The influence of distance variation between rings with sloping position on the cylinder surface to drag coefficient.
Applied Mechanics and Materials Vol 776 (2015) pp 384-389
© (2015) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.776.384
Submitted: 2015-02-19
Accepted: 2015-04-10
The Influence of Distance Variation Between Rings with Sloping
Position on The Cylinder Surface to Drag Coefficient
Si Putu Gede Gunawan Tista 1,a, Ainul Ghurri 1,b, Hendra Wijaksana 1,c
1
Mechanical Engineering Department,Engineering Faculty, Udayana University, Bali ,Indonesia
a
email: Gunawan_tista@yahoo.com, bemail: a.ghurri@gmail.com, cemail:wehawe@gmail.com
Keywords : Distance between rings, Quadrangular ring, Sloping ring position, Cylinder, Drag
coefficient.
Abstract. There are so many equipment using cylinder in its application, such as bridge support
column, smoke chimney, pole pillar of offshore oil drilling etc. When those kind of equipment is
affected by air flow continuously, it would reducing the strength of those equipment construction.
This strength reduction is caused by the drag force that is emerged due to the air flow and its
direction are having the same direction with flow direction. So that it is necessary to do something
to reduce the drag, one of it is by adding the rectangular ring at the cylinder surface. The rings is
placed at the cylinder surface in 100 sloping position and then its ring distance would be varied. The
aim of this research is to discover the influences of distance variation between the ring with sloping
position on the cylinder surface to the drag coefficient. This research is conducted in the wind
tunnel that consist of blower, pitot pipe, U manometer, inclined manometer, digital weight,
cylinder, quadrangular rings (attached on the cylinder). The cylinder is placed in vertical position
within the distance between the rings is varied as L/D = 0.5, 0.67, 0.83, 1.00, and 1.17. The Reynold
number based on silinder diameter D = 60 mm is Re = 3.64 X 104 . Pressure distribution is
determined by measuring cylinder surface pressure at 36 points with 100 interval. The result of this
research showed that the lowest drag coefficient value occurs at the distance between the ring of
L/D = 0.5 is 0.485. The large decreasing of the drag coefficient compare to without rings is 43.5%.
Introduction
Phenomena of fluid flow movement through a bluff body is very importance in engineering
applications such as calorie exchanger, combustion, transportation, smoke chimney, and buildings.
Accordingly this flow phenomena research become important relates to the present world energy
crisis. The flow pattern would be different depend on the body bluff geometric such as cylinder,
rectangular and plat . Viscous external stream that flowing through the cylinder would be
experienced stagnant, boundary layer, separation and wake on the back of cylinder. For the moving
object in fluid viscous, the drag force and lift force have a strong relation with stream separation
[1].
The stream separation would the rise of the wake on the back of cylinder which cause the drag.
The faster the occurring of the stream separation, the wake will be wider and so that the drag
become larger.
In engineering application, there is so many equipment that uses cylinder such as bridge
support column, smoke chimney, pole pillar of the offshore oil drilling. When those kind of
equipment is affected by air flow continuously, it would reducing the strength of those equipment
construction. This having the same direction with flow direction. So that it is necessary to do
research in reducing the drag force. In this research , on the cylinder would be placed the
rectangular ring in 100 sloping position, so that there will be change the stream pattern on cylinder,
it expected the stream separation can be delayed, it then the wake on the back of cylinder would be
narrowed and drag on the cylinder would be reduce. The objective of this research is to be
knowledgeable about the influences of the distance between variation of rectangular ring in sloping
position on the cylinder surface to the drag coefficient.
Several research about the drag that support this research including :
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications, www.ttp.net. (ID: 114.79.45.167-18/05/15,05:23:10)
Applied Mechanics and Materials Vol. 776
385
Lee, at.all.(2004), it examined the influence of placing a small control stick at the upstream of the
cylinder which is focused on the drag characteristic and stream structure. The Reynold number
based on prime cylinder ( D=30 mm) is founded of Re = 2000. The diameter of the stick control is
then to be varied from 4 to 8, while the length of peak distance, L is varied in 45, 50, 55, 60, 62.5,
65, 70, 90, 105, and 120 mm. The drag coefficient reduction from the whole system including
prime cylinder and stick control. The maximum of the drag coefficient reduction from the prime
cylinder without stick control is 29%. Then the maximum of total drag coefficient reduction from
the whole system which is including prime cylinder and stick control is 25% for peak distance ratio,
L/D = 1.833 within diameter of the stick control d/D = 0.233.
