DRAG FORCE REPORT

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1.0 Title

MEC 554-THERMALFLUIDS LAB

THERMODYNAMICS II LAB

DRAG IN FORCE LAYER OVER A

BODY

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2.0 Abstract

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

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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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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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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.

The drag coefficient (commonly 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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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).

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Page | 8 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)

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6.0 Experimental Procedures

6.1 Apparatus and experiment set up

Figure 6: Sub sonic wind tunnel

Figure 4: Weight balance Figure 3: Rigid rod and Hemisphere with body base facing downstream and upstream

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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

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7.0 Results

7.1 Data recorded No Velocity (m/s) Rey. No. (x103) Rigid Rod Drag Force, FD (N)

Body base surface facing upstream

Body base surface facing downstream Net Drag Coefficient, CD Drag Force, FD (N) Net Drag Force, FD (N) Drag Coefficient, CD (N) Drag Force, FD (N) Net Drag Force, FD (N) Drag Coefficient, CD (N) 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

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Page | 12 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 20 40 60 80 100 D rag Co e ff ic ie n t, CD Rey. No

Graph of Drag Coefficient, C

D

against Rey. No

Body base facing upstream

Body base facing downstream

7.2 Data Analysis

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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 = 0.15 N

Net Drag Force, FD = -

= 0.15 – 0.02 = 0.13 N Drag Coefficient, CD = _⁄

= _{⁄ ( )( )} _{( )} = 0.3549

Net Drag Coefficient, CD = 1.2559 – 0.3549

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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

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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