Effect of a Circular Cylinder in Front of Advancing Blade on the...
Transcript of Effect of a Circular Cylinder in Front of Advancing Blade on the...
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 151
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
Effect of a Circular Cylinder in Front of Advancing
Blade on the Savonius Water Turbine by Using
Transient Simulation
Priyo Agus Setiawan1,3*, Triyogi Yuwono1,2, Wawan Aries Widodo1 1Mechanical Engineering Department, Institut Teknologi Sepuluh Nopember
Kampus ITS Keputih-Sukolilo, Surabaya 60111, Indonesia 2Center of Excellence in Automotive Control & System, Institut Teknologi Sepuluh Nopember
Kampus ITS Keputih-Sukolilo, Surabaya 60111, Indonesia 3Marine Engineering Department, Politeknik Perkapalan Negeri Surabaya
Jl. Teknik Kimia Kampus ITS Keputih-Sukolilo, Surabaya 60111, Indonesia *Corresponding Author: [email protected]
Abstract— The paper has investigated the effect of a circular
cylinder diameter on the performance of the vertical axis
savonius water turbine. The free stream velocity over the cylinder
will increase the velocity in the upper side and lower side. The
phenomena will increase the flow momentum when the fluid-flow
through between Savonius turbine and a circular cylinder. The
cylinder can improve positive torque at the advancing blade and
will improve the turbine performance. The flow investigation has
been studied numerically to the Savonius turbine by placing a
circular cylinder as passive control in the front of the advancing
blade side. The paper has seen the influence of the cylinder
diameter variations to the performance and the flow
characteristics of the turbine. The numerical simulation has been
conducted on the Savonius turbine by without and with a circular
cylinder. The numerical of 2D simulation has been conducted by
using a sliding mesh to solve the rotation equipment in the
transient condition and the turbulence model used is the
realizable k-ε (RKE). The firstly, the numerical has been verified
and has validated with respect to experimental data. The data
used in verification and validation is the torque coefficient using
air fluid. Secondly, after the validation has attained, the next
simulation has changed the working fluid to be water by placing
a circular cylinder in front of advancing blade with varying ds/D
of 0.1, 0.3 and 0.5 for each stagger angle () of 0o, 30o, and 60o for
S/D of 0.95. The results have shown that the best performance of
Savonius turbine occurs at the ds/D of 0.5, of 30o, and a TSR of
0.9. The turbine performance has increased by 41.18% higher
than conventional Savonius at of 30o and TSR of 0.9. The ds/D
variations have lowest turbine performance at of 0o.
Index Term— Savonius turbine; circular cylinder diameter;
advancing blade; performance; transient; sliding mesh.
I. INTRODUCTION The ocean current has been conducted measurement of speed
toward average velocity in Indonesian island namely Biawak
Anambas Berhala with the value of 0.272 m/s, 0.055 m/s, 0.135
m/s, and, respectively [1]. Indonesian island has low ocean
currents and is very compatible with the characteristics of the
Savonius turbine having a low tip speed ratio (TSR) compared
to other turbine types. The performance of the Savonius turbine
is lower than to other types of turbine. The study of the Savonius
turbine has been conducted high effort to improve the
performance of the Savonius turbine. The big effort of
improvement toward Savonius turbine has been conducted by
adding obstacle or deflector at advancing blade and returning
blade. Experiment has been conducted in the water tunnel
having dimensions of cross section 0.73 m x 0.33 m. The
turbine model has used the aspect ratio of 0.7. Experiment has
used modified Savonius installed two (2) deflector plates on the
returning blade and advancing blade. The model has used the
free stream velocity of 0.45 m/s with Re of 1.32 x 105.