Tsutsui & Igarashi (2002), it evaluated the stream around cylinder by placing a small stick on the
upstream cylinder. Cylinder diameter, D = 40 mm and stick diameter ranging, d from 1 to 10 mm.
The distance between the axis of cylinder and stick , L = 50 – 120 mm. Reynold number based on
Diameter, ranging from 1.5 X 104 to 6.2 X 104. It occurred two patterns of stream with and without
vortex shedding from the stick. The stream pattern changes depend on stick diameter, position, and
Reynold number. The optimum condition of the drag reduction is on d/D = 0.25 , L/D = 1.75 – 2.0.
In this condition, the vortex would not fall from the stick and the shearing boundary of the stick
would occupied front face of the cylinder.
Lim & Lee ( 2004 ) , discuss about stream around circle cylinder that is controlled by sticking Oring to reduce drag force on the cylinder. The drag force, wake velocity and turbulent intensity is
measured on Reynold number in the range of ReD = 7.8 X 103 - 1.2 X 105 within the variation of
combination diameter and peak distance among adjacent O-ring. It found that cylinder with
diameter O-ring , d = 0.0167 D on the peak interval of distance of peak to peak (PPD) = 0.165 D,
showing that the maximum drag reduction is around 9% on ReD = 1.2 X 105, compared to smooth
cylinder. But the placement of O-ring for larger diameter than d = 0.067 D would only result a small
drag reduction.
Yajima & Sono (1996 ), it evaluates the stream around cylinder by making holes along cylinder in
two rows, which is set across the cylinder.The extreme drag reduction can be achieved for many
attack angle, in which the drag reduction founded is 40% larger than smooth cylinder.
Basic Theory
Incompressible stream crossed the cylinder can be seen in Fig.1.
(a) Viscous flow
(b) Inviscid flow
Fig.1. Qualitative Picture of incompressible flow over a cylinder [2]
On the Fig.1.a. It showed viscous stream on the cylinder, streamlines is symmetrical. Point A is
the stagnation point and boundary layer occurred. From Point A to Point B, it occurs velocity
increase, that caused pressure reduction and Point B to Point C would occur velocity decrease,
which is mean there will be the increasing of pressure, PC > PB. At Point C, the momentum of
stream is not able to against shear stress so that it would caused the break of the boundary layer.
Point C is called as Point of Separation. Between those points and separation place of boundary
layer, it appears an area which is called Wake. The larger the wake, the larger different force occurs
on the front and the back of cylinder, that again would cause the larger the drag force of the stream
on the cylinder. Inviscid stream is figured on Fig.1.b. It can be seen that it symmetrical streamlines,
it occurred slip on the surface of cylinder and the different size of the stream velocity is showed by
386
Recent Decisions in Technologies for Sustainable Development
the density of the streamlines and there is no wake occurred, so that it would not occurred the drag
force on the cylinder.
In this research, the determination of pressure coefficient is used equation [4] :
CP =
P − Po
1
ρU o 2
2
(1)
Where :
P
= Surface pressure (N/m2)
Po = Static Pressure (N/m2)
Uo = Free stream velocity (m/s)
ρ
= Air density (kg/m3)
Drag coefficient based on frontal area effectively cylinder calculated using the equation [5]:
F
C D = 1 D2
( 2)
ρU 0 . A
2
Where :
FD = Drag force (N)
A = The Frontal area of a cylinder (m2)
Uo = Free stream velocity (m/s)
ρ = Air density (kg/m3)
Research Method
The equipment which is used in this research are including : wind tunnel, pitot pipe,
manometer, cylinder with rectangular ring, and blower. The arrangement of the equipment test as
showed in Fig.2.
