Comparative Study and Design of Custom Wind Augmentation Shroud

This report presents a comparative study and design analysis of custom-constructed wind augmentation shrouds aimed at improving the efficiency of wind power output. The introduction highlights the importance of alternative energy sources, particularly wind energy, and the limitations of current ...Read More

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A COMPARATIVE STUDY AND DESIGN OF CUSTOM CONSTRUCTED WIND
AUGMENTATION SHROUD TO IMPROVE EFFICIENCY OF POWER OUTPUT

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Introduction
Alternative sources of energy are vital for application of efficient power sources
in the future. The other sources such as fossil fuel are reducing at a very high rate and
causing issues such as environmental degradation and global warming. Creation of
better ways of generating energy as well as utilising renewable and clean energy should
be highly invested on. Among others, innovations in wind energy have been developing
rapidly and are expected to play a fundamental role in the field of energy (Isensee &
Abdul, 2012). However, a comparative study between the rate of using wind power and
the overall demand for energy is still subtle especially the level of development is
negligible in the remote area.
Remote areas suitable for the development of wind power plants, complex
terrains and the turbulent nature of the local winds are affecting the installation of wind
turbines. Therefore, the introduction of new and innovative wind energy systems that
produce high output regardless of the wind speed and patterns are desired.
It is imperative to better understand various ways of improving the efficiency of
wind turbines, as well as bringing down the cost to an economical level. The cost of oil
and other non-renewable resources are on the rise every day (Carroll, 2014). Improving
the efficiency of wind turbines helps in reducing the energy limits being experienced
today. In the future, turbines will be able to harness more energy from the wind with
limited technological improvements.
A considerable number of high-efficiency turbines lowers the cost of energy as well
as generate power at a lower cost. Wind shroud system is one of the major techniques
that can be utilized to improve the efficiency of the turbines. The wind shroud systems
have a duct that surrounds the blades that increases the cross-sectional area of flowing

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wind. The resultant sub atmospheric pressure within the duct draws more air through
the turbine blades and hence providing more power to be generated compared to the
traditional turbines (Bet & Grassman, 2013).
Generation of wind power is proportional to the speed of wind cubed(Phillips,
2003). Therefore, an increase in output is caused by the possibility to increase the speed
of the wind and using the wind fluid dynamic around the structure, the output of power
of the wind turbines can be increased considerably. Even though there have been some
studies on shrouded wind systems reported, it has not provided attractive subjects
conventionally. Specific research conducted extensively is the examination of shrouded
wind turbines by Çetin, Yurdusev, Ata, & Ozdamar (2006).
In most of the recent studies, the focus concentrated on the techniques used to
concentrate wind in the duct with a wide open angle, and a boundary segment
controlled with a number of flow slots is used in order to concentrate the flow that goes
inside the surface of the duct. Therefore, the technique of using boundary segments
reduces the loss of pressure through flow separation and increasing the mass flow
within the conduit.
Based on this concept, a company in New Zealand developed the Vortex 7 diffuser
augmentation turbine (Abe, at al., 2006). They utilized a slotted duct that would help
prevent separation within the duct. Additionally, they built a ring profiled structure in
the wide opening of the turbine. It was reported that the new modified structure
increased Power output due to the wing system by a factor of 1.8 compared to the bare
turbines (Abe, at al., 2006). Even though there have been, other ideas being reported,
most of them are yet to reach commercialization.

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The primary objective of the present study concerning developing a wind system
with higher output is determining the best way to harness wind energy in a more
efficient way as well as the right shroud that can be used to generate energy more
efficiently. As an alternative, the shrouded wind system technology might provide
energy to areas with turbulent wind patterns as well as other remote areas, where
electricity is yet to be installed. In fact, shrouded wind systems are an attractive
alternative for the developing market especially for areas that lack electricity or areas
with energy deficiency.
Shrouded wind systems have many advantages over the bare turbines. The newly
innovated turbines are easy to install since they have a shorter construction period that
extending the utility grid line. This turbine technology has been reported to be lesser
complex to construct (Hirahara, Hossain, Kawahashi & Nonomura, 2005). As for the
reasons, local manufacturing is usually a preferred option in remote areas or developing
areas that could, in turn, boost economic development as well as reducing the cost of
production.
This model of turbine technology would also increase the wind velocity through the
blades which include small inlet shroud and a diffuser. A low-pressure area is usually
generated behind the diffuser as vortices are created. Not only there is a huge
development in the wind industry in regard to power production through the wind
turbines, but also on the effectiveness of the turbines used. Recent research shows that
researcher is looking for much better ways of improving and increasing the
effectiveness and applicability of the present wind turbines (Hirahara, et al., 2006)