Experimental results have shown that the maximum coefficient
of power attained at 0.35 and a TSR of 1.08 [2]. The width
curtain variations of the deflector in front of the returning blade
have been conducted numerically. The curtain installed in front
of the returning blade is generally more effective to increase the
performance. But, The results of numerical have shown that the
best performance occurs S/D of 2 has lower than without
curtain or called as conventional Savonius turbine for S/D of 2
at Reynolds number (Re) of 90,000 [3]. The performance of the
turbine has been conducted by using a circular cylinder varying
ds/D of 0.1, 0.3, 0.5, 0.7 and 0.9 installed beside of advancing
blade. The best power coefficient (Cp) has achieved at ds/D =
0.7 and TSR = 0.7 [4]. Modification of the blade has studied
turbine performance numerically comparing the elliptical and
conventional turbine blade. The results showed that the
conventional blade has a lower performance than the elliptical
blade [5]. The experiment has been conducted by combining
two shapes of blades namely concave elliptical and circle-
shaped model from [5] and The power coefficient has improved
up to 11 % compared to the conventional blade at the tip speed
ratio of 0.79 [6]. The next research has been discussed
numerically toward the flow characteristics from [6] using 2D
simulation. The combined blade has been conducted having the
best performance. The visualization has taken velocity and
pressure contour on each blade and the combined blade has
shown the pattern of particular flow giving the best
performance compared to the elliptical blade and conventional
blade models [7]. The flow visualization has been conducted
experimentally in a water tunnel toward the Savonius turbine
with an overlap ratio of 0.23. The visualization flow has been
obtained pattern flow as dragging flow, stagnation flow,
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 152
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
attached flow, overlap flow, vortex flow advancing blade and
vortex flow returning blade [8]. The visualization results will
be applied in this present study although using the conventional
Savonius turbine.
The performance of Savonius has been conducted
experimentally by using the model of Savonius turbine and
tested in the wind tunnel at a velocity of 7 m/s and 14 m/s. The
Savonius model has 1 m of diameter and 1 m of height with the
number of bucket 2 and 3. The experimental also has been
conducted and the overlap ratio has been varied from 0.0 to 2.0.
The best performance occurs on the number of the bucket of 2
and the overlap ratio of 0.1 - 0.15 [9]. The next research of
overlap ratio also has been conducted numerically on the
Savonius turbine. The numerical has been varied by the overlap
ratio of 0, 0.1 and 0.2 and has obtained the maximum torque at
the overlap = 0.2 [10].
The study has been conducted about the tidal stream turbine
to compare the numerically and experimentally. Numerical has
conducted by using 2-D and 3-D simulation by comparing by
experimental. The results has shown that 2D analysis can be
used as a parametric design tool [11]. The turbulence model of
Realizable k – ε (RKE) is suitable as flow prediction tool such
as flows separation, complex secondary flow [12]. The
investigation has used 2D simulation using CFD for Savonius
turbine. The 2D has shown good results or acceptable [13-17].
Based on the review of numerically and experimentally, the
obstacle shape can increase the turbine performance by adding
the deflector or a circular cylinder. The present study will
investigate numerically the effect of a circular cylinder
installing in front of the advancing blade varying ds/D of 0.1,
0.3 and 0.5 for each stagger angle () of 0o, 30o, and 60o. The
flow over a circular cylinder will be accelerated, however, the
maximum velocity and the minimum pressure occurs at the
upper side and lower side. The velocity through the both of bluff
body at a certain distance will cause flow interaction. Therefore,
the aim of this study will be conducted to determining the best
of a circular cylinder diameter installing on advancing blade
side with respect to Savonius turbine with respect to cylinder
diameter variations.
The present study will analyze the performance and the flow
visualization with varying ds/D of 0.1, 0.3 and 0.5 for each
stagger angle () of 0o, 30o, and 60o. The numerical will be
conducted to obtain the best performance toward he effect of a
circular cylinder includes torque coefficient (Cm), power
coefficient (Cp), the dynamic of torque coefficient, velocity
pathline structure, pressure contour, and the pressure
distribution along blade surface.
II. NUMERICAL SIMULATIONS A. Boundary Conditions and Computational Domains
The boundary conditions and the computational domain can be
seen in Fig. 1. The computational domain has three zones
namely stationary zone, wake zone, and rotating zone. It has
two interfaces. Inlet as velocity-inlet has the flow velocity (U)
of 0.22 m/s, the outlet is pressure-outlet, the lower side and the
upper side are walls, the blade of Savonius is wall and rotation.
The first interface is between the area of the rotating zone to
wake zone and the second interface is between the wake zone
and stationary zone. The upper side and lower side use
symmetry to avoid the influence of the wall. The upper side and
lower side were taken 6D from the center of the turbine. The
length from inlet to center of Savonius turbine is 6D, the length
from the center of Savonius to the outlet is 10D. This study uses
structured grids by making the first layer on the rotor surface.