Fig.2. Installation Schematic
Where :
1.
2.
3.
4.
Blower
Wind Tunnel
Pitot pipe
U Manometer
5. Inclined Manometer
6.
7.
8.
9.
Rail/Track
Digital Weight
Handle
Test Speciment
10. Director
In the following figure ( Fig.3), It showed the detail of cylinder with sloping ring and the
distance variety between the rings i.e. 30, 40, 50, 60, and 70 mm.
Applied Mechanics and Materials Vol. 776
387
L
D
Fig.3. Cylinder Details with Sloping Ring, and Distance between rings 30, 40, 50, 60, and 70 mm
For the distance variation, it used L/D which is the comparison between the distance of sloping
ring and cylinder diameter
60mm
Fig.4. Configuration of 36 Testing Holes , Cp
Data Collecting Procedure
The data collecting procedure is conducted after determining or measuring the whole
instrument that support in this data collecting procedure.
Data Collecting Steps :
1. Placing the cylinder with its vertical rectangular ring in the wind tunnel in the front of
subsonic tunnel.
2. Starts the blower.
3. When the blower has already stable, conduct data collection.
4. The data collection of the pressure distribution with the variation of the distance between
ring with 10o sloping angle, is conducted by collecting the data from the cylinder surface.
5. The data collection is taken three times at every variation of distance between ring. The
testing is conducted for cylinder with or without rectangular rings, and also for the free
stream velocity in the front of subsonic tunnel and for the static force as well.
6. The data collection for the mass within the variation of the distance between rings, with or
without rectangular ring is taken three times.
Results and Discuss
The research results on the cylinder with rectangular ring, 10o sloping angle ring, air stream
velocity Uo = 8.8 m/s, Reynold number Re = 3.64 X 104 can be seen in Fig.5 and Fig.6
388
Recent Decisions in Technologies for Sustainable Development
0.2
0.15
0.1
without ring
sloping ring L/D=0,5
0.05
Cp
sloping ring L/D=0,67
0
-0.05
0
40
80 120 160 200 240 280 320 360
sloping ring L/D=0,83
sloping ring L/D=1
-0.1
sloping ring L/D=1,17
-0.15
-0.2
Angle ( θ)
Fig.5. The Relationship between The Pressure Coefficient (CP) and The Cylinder Angle (θ ) with
the variation of the distance between sloping ring and without ring.
On the Fig.5, It can be shown the relationship between the pressure coefficient and the cylinder
angle with the variation of distance between the sloping ring of L/D = 0.5 ; 0.67 ; 0.83 ; 1.0 ; and
1.17, also without ring. It can be seen that the pressure of stagnation point would decrease and then
increase, and at the end there will be stream separation. The stream separation occurred in the angle
of 90o without ring until 110o with the variation of the distance between ring. It clear that the
existing of the ring on the cylinder which is placed with 10o sloping angle would cause the delay of
stream separation until the angle of 110o which is occur on the smallest ring distance of L/D = 0.5.
It then caused the wake (area at the back of cylinder) become narrower so that the drag will be
lower. This phenomena occurs as at the smallest distance of the ring, the stream on the cylinder
surface become faster, then the stream momentum become larger to overcome the shear stress. The
increase of air stream velocity is caused by the stream separation on the ring spread out to the
cylinder surface between the ring, so that the stream which flowing through the narrow area would
increase.
1
0.9
0.857
0.8
0.7
0.6
0.568
CD 0.5
0.610
0.650
without ring
0.485 0.486
0.4
sloping ring
0.3
0.2
0.1
0
0
0.5
L/D
1
1.5
Fig.6. The Relationship between the drag coefficient (CD) and the distance between the sloping ring
(L/D) and without ring
On the Fig.6, It can be shown the relationship between the drag coefficient (CD) and the
distance between the sloping ring (L/D) and without ring. It shown the decrease of the drag
Applied Mechanics and Materials Vol. 776
389
coefficient occurs by adding ring compared to without ring. On the cylinder with sloping ring, the
drag coefficient increase from the distance of L/D = 0.5 until L/D = 1.17, due to at the smallest
distance ring of L/D = 0.5, the stream velocity become larger, so that the stream momentum become
larger to overcome the shear stress, then the stream separation would be delayed and the wake
become narrower, the drag become lower. The largest decreasing of the drag coefficient occurs at
the distance between sloping ring of L/D = 0.5, and its drag coefficient value, is CD = 0.485 While
the drag coefficient value for without ring is CD = 0.857.The decreasing of the maximum drag
compared to without ring is 43.4%.