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Literature Review
Shrouded Wind turbines are newly developed wind turbine system that not only
utilizes a diffusing structure but also a large flanged structure that was developed by
Ohio, Karasudani, and Inoue (2008), from Kyushu University, Japan. The research
conducted by Ohio karasudani in 2011 reported that the Shrouded wind system was
increasing the power augmentation by a factor of about 5, in a given wind speed and the
diameter of the wind turbine (Ohya & Karasudani, 2012).
A simulation result conducted by Bet and Grossman (2003) has reported a
substantial increase in coverage of low-pressure areas behind the turbine. Along with
the studies above, this section will present the main theories for the assessment of
shrouded wind turbine as compared to the bare turbine for turbine aerodynamic
evaluation.A preliminary review of the literature is made to understand the fundamental
concepts of the Shrouded wind turbines. Some of the key contributions made by
researchers in the field in the past few years will be discussed.
The invention of accurate models of aerodynamic aspects of wind turbines is one
significant way of analysing different wind energy systems. The operation of wind
turbines induces phenomena like wind flow components where the direction and the
magnitude of the wind are the rotor changes and the turbine blades rotate (Cetin,
Yurudusev, Ata & Ozdamar, 2005). Furthermore, wind flow separation becomes more
complicated in the new model. Theinstabilities of the wind interacting with the blades,
hub and the tip of the vortices impact the character of the entire flow. The aerodynamics
of the wind turbines becomes more complex with all the wind instabilities as well as
flow interaction. (Burton, Sharpe, Jenkins & Bossanyi, 2001).

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First, in order to understand the complex physics and aerodynamic used in
developing the shrouded wind turbines one must analyse and understand a simple one-
dimensional model (Archer & Caldeira, 2009). To understand the concept of the
shrouded rotor, it is also important to examine the theoretical concept which governs
the performance of shrouded wind turbines.
According to the Augmentation ratio ra, it is easy to describe the enhanced energy
produced by the turbines combined by the diffuser. Thus, the augmentation ratio is
expressed as (Aranake, Lakshminarayan & Duraisamy, 2013): ra= (Cp, d)/0.593, these
Cp,d represents the power coefficient for a turbine with the diffuser.
Shrouded Wind turbines can combine various systems to assist in concentrating and
accelerating the wind. A hollow structure is used for surrounding the turbine as a way
of enhancing the flow of wind. Applying a nozzle in a converging shape at the inlet of
the shrouded wind system is beneficial especially in turbulent wind flow condition,
which is common in urban areas (Hirahara, et al., 2005).
The shrouded turbines exploit the venturi effect, where a reduction in pressure of the
wind and the velocity of wind are produced by the passage of the fluid in a contraction.
For a shrouded wind system, contraction is performed by the shroud surrounding the
turbines (Isensee, et al., 2012). At the nozzle section, the diameter of the inlet should be
larger than the outlet in order to lower the wind velocity. Also, in regards to the outlet,
the velocity is increased due to a decrease in the area (Vermillion, Grunnagle, Lim &
Kolmanovsky, 2014).
Albert Betz, a German physicist calculated that no wind turbine could convert more
than 59.3% of the kinetic energy of the wind into mechanical energy turning a rotor.
This is known as the Betz Limit, and is the theoretical maximum coefficient of power

