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,



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



(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



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



(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


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


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


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


ds/D = 0.1

ds/D = 0.3

ds/D = 0.5



The torque coefficient (Cm) graph at = 60o has been shown


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



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



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


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


ds/D = 0.1

ds/D = 0.3

ds/D = 0.5



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)


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



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



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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Pre

ssure

(P

a)

X (m)

Conventional

ds/D = 0.1

ds/D = 0.3

ds/D = 0.5

Advancing blade Returning blade

effect of a circular cylinder in front of advancing blade on the...

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