Conclusions
From this research, it can be concluded that :
1. By placing the sloping ring on the cylinder, it would result the decreasing of the drag
coefficient compared to the cylinder without ring.
2. the bigger the distance between sloping ring , the bigger the drag coefficient
3. The largest drag coefficient is occurred at the distance between sloping ring of L/D = 0.5
References
[1] Chew, Y T., L S Pan, dan T S Lee, Numerical Simulation Of The Effect Of a Moving Wall On
Separation Of Flow Past a Symmetrical Aerofoil, ImechE, 212.
[2] Fox, R. W.,Introduction To Fluid Mechanics. John Wiley & Sons, New York,1985.
[3] Igarashi, T., Drag Reduction Of a Square Prism by Flow Control Using a Small Rod, Journal of
Wind Engineering and Industrial Aerodynamics, 69 – 71(1997), 141 – 153.
[4] Lee, S., S. Lee, dan C. Park, Reducing The Drag On a Circular Cylinder by Upstream
Installation Of a Small Control Rod, Fluid Dynamics Reseach , 34(2004): 233-250.
[5] Lim, H.C.dan.Lee S.J., Flow Control of Circular Cylinder With O-Rings , Fluid Dynamics
Research, 35 (2004): 107 – 122
[6] Tsutsui, T. dan T. Igarashi, Drag Reduction of a Circular Cylinder in an Air-Stream, Journal of
Wind Engineering and Industrial Aerodynamics, 90(2002): 527-541.
[7] Yajima, Y dan O. Sano, A Note On The Drag Reduction Of a Circular Cylinder Due To Double
Rows Of Holes, Fluid Dynamics Research, 18(1996): 237 – 243.
© (2015) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.776.384
Submitted: 2015-02-19
Accepted: 2015-04-10
The Influence of Distance Variation Between Rings with Sloping
Position on The Cylinder Surface to Drag Coefficient
Si Putu Gede Gunawan Tista 1,a, Ainul Ghurri 1,b, Hendra Wijaksana 1,c
1
Mechanical Engineering Department,Engineering Faculty, Udayana University, Bali ,Indonesia
a
email: Gunawan_tista@yahoo.com, bemail: a.ghurri@gmail.com, cemail:wehawe@gmail.com
Keywords : Distance between rings, Quadrangular ring, Sloping ring position, Cylinder, Drag
coefficient.
Abstract. There are so many equipment using cylinder in its application, such as bridge support
column, smoke chimney, pole pillar of offshore oil drilling etc. When those kind of equipment is
affected by air flow continuously, it would reducing the strength of those equipment construction.
This strength reduction is caused by the drag force that is emerged due to the air flow and its
direction are having the same direction with flow direction. So that it is necessary to do something
to reduce the drag, one of it is by adding the rectangular ring at the cylinder surface. The rings is
placed at the cylinder surface in 100 sloping position and then its ring distance would be varied. The
aim of this research is to discover the influences of distance variation between the ring with sloping
position on the cylinder surface to the drag coefficient. This research is conducted in the wind
tunnel that consist of blower, pitot pipe, U manometer, inclined manometer, digital weight,
cylinder, quadrangular rings (attached on the cylinder). The cylinder is placed in vertical position
within the distance between the rings is varied as L/D = 0.5, 0.67, 0.83, 1.00, and 1.17. The Reynold
number based on silinder diameter D = 60 mm is Re = 3.64 X 104 . Pressure distribution is
determined by measuring cylinder surface pressure at 36 points with 100 interval. The result of this
research showed that the lowest drag coefficient value occurs at the distance between the ring of
L/D = 0.5 is 0.485. The large decreasing of the drag coefficient compare to without rings is 43.5%.
