Study the Effect Diffuser Length and Degree
to Horizontal Wind Turbine
Fatahul Arifin
1,2
, R. D. Kusumanto
2,3
, Yohandri Bow
2
, Rusdianasari
2
, Ahmad Taqwa
2
,
Afries Susandi
2
, Yusuf Dewantoro Herlambang
4
, Min Wen Wang
5
and Carlos R. Sitompul
3
1
Department of Mechanical Engineering, Politeknik Negeri Sriwijaya, Jalan Srijaya Negara, Palembang, Indonesia
2
Department of Renewable Energy Engineering, Politeknik Negeri Sriwijaya, Jalan Srijaya Negara, Palembang, Indonesia
3
Department of Electrical, Politeknik Negeri Sriwijaya, Jalan Srijaya Negara, Palembang, Indonesia
4
Department of Mechanical Engineering, Politeknik Negeri Semarang, Jl. Prof. Sudarto, Semarang, Indonesia
5
Department of Mechanical Engineering, National Kaohsiung University Science and Technology,
No. 415, Jiangong Rd., Kaohsiung, Taiwan
Keywords: Diffuser, Wind Energy, Length, Angle, Power.
Abstract: Nowadays, Diffuser Augmented Wind Turbine (DAWT) has been used to improve wind turbine use in a low
wind speed area by directing the wind speed. The technology is the pressure difference between inside and
outside of DAWT, which is occurred. So, it increases the velocity of wind, and the power enhance as well.
The software ANSYS was conducted to examine this study. The variation diffuser length (L) and angle were
in range 0.5D-1.25D and the range 4
o
-16
o
. Experiments were also carried out under 3 conditions: wind turbine
only, DAWT (L=0.5D) at 8
o
diffuser angle, and DAWT at 12
o
diffuser angle to observe voltage and electric
current, power generated, and rotor rotation. The results show that installing a diffuser with a certain length
and angle increases the power generated by 1.6-2.1 times higher than without a diffuser.
1 INTRODUCTION
The national and global energy problem is the rising
cost of fossil energy; coal, gas, and oil. Naturally,
energy prices will continue to increase, along with the
accumulative scarcity of non-renewable energy
sources and the rising demand for energy (
Ploetz,et. al
2016).
Presently Wind turbine industry is becoming one
alternative for energy production. In the financial
aspect, the wind industry shows very intense
progress, which is expected to participate in fossil
fuel energy generation this decade.
On the topic of the importance of the turbine blade
in its energy generation, lots of research has been
developed to make the blade more efficient. Nicolette
Arnalda Cencelli optimized a designed blade. In this
research, some airfoils. They created the airfoil by
using Xfoil software for different sections, then
theresult showed new airfoils could increase the
output power (
Mohammadi, et. al 2016). The influence
of the air density variation with altitude on the
performance of a small horizontal axis wind turbine
blade was studied by Pourajabian et al. (2014). Sharifi
and Nobari studied in optimization of pitch angle
along with wind turbine blades, based on a coding of
aerodynamic. They obtained a coding of aerodynamic
that could accurately predict the aerodynamics of
horizontal axis wind turbines (Sharifi and Nobari.
2013). The type of vertical turbine strongly
influenced by the swept area. The swept area affected
drag and lift force, and then they applied dimensional
engineering to obtain the optimal performance of the
wind turbine (Yuliandi, et. al. 2021).
Diffuser Augmented Wind Turbine (DAWT) can
be a favorable solution to solve those problems by
adding a shroud to the turbine in increasing the wind
turbine power output. The diffuser's working
principle is to result in a pressure difference between
the inside and outside the diffuser. This technology
has developed in the early 1950s. These theoretical
results were presented on small-scale wind turbines
with shroud and increased power by 4% compared to
lacking shroud in wind turbines (
Putra, et. al 2018). The
wind velocity profile around the diffuser, which
Arifin, F., Kusumanto, R., Bow, Y., Rusdianasari, ., Taqwa, A., Susandi, A., Herlambang, Y., Wang, M. and Sitompul, C.
Study the Effect Diffuser Length and Degree to Horizontal Wind Turbine.
DOI: 10.5220/0010951000003260
In Proceedings of the 4th International Conference on Applied Science and Technology on Engineering Science (iCAST-ES 2021), pages 681-685
ISBN: 978-989-758-615-6; ISSN: 2975-8246
Copyright
c
 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)
681