The changing of circular cylinder diameter and the stagger
angle has shown in Fig. 2 for ds/D of 0.1, 0.3, and 0.5.
Fig. 1. Boundary Conditions and 2D Computational Domain.
ds/D = 0.1, 0.3 and 0.5
= 0o, 30o, and 60o
S/D = 0.95
Fig. 2. The blade position of a circular cylinder
Circular
cylinder
Coventional
Savonius
S/D
Advancing blade
Returning blade
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 153
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
(a)
(b)
(c)
(d)
Fig. 3. Mesh generation for (a) the fixed domain, (b) the wake domain, (c) the rotating domain and (d) blade
B. Mesh Generation The simulation has three (3) domains namely the fixed, the
wake, and the rotating domain. In simulation, the meshing has
used quadrilateral elements having high accuracy as presented
in Fig. 3. The surface mesh of the Savonius blade has been made
the y+ value set between 30 and 100 [16] with structure mesh
as shown in Fig. 3 (d).
The simulation uses commercial software ANSYS17.00 and
solved incompressible U-RANS for transient analysis by means
of sliding mesh for the rotation case. The simulation, increment
angle or time step rotation degree will be 1o from the results of
recommendation setting and formula by [17]. This simulation
uses the maximum iteration up to 150, it means, the turbine
rotation for 1o will be convergence for 150 iterations. On other
hands, the process will finish or the convergence has attained
with setting in about 10-5 for continuity. The verification has
conducted at TSR value of 1.078 and free stream velocity of 7
m/s from experimental data [9]. The equation of mathematics
can be written as follows:
Tip Speed Ratio (TSR)
TSR = . D
2 . U (1)
The Torque Coefficient (Cm)
Cm =T
1
4AsDU2
(2)
The Power Coefficient (Cp)
𝐶𝑝 = 𝑇𝑆𝑅 𝐶𝑚 (3)
The Number of Time Step (NTS)
NTS = N 360
(4)
The Time Step Size (TSS)
TSS = N
0.15915 ω x NTS (5)
Where the turbine rotations is denoted N (RPM), the
increment angle is denoted (o), the turbine angular speed
(rad/s) is denoted (rad/s). Equation (4) and (5) refer to [17].
From TSR, it is given =15.095 rad/s and N=144.087 RPM.
After that, N is used to calculate NTS = 51871 and than TSS =
0.0011627 that can be seen in Table 1. The verification has been
attained, the next numerical step would be compared by
experimental data from [9] at TSR of 0.5, 0.7, 0.9, 1.1 and 1.3
as shown in Table 2.
Table I
The NTS and TSS for verification [9]
TSR N
(RPM)
ω
(rad/s)
NTS
(s)
TSS
(s)
1.078 144.087 15.095 51,871 0.0011627
Table II
The NTS and TSS for using air fluid for validation [9]
TSR V
(m/s)
D
(m)
N
(RPM)
ω
(rad/s)
NTS
(s)
TSS
(s)
0.3 7 1 40.091 4.200 14,433 0.00415567 0.5 7 1 66.818 7.000 24,055 0.00249340
0.7 7 1 93.545 9.800 33,676 0.00178100
0.9 7 1 120.273 12.600 43,298 0.00138522 1.1 7 1 147.000 15.400 52,920 0.00113337
1.3 7 1 173.727 18.200 62,542 0.00095900
Table III
The NTS and TSS for using water fluid
TSR V
(m/s)
D
(m)
N
(RPM)
ω
(rad/s)
NTS
(s)
TSS
(s)
0.3 0.22 0.4 3.150 0.330 1,134 0.05289041
0.5 0.22 0.4 5.250 0.550 1,890 0.03173424 0.7 0.22 0.4 7.350 0.770 2,646 0.02266732
0.9 0.22 0.4 9.450 0.990 3,402 0.01763014
1.1 0.22 0.4 11.550 1.210 4,158 0.01442466 1.3 0.22 0.4 13.650 1.430 4,914 0.01220548
C. Verification and validation of Numerical Simulations
The firstly, the simulation has used transiently for sliding mesh.
