid model of wind turbine
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Special Issue 3, February 2014)
International Conference on Trends in Mechanical, Aeronautical, Computer, Civil, Electrical and Electronics Engineering
(ICMACE14)
VI. PREPROCESSOR
The solid model is then imported as Inter graphical
exchange support (Igs) format to be used in the computer
aided engineering software. The computer aided engineering
software used is ANSYS FLUENT. This software is based on
the principles of computational fluid dynamics and is highly
suited for the current analysis because the turbine blade
analysed takes into consideration the variation of flow field
variables when placed in the path of the wind flow.
The immediate step after importing the model into the
analysis software is to mesh the model. The meshing process
sets the boundary conditions at the inlet and outlet of the
control volume. The model under study is placed inside the
control volume. The outlet velocity is set at 15m/s as this is
the velocity that has to be encountered in real time conditions.
The use of dynamic mesh is unwarranted but a section of the
control volume is imbibed with rotary mesh as the wind
turbine blade has to rotate in real time conditions.
Fig 6 Static pressure contours of conventional model
Fig 7 Static pressure contours of model with slots introduced.
The introduction of a slot in the conventional design serves
to create a uniform pressure distribution
Fig 5 Meshed model
VII. RESULTS AND CONCLUSION.
The results are obtained after comparison of the
conventional and renewed design.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Special Issue 3, February 2014)
International Conference on Trends in Mechanical, Aeronautical, Computer, Civil, Electrical and Electronics Engineering
(ICMACE14)
Fig 8 Velocity distribution over conventional model
Fig 9 Velocity distribution over model with slots introduced.
The pictorial results obtained show that the
employments of slots in the design augment the performance
of the wind turbine. Further research in this direction will
result in enhancement of performance of wind turbine. Future
work is to be carried out in the structural compensation of the
design due to the introduction of slots.
VIII. REFERENCES
[1] Jang Oh Ma, Amanullah choudary, 2013 Effects of wind speed changes
on wake instability of a wind turbine in a virtual wind tunnel using large
eddy simulation
Journal of Wind engineering and Industrial
Aerodynamics Elsevier
[2] Jang Oh Ma, Amanullah choudary, 2013 Large eddy simulation of the
wind turbine wake characteristics in numerical wind tunnel model
Journal of Wind engineering and Industrial Aerodynamics Elsevier
[3] S.Shun,N.A.Ahmed,
2012
Wind
turbine
performance
improvementsusing active flow control techniques Journal of Wind
engineering and Industrial Aerodynamics Elsevier
[4] Leonardo P. Chamorro,R.E.A. Arndt, F. Sotiropoulos ,2012 Drag
reduction of large wind turbine blades through riblets: Evaluation of
riblet geometry and application strategies Journal of Wind engineering
and Industrial Aerodynamics Elsevier
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