previously modified the diffuser in the form of
additional inlet and flange curvature, had been
studied by Putra, et. al. (2018).
Many researchers used the software to solve the
design of the wind turbine. Susandi et al. studied
Diffuser Parameters in the Performance of Horizontal
Axis Wind Turbine using Computational Fluid
Dynamics using Ansys software (Susandi et.al.
2021). Garmana et al. used the solid work software to
investigate the combination of Savonius and Darrieus
Turbine with differences in the Number of Savonius
Turbine Blades (Germana et. al. 2021). Paranjape et
al. (2020) studied the various designs, experiments,
and CFD simulations of wind deflectors on Savonius
wind turbine type using CFD software then concluded
that installing a flat-plate deflector in the Savonius
turbine can increase the power coefficient by 27%.
This study aims to analyze the performance of a
horizontal axis wind turbine by applying variations in
the length and angle of the diffuser.
2 METHODOLOGY
The design of the diffuser geometry is illustrated in
Figure 1 (a). The design HAW turbine with and
without a diffuser is shown in Figure 1 (b). The wind
blows to the turbine entering through a diffuser with
a smaller inlet cross-section than the outlet section.
Formula 1 shows the calculation of the amount of
power generated in the diffuser based on density,
area, and velocity (
Bussel. (2007).
𝑃=
1
2
𝐴
𝜌 𝑣

𝐶𝑝
(1)
where P is power (W), ρ is air density (1.225 kg/m3),
A is turbine swept area (m2), and v is wind velocity
(m/s)3, and Cp is power coefficient. In this paper, Cp
= 0.59 is the maximum value theoretically for the wind
turbine, which is called the Betz Limit (Spera 2009).
Figure 1: (a) Design Diffuser (b) Design of wind turbine
with and without Diffuser.
The generator, measuring equipment, panel boxes,
lights, sensors, and electrical installation is placed in
the tower. The output of the wind generator is
measured with voltage and current metering.
Furthermore, the wind generator output is converted
from Alternating Current (AC) to Direct Current (DC)
through the Wind Charge Controller. The output of the
Wind Charge Controller will supply the battery and
LED lights. The voltage and current of the LED lamps
are measured using a meter (power data logger). RPM
on the wind generator is calculated using an RPM
sensor that reads the rotation of the wind generator.
The design of a horizontal axis wind turbine equipped
with measuring tools can be seen in Figure 2.
Figure 2: Structural Design of DHAW Turbine.
The study steps are reviewing the literature, running
CFD simulation, designing and manufacturing wind
turbines, finally collecting data. The flowchart of the
study can be seen in Fig 3.
3 RESULT AND DISCUSSION
3.1 CFD Analysis Results
According to the result of running CFD, Ansys
applied in this research with a magnitude velocity of
5 m/s. Then, the diffuser angles were changed 4
o
, 8
o
,
12
o
, 16
o,
and the L = 0.5D to 2.5D while D = 1200
mm. The result is shown that the optimum diffuser
angles are 8
o
to 16
o,
and the length is 0.25D to 1.25D
(Susandi, et al 2021).
As shown in Figure 4, the wind enters the diffuser
with the high velocity and then out the diffuser with
low velocity. The best profile velocity contour can be
obtained at a higher diffuser angle, and then the
iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science
682