Verification has been conducted by varying mesh from coarse
to fine 17,006, 61,105 and 120,000 nodes. The simulation has
been conducted at a tip speed ratio (TSR) of 1.078 with input
Circular
cylinder
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 154
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
data from Table 1. The verification has been conducted by
taking the data of the dynamic torque coefficient.
Fig. 4. Comparison of mesh convergence for verification
The size of the element near blade surface has been
controlled by the changing of meshing size 17,006, 61,105 and
120,000 nodes as showed in Fig .4 and have been given the
same trend results at 61,105 and 120,000 nodes. Based on Fig.4,
the mesh with 61,105 elements will be chosen for the step of
the validation because the time need considering in the
simulation.
The numerical validation has been conducted by comparing
with respect to the experimental data from [9]. The comparison
results of the average torque coefficient (Cm) between the
numerical and experimental by varying TSR of 0.5, 0.7, 0.9, 1.1
and 1.3 can be seen in Fig. 5. The graph can become a
conclusion and be considered valid for used the real problem by
installing a circular cylinder as showed in Fig. 2. The validation
of the numerical simulation has shown high accuracy in
comparison with the experimental [9] by varying TSR. The next
step will be performed by changing fluid from air to water. The
input data of the real simulation was shown in Table 2 with the
results of validation can be seen in Fig. 5.
The experimental with water fluid has been conducted by
[18] in the towing tank for low current speed show the graph of
the power coefficient (Cp) that is similar to the Savonius wind
turbine. The statement can be used for this simulation by
converting air to water. The numerical domain has been tested
to Savonius turbine for low current with the current velocity in
about 0.22 m/s. The application on Savonius turbine of vertical
axis has been conducted the validation process. The inlet as
velocity-inlet has applied for the value current velocity of 0.22
m/s. The Savonius turbine has a diameter of 0.4 m with the
sliding mesh condition for transient flow. The next numerical
simulation will be done by placing a circular cylinder on
vertical axis Savonius water turbine in front of the advancing
blade.
The secondly, the simulation will be conducted on Savonius
turbine installing of a circular cylinder with low velocity. The
numerical has been conducted at the free stream velocity about
0.22 m/s kept constant with the rotor diameter of the Savonius
turbine (D) of 0.4 m as showed in Table 3. The simulation will
be varied cylinder diameter of 0.1, 0.3, and 0.5 installed at S/D
of 0.95. The stagger angle () is 0o, 30o, and 60o kept constant.
Under the conditions, the simulation will be conducted for tip
speed ratio (TSR) from 0.5 to 1.3 by using data from Table 3.
Fig. 5. Validation of the torque coefficient (Cm) for TSR of 1.078
III. RESULTS AND DISCUSSION
A. Torque and Power Coefficient
The results of the torque coefficient at = 0o have been shown
in Fig. 6 (a) as the function of the tip speed ratio (TSR). The
trend of torque coefficient decrease by the increasing of tip
speed ratio (TSR). A circular cylinder varying ds/D has
decreased the torque coefficient of turbine. The increasing of
cylinder diameter will decrease the torque coefficient of the
turbine for all variations. The power coefficient can be called
by the performance turbine can be seen in Fig. 6 (b). The
circular cylinder diameter variations have the performance
lower than the Conventional Savonius turbine. The increasing
of the cylinder diameter has decreased turbine performance.
This matter, the increasing of the cylinder diameter will become
the blockage that has blocked the upstream flow go to the
turbine. It is very clear that placing a circular cylinder in front
of the advancing blade varying diameter (ds/D) will influence
the performance of the turbine. The further analysis is needed
the flow visualization.
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
0 30 60 90 120 150 180 210 240 270 300 330 360To
rqu
e C
oef
fici
ent
(Cm
)
(o)
17,006 nodes
61,105 nodes
120,000 nodes
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 155
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
(a)
(b)
Fig. 6 Comparison of torque coefficient (Cm) (a) and power coefficient (Cp) (b) with varying cylinder diameter (ds/D) of 0.1, 0.3 and 0.5 for = 0o
The torque coefficient (Cm) graph at = 30o has been shown
in Fig. 7 (a) as the function of the tip speed ratio (TSR). The
Cm value decrease at TSR of 0.5 but the Cm value increase in
a range of 0.9 – 1.3. A circular cylinder varying ds/D has
increased the torque coefficient of the turbine at TSR > 0.7. The
maximum torque coefficient occurs at the ds/D of 0.5. The
power coefficient can be called by the performance turbine can
be seen in Fig. 7 (b). The circular cylinder diameter variations
have the performance higher than the conventional Savonius
turbine. The increasing of the cylinder diameter has increased
turbine performance. It is very clear that placing a circular
cylinder in front of the advancing blade varying diameter (ds/D)
will influence the performance of the turbine. The further
analysis is needed the flow visualization as the velocity pathline
structure, the pressure contour, and the pressure distribution.