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for any wind turbine. In a bare wind turbines operating at a maximum Betz limit, the
flow of air decreases to approximately 2/3 of the velocity of the free stream. This
decrease in airflow causes an increase in pressure in front of the rotor inducing a small
section of the mass flow being pushed around the rotor (Khunthongjan & Janyalertadun,
2012).
A way of increasing the flow of air can be incorporated by using an annular lifting
device around the turbine. This device is what is known as a shroud. The increase in the
exit plane of the shroud together with a reduction in the exit pressure enhances the mass
flow leading to higher extraction of energy.
The philosophy behind a flange at the exit of the shroud diffuser is to create a low-
pressure system at the downstream to increase the velocity of incoming air. Past
research conducted on the flange diffuser only focused on the impact of the width of the
vertical Fringe (Carroll, 2014).
Grady & Hader (2012) developed a diffuser to a bare wind turbine so as to increase
the efficiency of the wind turbine and also conducted an analysis of the fluid flow. The
outcomes of the simulation indicate that there was an increase in velocity of the wind by
approximately 60% (Isensee, et al., 2012).
Toya, Kusakabe & Yuji (2007) developed a convergent and a divergent shroud wind
system using an ansys. Later analysis of the wind flow was conducted on the turbine
with a shroud and a bare turbine. The outcome showed that the output of the turbine
with a shroud increases three times compared with the one with no turbine (Toya, et al.,
2007).

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References
Archer, C. L., &Caldeira, K. (2009). Global assessment of high-altitude wind power.
Energies, 2(2), 307-319.
Aranake, A. C., Lakshminarayan, V. K., &Duraisamy, K. (2013, January). Computational
analysis of shrouded wind turbine configurations. In 51st AIAA Aerospace Sciences
Meeting including the New Horizons Forum and Aerospace Exposition (pp. 07-10).
Abe, K., Kihara, H., Sakurai, A., Wada, E., Sato, K., Nishida, M., &Ohya, Y. (2006). An
experimental study of tip-vortex structures behind a small wind turbine with a flanged
diffuser. Wind and Structures, 9(5), 413-417.
Bet, F., & Grassman, H. (2003). Upgrading conventional wind turbines.
Renewable Energy, 28, 71-73.
Burton, T., Sharpe, D., Jenkins, N., & Bossanyi, E. (2001). Wind energy handbook. John
Wiley & Sons.
Carroll, J. (2014). Diffuser augmented wind turbine analysis code (Doctoral dissertation,
University of Kansas).
Çetin, N. S., Yurdusev, M. A., Ata, R., & Özdamar, A. (2005). Assessment of optimum tip
speed ratio of wind turbines. Mathematical and Computational Applications, 10(1),
147-154.

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Hirahara, H., Hossain, M. Z., Kawahashi, M., & Nonomura, Y. (2005). Testing basic
performance of a very small wind turbine designed for multi-purposes. Renewable
energy, 30(8), 1279-1297.
Isensee, G. M., & Abdul-Razzak, H. (2012). Modeling and analysis of diffuser augmented
wind turbine. International Journal of Energy Science, 2(3).
Khunthongjan, P., & Janyalertadun, A. (2012). A study of diffuser angle effect on ducted
water current turbine performance using CFD. aa, 100(4), 1.
Ohya, Y., & Karasudani, T. (2010). A Shrouded Wind Turbine Generating High Output
Power
Ohya, Y., Karasudani, T., Sakurai, A., Abe, K., Inoue, M., 2008. Development of a
shrouded wind turbine with flanged diffuser. J. Wind Eng. and Ind. Aero. 96:
524-539.
Ohya Y, Karasudani T., (2012). A shrouded wind turbine generating high output power.
Energies, 3(4):634–649.
Phillips, D. J. (2003). An investigation on diffuser augmented wind turbine design (Doctoral
dissertation, The University of Auckland).

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Toya, H., Kusakabe, T., & Yuji, T. (2007, October). Fluid flow analysis and design of a
shroud for wind turbine using ANSYS. In Electrical Machines and Systems, 2007.
ICEMS. International Conference on (pp. 298-301). IEEE.
Vermillion, C., Grunnagle, T., Lim, R., & Kolmanovsky, I. (2014). Model-based plant design
and hierarchical control of a prototype lighter-than-air wind energy system, with
experimental flight test results. IEEE Transactions on Control Systems Technology,
22(2), 531-542.