THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
1.0Title
MEC 554-THERMALFLUIDS LAB THERMODYNAMICS II LAB
DRAG IN FORCE LAYER OVER A BODY
LECTURER: Siti Noor Azizzati Mohd Noor
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
2.0Abstract
In this experiment the most important parameter is Reynolds number, where for the present, we considered how external flow and its associated lift and drag vary as a function of Reynolds number. Sharp edges always cause flow separation and high drag that is insensitive to the Reynolds number. This experiment can be summarising by comparing the drag force between both orientations. The body base facing upstream have the higher value of drag force than facing downstream even though they are having same geometry shape.
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
List of Symbols A
Area over which force (F) acts (m2)
E
Elastic modulus (GPa)
F
Force (N)
( )
Initial dimension in direction i (mm)
T
Specimen thickness (m) Rate of chart displacement (mm/min) Rate of sample displacement (mm/min)
w
Specimen width (m) Displacement of chart (mm) Displacement of sample (mm) Strain =0
Predicted strain at zero stress Normal strain in direction i
E
Error in the predicted elastic modulus (GPa)
F
Error in the force (N) Change in dimension in direction i (mm)
t
Error in the specimen thickness (m)
w
Error in the width (m) =0
Error in the predicted strain at zero stress Error in the predicted intercept of stress-stain data (MPa) Error in the stress (MPa) Predicted intercept of stress-strain data (MPa) Engineering stress (MPa) Yield point (MPa) Ultimate strength (MPa)
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
Table of Contents 1.0
Title............................................................................................................................................. 1
2.0
Abstract...................................................................................................................................... 2
List of Symbols ........................................................................................................................................ 3 List of figure ......................................................................................................................................... 5 List of table ........................................................................................................................................... 5 3.0
Introduction And Applications .................................................................................................. 6
4.0
Objectives.................................................................................................................................... 7
5.0
Theory ......................................................................................................................................... 7
6.0 Experimental Procedures .............................................................................................................. 9 6.1 Apparatus and experiment set up ................................................................................................ 9 6.2 Procedure .................................................................................................................................... 10 7.0
Results....................................................................................................................................... 11
7.1 Data recorded ............................................................................................................................. 11 7.2 Data Analysis ............................................................................................................................... 12 7.3 Sample Calculation ...................................................................................................................... 13 8.0
Discussion ................................................................................................................................. 14
9.0
Conclusion ................................................................................................................................ 14
10.0
References and appendices ..................................................................................................... 15
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
List of figure Figure 1: Schematic diagram of drag force for Boat hulls ...................................................................... 6 Figure 2: Boat hulls ................................................................................................................................. 6 Figure 3: Rigid rod and Hemisphere with body base facing downstream and upstream ...................... 9 Figure 4: Weight balance ........................................................................................................................ 9 Figure 5: Speed control ........................................................................................................................... 9 Figure 6: Sub sonic wind tunnel .............................................................................................................. 9 Figure 7: Graph of Drag Coefficient, CD against Rey. No ...................................................................... 12
List of table Table 1: Tabulated data ........................................................................................................................ 11
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
3.0 Introduction And Applications In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) refers to forces acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity. Drag forces always decrease fluid velocity relative to the solid object in the fluid's path. Example of drag include the component of the net aerodynamic or hydrodynamic force acting opposite to the direction of movement of the solid object relative to the Earth as for cars, aircraft and boat hulls, or acting in the same geographical direction of motion as the solid, as for sails attached to a downwind sail boat, or in intermediate directions on a sail depending on points of sail. In the case of viscous drag of fluid in a pipe, drag force on the immobile pipe decreases fluid velocity relative to the pipe.
Figure 2: Boat hulls
The drag
coefficient (commonly
Figure 1: Schematic diagram of drag force for Boat hulls
denoted
as: cd, cx or cw)
is
a dimensionless
quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equation, where a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. The drag coefficient is always associated with a particular surface area. The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag: skin friction and form drag. The drag coefficient of a lifting air foil or hydrofoil also includes the effects of lift-induced drag. The drag coefficient of a complete structure such as an aircraft also includes the effects of interference drag.
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
4.0 Objectives The purpose of this experiment is to:
1. To measure the drag coefficient CD, over a range of velocities in the test section for hemispherical (open end facing flow or upstream and open end facing down the stream). 2. To understand the uses of drag force.
5.0 Theory According to http://www.grc.nasa.gov, drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field or an electromagnetic field, where one object can affect another object without being in physical contact. For drag to be generated, the solid body must be in contact with the fluid. If there is no fluid, there is no drag. Drag is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid. If there is no motion, there is no drag. It makes no difference whether the object moves through a static fluid or whether the fluid moves past a static solid object. Drag is a force and is therefore a vector quantity having both a magnitude and a direction. Drag acts in a direction that is opposite to the motion of the aircraft. Lift acts perpendicular to the motion. There are many factors that affect the magnitude of the drag. Generally, types of drag are divided into the following categories: 1.
parasitic drag, consisting of
form drag,
skin friction,
interference drag,
2.
lift-induced drag, and
3.
wave drag (aerodynamics) or wave resistance (ship hydrodynamics).
