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 1Mechanical Engineering Department,Engineering Faculty, Udayana University, Bali ,Indonesiaaemail: [email protected], bemail: [email protected], cemail:[email protected]
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 :
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 O-ring 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]
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] :
)
Drag coefficient based on frontal area effectively cylinder calculated using the equation [5]:
) manometer, cylinder with rectangular ring, and blower. The arrangement of the equipment test as showed in Fig.2.
Fig.2. Installation Schematic
Where :
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.
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
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
L
D
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.
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, FluidDynamics 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