diffuser length gave an excellent performance from
0.5D until 1.25D.
Figure 3. Research Flow chart.
Figure 4: CFD of Ansys Fluent Simulation for Diffuser
Length 0.5D to 1.25D angle 4
o
to 16
o
.
3.2 Comparison of the Power
Generated in Theory and
Experiment Results
Based on theories and experiments, it is possible to
compare the power generated in the turbine without
and with a diffuser. The values for calculating turbine
power in theory and their comparison with turbine
power experimentally can be seen in Figs. 5 – 7. It can
be observed that by theory, there is an increase in
power (P
Augmented
) in the wind speed range of 1-5.5 m/s
for each diffuser angle compared to the power of a
horizontal axis wind turbine without a diffuser is 1.3-
1.4 times. A diffuser with a length of L=0.5D and an
angle of 8
o
can simulate an increase in turbine power
of about 1.3 times.
Meanwhile, a diffuser with a length of L=0.5D and
an angle of 12° can increase power up to 1.4 times.
When compared to the power generated by theory and
experiment in Figs. 5 -7 shows that the power
generated by the approach is greater than the power
induced experimentally. For example, at a wind speed
of 3.5 m/s DAWT 12
o
, the Theory is 21.74 Watts,
while the Experiment is 1.96 Watts.
The power generated in this theory is the available
power from the wind turbine. The electrical power
induced experimentally will be smaller than the
available wind power. This is influenced by many
factors, including the friction factor in the turbine,
transmission efficiency, and generator efficiency,
which causes the power generated by the system to be
lower. It can be seen in Figures. 5 - 7 that the wind
speed is directly proportional to the electrical power
produced, meaning that the increase in wind speed
and the electrical power generated are increasing.
Figure 5: Power Generate by HAWT (Without Diffuser)
Theory and Experiment.
Study the Effect Diffuser Length and Degree to Horizontal Wind Turbine
683

Figure 6: Power Generate by Wind Turbine with Diffuser
8
o
.
Figure 7: Power Generate by Wind Turbine with Diffuser
12
o
.
This is inseparable from the rotation. The increase
in rotation of the turbine is in line with the increase in
rotation of the generator. When the generator shaft
starts to rotate, there will be a change in flux in the
stator. Eventually, this flux change will produce a
particular voltage and current whose value is directly
proportional to the wind speed. This is also by the
Betz Limit, which states that the maximum energy
that can be converted is about 59% of the total kinetic
energy of the wind and is commonly known as the
power coefficient (Cp).
As can be seen in Table 1, the average
enhancement of Turbine power theory is 1.3 for
DAWT 8
o
and 1.4 for DWAT 12
o
higher than without
diffuser, while in Table 2, the moderate enhancement
of Turbine power experiment is 1.602 for DAWT 8
o
and 2.163 for DWAT 12
o
higher than without diffuser.
Table 1: The average enhancement of turbine power in
theory.
Wind Speed
(m/s)
Turbine
power without
diffuser
(Watt)
Turbine
Power
with
DAWT 8
o
(Watt)
Turbine
Power
with
DAWT
12
o
(Watt)
1.0-2.5 2.011 4.042
4.334
2.6-3.5 10.894 14.739 14.561
3.6-4.5 23.375 32.829
33.479
4.6-5.5 43.950 55.139
60.834
Average 20.057 26.687 28.302
(P
diffuser
/P
tanpa diffuser)
Average 1.3 1.4
Table 2: The average enhancement of turbine power in
experiment.
Wind
Speed
(m/s)
Turbine power
without
diffuser (Watt)
Turbine
Power
with
DAWT 8
o
(Watt)
Turbine
Power
with
DAWT
12
o
(Watt)
1.0-2.5 0.460 0.816 0.961
2.6-3.5 0.783 1.188 1.442
3.6-4.5 1.069 1.335 2.201
4.6-5.5 1.300 2.449 3.210
Average 0.903 1.447 1.954
(P
diffuser
/P
tanpa diffuser
) Average
1.602 2.163
4 CONCLUSIONS
The simulation results show that the length of the
diffuser gives a better effect on the performance of
the wind turbine, namely the length of the diffuser L
is 0.25D to 1.25D, and the angle of the diffuser angle
is 8
o
to 16
o
.
The experiments were carried out on 3 wind
turbine conditions, namely on wind turbines only
(without using a diffuser), a diffuser with a diffuser
length of L=0.5D, and a diffuser angle of 8°, and a
diffuser with a diffuser length of L=0.5D and a
diffuser angle. 12°. Experimental data and graphs
show the wind speed dramatically affects the voltage
and electric current generated. If the wind speed is
higher, voltage and electric current generated will be
higher too. Be higher. The effect of installing a
diffuser with a certain length and angle can increase
the power generated by the wind turbine. The ratio of
enhancement of the power of a diffuser wind turbine
to a wind turbine without a diffuser is 1.6-2.1 times.
iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science
684

ACKNOWLEDGEMENTS
This work was supported by Minister of Education,
Culture, Research and Technology Republic
Indonesia, Politeknik Negeri Sriwijaya. The financial
support is acknowledged,
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