(source: http://en.wikipedia.org/wiki/Drag_(physics) Page | 7
THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
Mathematically, drag coefficient can be written as follow:
This was derived from the equation: ,
where, FD = drag force ρ = mass density of the fluid v = velocity of the object relative to the fluid A = reference area CD = drag coefficient (dimensionless)
The drag coefficient depends on the shape of the object and on the Reynolds number:
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
6.0 Experimental Procedures 6.1 Apparatus and experiment set up
Figure 6: Sub sonic wind tunnel
Figure 5: Speed control
Figure 4: Weight balance
Figure 3: Rigid rod and Hemisphere with body base facing downstream and upstream
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
6.2 Procedure 1. Diameter of hemisphere is measured. 2. First, the rigid rod is fitted to the balance arm. 3. The arm is balanced to zero. 4. The blower fan then switched ON to flow velocity 8 m/s. 5. The arm is balanced once again and the reading is recorded. 6. The velocity is increased with decrement of 2 m/s until 20 m/s. The arm is balanced for each reading. 7. Step 1 until step 6 are repeated by changing the rigid rod with hemisphere body with open end facing the flow and then open end facing down the stream.
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
7.0
Results
7.1 Data recorded Rigid Body base surface facing Rod upstream Drag Drag Net Drag Force, Force, Drag Coefficient, FD (N) FD (N) Force, CD (N) FD (N)
Body base surface facing downstream Drag Net Force, Drag FD (N) Force, FD (N)
Drag Coefficient, CD (N)
Net Drag Coefficient, CD
No
Velocity (m/s)
Rey. No. (x103)
1
0
0
0
0
0
0
0
0
0
0
2
8
34.305
0.02
0.21
0.19
1.1672
0.08
0.06
0.3686
0.7986
3
10
42.882
0.02
0.31
0.29
1.1402
0.10
0.08
0.3145
0.8257
4
12
51.459
0.02
0.48
0.46
1.2559
0.15
0.13
0.3549
0.9010
5
14
60.035
0.06
0.66
0.60
1.2036
0.21
0.15
0.3009
0.9027
6
16
68.612
0.06
0.86
0.80
1.2287
0.28
0.22
0.3379
0.8908
7
18
77.188
0.08
1.09
1.01
1.2256
0.35
0.27
0.3276
0.8980
8
20
85.764
0.10
1.36
1.26
1.2385
0.44
0.34
0.3342
0.9043
Table 1: Tabulated data
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
7.2 Data Analysis
Graph of Drag Coefficient, CD against Rey. No 1.4
Drag Coefficient, CD
1.2 1
Body base facing upstream
0.8 Body base facing downstream
0.6 0.4 0.2 0 0
20
40
60
80
100
Rey. No Figure 7: Graph of Drag Coefficient, CD against Rey. No
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
7.3 Sample Calculation Air density, ρ = 1.204 kg/m3 Given diameter of circular cylinder, d= 0.065 m Air viscosity, μ = 1.825 x
(T = 20 °C)
No 4, Velocity, V = 12 m/s Rey. No.
= =
(
)(
)(
)
= 51.459 k Rigid Rod Drag Force, FD
= 0.02 N
Body base surface facing upstream Drag Force, FD = 0.48 N Net Drag Force, FD
=
-
= 0.48 – 0.02 = 0.46 N Drag Coefficient, CD
= =
⁄ ⁄ (
)(
) (
)
= 1.2559 Body base surface facing downstream Drag Force, FD Net Drag Force, FD
= 0.15 N =
-
= 0.15 – 0.02 = 0.13 N Drag Coefficient, CD
= =
⁄ ⁄ (
)(
) (
)
= 0.3549
Net Drag Coefficient, CD
= 1.2559 – 0.3549 = 0.9010 Page | 13
THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
8.0
Discussion
This part of report is individually hand written. The result of each member is attached with this report.
9.0
Conclusion
This part of report is individually hand written. The result of each member is attached with this report.
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THERMODYNAMICS II DRAG FORCE IN FLOW OVER A BODY EMD5M5A
10.0 References and appendices Books 1) Cengel, Y. A. & Cimbala, J. M. (2006). Fluid Mechanics. (First Edition). New York: McGraw Hill. 2) Frank M. White, Fluid Mechanics, 5th Edition, Mc Graw Hill, New York, USA, 2003.
Websites 1. Drag equation : http://en.wikipedia.org/wiki/Drag_equation [Accessed 30/10/14]
2. Definition of drag : http://en.wikipedia.org/wiki/Drag_(physics) [Accessed 30/10/14] 3. Applications of drag force : http://www.tandfonline.com/doi/abs/10.1080/15715124.2006.9635283#.VFIXcfmUcwI
[Accessed 30/10/14]
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