Introduction
Phenomena of fluid flow movement through a bluff body is very importance in engineering
applications such as calorie exchanger, combustion, transportation, smoke chimney, and buildings.
Accordingly this flow phenomena research become important relates to the present world energy
crisis. The flow pattern would be different depend on the body bluff geometric such as cylinder,
rectangular and plat . Viscous external stream that flowing through the cylinder would be
experienced stagnant, boundary layer, separation and wake on the back of cylinder. For the moving
object in fluid viscous, the drag force and lift force have a strong relation with stream separation
[1].
The stream separation would the rise of the wake on the back of cylinder which cause the drag.
The faster the occurring of the stream separation, the wake will be wider and so that the drag
become larger.
In engineering application, there is so many equipment that uses cylinder such as bridge
support column, smoke chimney, pole pillar of the offshore oil drilling. When those kind of
equipment is affected by air flow continuously, it would reducing the strength of those equipment
construction. This having the same direction with flow direction. So that it is necessary to do
research in reducing the drag force. In this research , on the cylinder would be placed the
rectangular ring in 100 sloping position, so that there will be change the stream pattern on cylinder,
it expected the stream separation can be delayed, it then the wake on the back of cylinder would be
narrowed and drag on the cylinder would be reduce. The objective of this research is to be
knowledgeable about the influences of the distance between variation of rectangular ring in sloping
position on the cylinder surface to the drag coefficient.
Several research about the drag that support this research including :
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications, www.ttp.net. (ID: 114.79.45.167-18/05/15,05:23:10)
Applied Mechanics and Materials Vol. 776
385
Lee, at.all.(2004), it examined the influence of placing a small control stick at the upstream of the
cylinder which is focused on the drag characteristic and stream structure. The Reynold number
based on prime cylinder ( D=30 mm) is founded of Re = 2000. The diameter of the stick control is
then to be varied from 4 to 8, while the length of peak distance, L is varied in 45, 50, 55, 60, 62.5,
65, 70, 90, 105, and 120 mm. The drag coefficient reduction from the whole system including
prime cylinder and stick control. The maximum of the drag coefficient reduction from the prime
cylinder without stick control is 29%. Then the maximum of total drag coefficient reduction from
the whole system which is including prime cylinder and stick control is 25% for peak distance ratio,
L/D = 1.833 within diameter of the stick control d/D = 0.233.
Tsutsui & Igarashi (2002), it evaluated the stream around cylinder by placing a small stick on the
upstream cylinder. Cylinder diameter, D = 40 mm and stick diameter ranging, d from 1 to 10 mm.
The distance between the axis of cylinder and stick , L = 50 – 120 mm. Reynold number based on
Diameter, ranging from 1.5 X 104 to 6.2 X 104. It occurred two patterns of stream with and without
vortex shedding from the stick. The stream pattern changes depend on stick diameter, position, and
Reynold number. The optimum condition of the drag reduction is on d/D = 0.25 , L/D = 1.75 – 2.0.
In this condition, the vortex would not fall from the stick and the shearing boundary of the stick
would occupied front face of the cylinder.
Lim & Lee ( 2004 ) , discuss about stream around circle cylinder that is controlled by sticking Oring to reduce drag force on the cylinder. The drag force, wake velocity and turbulent intensity is
measured on Reynold number in the range of ReD = 7.8 X 103 - 1.2 X 105 within the variation of
combination diameter and peak distance among adjacent O-ring. It found that cylinder with
diameter O-ring , d = 0.0167 D on the peak interval of distance of peak to peak (PPD) = 0.165 D,
showing that the maximum drag reduction is around 9% on ReD = 1.2 X 105, compared to smooth
cylinder. But the placement of O-ring for larger diameter than d = 0.067 D would only result a small
drag reduction.
Yajima & Sono (1996 ), it evaluates the stream around cylinder by making holes along cylinder in
two rows, which is set across the cylinder.The extreme drag reduction can be achieved for many
attack angle, in which the drag reduction founded is 40% larger than smooth cylinder.