(a)
(b)
Fig. 7 Comparison of torque coefficient (Cm) (a) and power coefficient (Cp) (b) with varying cylinder diameter (ds/D) of 0.1, 0.3 and 0.5 for = 30o
0.00
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.32
0.36
0.40
0.44
0.5 0.7 0.9 1.1 1.3
To
rqu
e C
oef
fici
ent (C
m)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.50.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.5 0.7 0.9 1.1 1.3
Po
wer
Co
effi
cien
t (C
p)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
0.00
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.32
0.36
0.40
0.44
0.5 0.7 0.9 1.1 1.3
Torq
ue
Coef
fici
ent (C
m)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.5 0.7 0.9 1.1 1.3
Po
wer
Co
effi
cien
t (C
p)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
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The torque coefficient (Cm) graph at = 60o has been shown
in Fig. 8 (a) as the function of the tip speed ratio (TSR). The
Cm value increase by increasing the cylinder diameter. The
cylinder can cause the torque coefficient to increase. The ds/D
of 0.1 increase the Cm unsignificantly at low TSR in the range
0.5 - 1.1 having the same curve with the conventional Savonius.
The maximum torque coefficient occurs at the ds/D of 0.5. The
power coefficient can be called by the performance turbine can
be seen in Fig. 8 (b). The circular cylinder diameter variations
have the performance higher than the conventional Savonius
turbine. The increasing of the cylinder diameter has increased
turbine performance. It is very clear that placing a circular
cylinder in front of the advancing blade varying diameter (ds/D)
will influence the performance of the turbine. The results show
that the maximum turbine performance occurs at ds/D of 0.5.
Further analysis is needed the flow visualization as the velocity
pathline, the pressure contour, and the pressure distribution.
(a)
(b)
Fig. 8. Comparison of torque coefficient (Cm) and power coefficient (Cp) with varying cylinder diameter (ds/D) of 0.1, 0.3 and 0.5 for = 60o
B. The Peak Power Coefficient
The power coefficient (Cp) has been evaluated each of 0o, 30o
and 60o. The highest performance (Cp) each will be analyzed
toward the changing of a cylinder diameter (ds/D) of 0.1, 0.3,
and 0.5. The results of Cp will be interpreted as Cp gain (%)
compared between high performance at each variation with
conventional Savonius as shown in Table 4, Table 5 and Table
6. The influence of cylinder diameter (ds/D) has shown that the
cylinder diameter (ds/D) variations have low Cp results for all
variation compared to conventional Savonius. The negative
value for Cp gain (%) has shown that the performance (Cp)
decrease or the other hand, performance is lower than
conventional Savonius. Detail analysis of this phenomena will
be discussed in velocity pathline structure and pressure contour.
Table IV
The peak power coefficient at = 0o
Variation Peak Cp Corresponding
TSR
Cp Gain (%) relative to
conventional Savonius
Savonius conventional
0.213 0.9 0.00
ds/D = 0.1 0.195 0.7 -8.31
ds/D = 0.157 0.9 -26.50
ds/D = 0.142 0.7 -33.20
The analysis of peak performance at = 30o can be seen
from the peak power coefficient as shown in Table 5. The ds/D
have the peak performance lower than the conventional
indicated with the negative value. The ds/D of 0.1 have the
performance lower than the conventional. The ds/D value
increase the performance and the detail analysis of this
phenomena will be discussed in velocity pathline and pressure
contour.
Table V
The peak power coefficient at = 30o
Variation Peak Cp Corresponding
TSR
Cp Gain (%) relative to
conventional Savonius
Savonius conventional
0.213 0.9 0.00
ds/D = 0.1 0.202 0.9 -5.28
ds/D = 0.223 0.9 4.62
ds/D = 0.301 0.9 41.18
The analysis of peak performance at = 60o can be seen
from the peak power coefficient as shown in Table 6. All ds/D
have the performance higher than the conventional. Detail
analysis of this phenomena will be discussed in velocity
pathline and pressure contour.
Table VI
The peak power coefficient at = 60o
Variation Peak Cp Corresponding
TSR Cp Gain (%) relative to conventional Savonius
Savonius
conventional 0.213 0.9 0.00
ds/D = 0.1 0.216 0.9 1.53
ds/D = 0.247 0.9 15.98
ds/D = 0.288 0.7 35.29
0.00
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.32
0.36
0.40
0.44
0.5 0.7 0.9 1.1 1.3
Torq
ue
Coef
fici
ent (C
m)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.5 0.7 0.9 1.1 1.3
Po
wer
Co
effi
cien
t (C
p)
Tip Speed Ratio
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
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192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
C. Dynamic Torque coefficient with cylinder diameter (ds/D) Graph of the dynamic torque coefficient with cylinder
diameter change at the advancing blade by using the data of the
stagger angle of 60o as shown in Fig. 9. The maximum
dynamic torque coefficient occurs at a cylinder diameter of 0.5
and the lowest peak of dynamic torque coefficient occurred at a
cylinder diameter of 0.1 with the curve similar to the
conventional Savonius. The changing of ds/D will increase the
peak torque coefficient. The installation of the cylinder increase
the torque coefficient between blade angle () 0o and 90o can be
seen in Fig. 9. This shows that there is an improvement at the
advancing blade. In this case, the fluid over the advancing has
increased the positive torque that will increase the power
coefficient. The maximum torque coefficient can be predicted
at ds/D = 0.5 for = 60o and lowest torque coefficient occurred
at ds/D of 0.1. The average torque coefficient can be seen in
Table 4, 5, and 6.
Fig. 9. The dynamic torque coefficient for one rotation of Savonius turbine with cylinder diameter change for = 60o, = 30o and TSR = 0.9
D. Velocity Pathline with cylinder diameter (ds/D)
Investigation of velocity pathline has been conducted for
generating of the best analysis by investigating the velocity
pathline at ds/D of 0.5 with a blade angle of 30o. The analysis
includes the stagnation flow, vortex from returning and
advancing, attached flow and dragging flow.
(a) conventional Savonius
(c) ds/D = 0.1
(b) ds/D = 0.3
(d) ds/D = 0.5
Fig. 10. Comparison of the velocity pathline structure with cylinder diameter change for = 60o, = 30o and TSR = 0.9
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 30 60 90 120 150 180 210 240 270 300 330 360
Dyn
amic
To
rqu
e C
oef
fici
ent (
Cm
)
(deg)
Conventional Savonius
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
Stagnation flow
returning
blade
Stagnation
flow returning
blade
Vortex from
returning blade
Vortex from
advancing blade
Stagnation
flow
returning Vortex from
returning blade
Attached flow
Dragging flow
cylinder cylinder
Attached flow Attached flow
Vortex from
returning blade
Vortex from
returning blade
Stagnation flow
returning
cylinder
Vortex from
advancing blade Attached flow
Dragging flow
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 158
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
Velocity pathline will be conducted the investigation at the
advancing blade by varying ds/D of 0.1, 0.3, and 0.5 for of
60o, S/D of 0.95 kept constant, TSR of 0.9 with blade angle ()
of 30o as shown in Fig. 10. Investigation for ds/D = 0.1 shows
that the performance is the same results as the conventional. All
variations, There is no overlap flow. The stagnation flow,
vortex from returning and advancing, attached flow and
dragging flow have formed as the conventional. The stagnation
flow occurs at the same position in front of the returning blade
for all variations.
The cylinder diameter ds/D of 0.3 will cause no vortex at
the advancing blade. The attached flow has been accelerated to
obtain a high velocity. In this case, the big diameter will
decrease gap both of bluff bodies that will increase velocity at
the back surface of the advancing blade indicated the red color.
This analysis related to the pressure distribution on the next
discussion. The vortex from the advancing blade has
disappeared for ds/D of 0.3.