Basic Theory
Incompressible stream crossed the cylinder can be seen in Fig.1.
(a) Viscous flow
(b) Inviscid flow
Fig.1. Qualitative Picture of incompressible flow over a cylinder [2]
On the Fig.1.a. It showed viscous stream on the cylinder, streamlines is symmetrical. Point A is
the stagnation point and boundary layer occurred. From Point A to Point B, it occurs velocity
increase, that caused pressure reduction and Point B to Point C would occur velocity decrease,
which is mean there will be the increasing of pressure, PC > PB. At Point C, the momentum of
stream is not able to against shear stress so that it would caused the break of the boundary layer.
Point C is called as Point of Separation. Between those points and separation place of boundary
layer, it appears an area which is called Wake. The larger the wake, the larger different force occurs
on the front and the back of cylinder, that again would cause the larger the drag force of the stream
on the cylinder. Inviscid stream is figured on Fig.1.b. It can be seen that it symmetrical streamlines,
it occurred slip on the surface of cylinder and the different size of the stream velocity is showed by
386
Recent Decisions in Technologies for Sustainable Development
the density of the streamlines and there is no wake occurred, so that it would not occurred the drag
force on the cylinder.
In this research, the determination of pressure coefficient is used equation [4] :
CP =
P − Po
1
ρU o 2
2
(1)
Where :
P
= Surface pressure (N/m2)
Po = Static Pressure (N/m2)
Uo = Free stream velocity (m/s)
ρ
= Air density (kg/m3)
Drag coefficient based on frontal area effectively cylinder calculated using the equation [5]:
F
C D = 1 D2
( 2)
ρU 0 . A
2
Where :
FD = Drag force (N)
A = The Frontal area of a cylinder (m2)
Uo = Free stream velocity (m/s)
ρ = Air density (kg/m3)
Research Method
The equipment which is used in this research are including : wind tunnel, pitot pipe,
manometer, cylinder with rectangular ring, and blower. The arrangement of the equipment test as
showed in Fig.2.
Fig.2. Installation Schematic
Where :
1.
2.
3.
4.
Blower
Wind Tunnel
Pitot pipe
U Manometer
5. Inclined Manometer
6.
7.
8.
9.
Rail/Track
Digital Weight
Handle
Test Speciment
10. Director
In the following figure ( Fig.3), It showed the detail of cylinder with sloping ring and the
distance variety between the rings i.e. 30, 40, 50, 60, and 70 mm.
Applied Mechanics and Materials Vol. 776
387
L
D
Fig.3. Cylinder Details with Sloping Ring, and Distance between rings 30, 40, 50, 60, and 70 mm
For the distance variation, it used L/D which is the comparison between the distance of sloping
ring and cylinder diameter
60mm
Fig.4. Configuration of 36 Testing Holes , Cp
Data Collecting Procedure
The data collecting procedure is conducted after determining or measuring the whole
instrument that support in this data collecting procedure.
Data Collecting Steps :
1. Placing the cylinder with its vertical rectangular ring in the wind tunnel in the front of
subsonic tunnel.
2. Starts the blower.
3. When the blower has already stable, conduct data collection.
4. The data collection of the pressure distribution with the variation of the distance between
ring with 10o sloping angle, is conducted by collecting the data from the cylinder surface.
5. The data collection is taken three times at every variation of distance between ring. The
testing is conducted for cylinder with or without rectangular rings, and also for the free
stream velocity in the front of subsonic tunnel and for the static force as well.
6. The data collection for the mass within the variation of the distance between rings, with or
without rectangular ring is taken three times.