The ds/D of 0.5 also will cause no vortex at the advancing
blade. The attached flow has been accelerated to obtain a high
velocity. In this case, the big diameter will decrease gap both of
bluff bodies that will increase velocity at the back surface of the
advancing blade indicated the red color. The vortex from
advancing blade also has disappeared for ds/D of 0.3.
This matter has shown that the performance for S/D = 0.3
and 0.5 is more effective to improve the performance of
Savonius turbine. The analysis of vortex will refer to [8] to find
the effect of a circular cylinder toward the blade of Savonius
turbine. The overlap flow doesn’t occur at the conventional
Savonius because there is no overlap ratio in this study.
Attached flow and dragging flow has occurred at the convex
advancing blade as showed in Fig. 10. This case occurs vortex
from returning blade and advancing blade. But, a circular
cylinder has been installed in front of advancing blade and the
vortex from the advancing blade has disappeared. The
phenomena of attached flow and dragging will increase by
increasing cylinder diameter. The velocity in the attached flow
will increase by increasing the cylinder diameter.
E. Pressure contour with the cylinder diameter (ds/D)
Investigation of pressure contour with varying stagger angle
change can be seen in Fig. 11. The pressure in front of the
advancing blade is lowest in all variations. A circular cylinder
has a great contribution to decreasing pressure in the attached
flow area. The attached flow has occurred the low pressure able
to increase the positive torque and increase the power
coefficient. The flow phenomena have been investigated in
blade surface by varying ds/D=0.1, 0.3, and 0.5 for S/D=0.95,
TSR=0.9, =30o has been shown in Fig. 12. The prediction of
the highest performance uses the average Torque coefficient
(Cm) showed in Table 4, 5 and 6.
(a) conventional Savonius
(c) ds/D = 0.1
(b) ds/D = 0.3
(d) ds/D = 0.5
Fig. 11. Comparison of the pressure contour with cylinder diameter change for = 60o, = 30o and TSR = 0.9
Attached
flow
Attached
flow
Attached
flow
Attached flow
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:01 159
192501-3434-IJMME-IJENS © February 2019 IJENS I J E N S
F. Pressure distribution with cylinder diameter (ds/D)
The Pressure distribution with cylinder diameter change in
blade surface for =60o, =30o, and TSR=0.9 as shown in Fig.
12. The graph of pressure distribution has shown the higher
different pressure between front and back side at the ds/D=0.5.
It has shown a higher performance than the other stagger angle.
Observation will be conducted at the advancing side. The
advancing blade side in the concave area occurs the higher
positive pressure compared to the other. In addition, the
pressure at the convex side occurs very negatively compared to
the other. The ds/D=0.5 have the highest net pressure drag and
the torque at the advancing blade side is the highest for this case
study. As a decision, the analysis always uses the average
torque coefficient that can be seen in Table 4, 5 and 6.
Fig. 12. Pressure distribution in blade surface with cylinder diameter change
for = 60o, = 30o and TSR = 0.9
IV. CONCLUSION
Based on the results of numerical and discussion above for
the changing of ds/D of 0.1, 0.3, and 0.5, concluded as follow:
1. The ds/D=0.5 has the highest torque coefficient at =30o
and =60o. The torque coefficient has decreased at =0o, a
circular cylinder block the flow go to downstream.
2. The ds/D=0.5 has the highest performance at =30o and
=60o. The performance has decreased at =0o because a
circular cylinder will become a blockage.
3. The dynamic torque coefficient shows the improvement of
the performance at the advancing blade side.
4. There is no overlap flow in the conventional Savonius. All
variations use without overlap ratio.
5. The velocity increase by increasing the ds/D at the
attached flow zone.
6. Pressure contour shows the net pressure between in front
and the back side is highest at ds/D=0.5.
7. Pressure distribution shows the increase of pressure
different on the advancing zone caused by installing a
circular cylinder at stagger angle of 30 or 60 degree.
ACKNOWLEDGMENT
The authors would like to thank the Shipbuilding Institute of
Polytechnic Surabaya has given for all support to finished this
researches.
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01020304050
-0.20 -0.16 -0.12 -0.08 -0.04 0.00 0.04 0.08 0.12 0.16 0.20
Pre
ssure
(P
a)
X (m)
Conventional
ds/D = 0.1
ds/D = 0.3
ds/D = 0.5
Advancing blade Returning blade