Results and Discuss
The research results on the cylinder with rectangular ring, 10o sloping angle ring, air stream
velocity Uo = 8.8 m/s, Reynold number Re = 3.64 X 104 can be seen in Fig.5 and Fig.6
388
Recent Decisions in Technologies for Sustainable Development
0.2
0.15
0.1
without ring
sloping ring L/D=0,5
0.05
Cp
sloping ring L/D=0,67
0
-0.05
0
40
80 120 160 200 240 280 320 360
sloping ring L/D=0,83
sloping ring L/D=1
-0.1
sloping ring L/D=1,17
-0.15
-0.2
Angle ( θ)
Fig.5. The Relationship between The Pressure Coefficient (CP) and The Cylinder Angle (θ ) with
the variation of the distance between sloping ring and without ring.
On the Fig.5, It can be shown the relationship between the pressure coefficient and the cylinder
angle with the variation of distance between the sloping ring of L/D = 0.5 ; 0.67 ; 0.83 ; 1.0 ; and
1.17, also without ring. It can be seen that the pressure of stagnation point would decrease and then
increase, and at the end there will be stream separation. The stream separation occurred in the angle
of 90o without ring until 110o with the variation of the distance between ring. It clear that the
existing of the ring on the cylinder which is placed with 10o sloping angle would cause the delay of
stream separation until the angle of 110o which is occur on the smallest ring distance of L/D = 0.5.
It then caused the wake (area at the back of cylinder) become narrower so that the drag will be
lower. This phenomena occurs as at the smallest distance of the ring, the stream on the cylinder
surface become faster, then the stream momentum become larger to overcome the shear stress. The
increase of air stream velocity is caused by the stream separation on the ring spread out to the
cylinder surface between the ring, so that the stream which flowing through the narrow area would
increase.
1
0.9
0.857
0.8
0.7
0.6
0.568
CD 0.5
0.610
0.650
without ring
0.485 0.486
0.4
sloping ring
0.3
0.2
0.1
0
0
0.5
L/D
1
1.5
Fig.6. The Relationship between the drag coefficient (CD) and the distance between the sloping ring
(L/D) and without ring
On the Fig.6, It can be shown the relationship between the drag coefficient (CD) and the
distance between the sloping ring (L/D) and without ring. It shown the decrease of the drag
Applied Mechanics and Materials Vol. 776
389
coefficient occurs by adding ring compared to without ring. On the cylinder with sloping ring, the
drag coefficient increase from the distance of L/D = 0.5 until L/D = 1.17, due to at the smallest
distance ring of L/D = 0.5, the stream velocity become larger, so that the stream momentum become
larger to overcome the shear stress, then the stream separation would be delayed and the wake
become narrower, the drag become lower. The largest decreasing of the drag coefficient occurs at
the distance between sloping ring of L/D = 0.5, and its drag coefficient value, is CD = 0.485 While
the drag coefficient value for without ring is CD = 0.857.The decreasing of the maximum drag
compared to without ring is 43.4%.
Conclusions
From this research, it can be concluded that :
1. By placing the sloping ring on the cylinder, it would result the decreasing of the drag
coefficient compared to the cylinder without ring.
2. the bigger the distance between sloping ring , the bigger the drag coefficient
3. The largest drag coefficient is occurred at the distance between sloping ring of L/D = 0.5
References
[1] Chew, Y T., L S Pan, dan T S Lee, Numerical Simulation Of The Effect Of a Moving Wall On
Separation Of Flow Past a Symmetrical Aerofoil, ImechE, 212.
[2] Fox, R. W.,Introduction To Fluid Mechanics. John Wiley & Sons, New York,1985.
[3] Igarashi, T., Drag Reduction Of a Square Prism by Flow Control Using a Small Rod, Journal of
Wind Engineering and Industrial Aerodynamics, 69 – 71(1997), 141 – 153.
[4] Lee, S., S. Lee, dan C. Park, Reducing The Drag On a Circular Cylinder by Upstream
Installation Of a Small Control Rod, Fluid Dynamics Reseach , 34(2004): 233-250.
[5] Lim, H.C.dan.Lee S.J., Flow Control of Circular Cylinder With O-Rings , Fluid Dynamics
Research, 35 (2004): 107 – 122
[6] Tsutsui, T. dan T. Igarashi, Drag Reduction of a Circular Cylinder in an Air-Stream, Journal of
Wind Engineering and Industrial Aerodynamics, 90(2002): 527-541.
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