1 | P a g e

TITLE PAGE.

DRAG FORCES ON BLUFF AND

STREAMLINED BODIES UNIVERSITY OF

BOLTON.

MSP4000 ENGINE SYSTEMS &

AERODYNAMICS

6TH

AND 7TH

OF MAY 2015.

DR RAJ PERERA.

AKINWUMIJU BENJAMIN OLUWASEGUN 20277275.

FD. MOTORSPORTS TECHNOLOGY.

2 | P a g e

ABSTRACT.

1.1 Title page.

1.2 Table of Content.

1.3 Introduction.

1.4 Main Body.

1.5 - 1.7 Table of Values.

1.8 - 4.2 Graph Table for each object used.

4.3 – 4.7 Comparisons of Each object used.

4.8 Recommendation.

4.9 Evaluation.

5.0 Appendices and References.

3 | P a g e

TABLE OF CONTENT.

(1) INTRODUCTION. (Page 4).

(2) THE MAIN BODY. (Page 5 to 43).

(3) RECOMMENDATION. (Page 44).

(4) EVALUATION. (Page 45).

(5) APPENDICES. (Page 46 - 48).

(6) REFERENCES. (Page 49).

4 | P a g e

INTRODUCTION.

A wind tunnel is a device used in aerodynamic research to study the effects of air

moving around a solid object, in order to know how such an object can withstand the

flow of air when it is moving through it. This test is carried out by placing or

suspending the object in the middle of the tunnel. Air is made to move past the object

by powerful fan system in other to know how the forces of air affects the object.

While this is done a careful measurement of the forces of the air is taken so as to

understand and improve on the performance of the very object before the final

production. Tunnels are designed for different purposes and speed ranges differs.

There are various forms of wind tunnels for example;

1. Subsonic, Closed Return.

2. Water Tunnel.

3. Subsonic Open Return Full Scale.

4. Supersonic Closed Return Propulsion.

5. Subsonic Open Return Smoke Tunnels.

5 | P a g e

THE MAIN BODY.

This is the report of the exercise carried out at the University of Bolton, the exercise

was carried out on a wind tunnel device in order to know and understand the

theories of aerodynamics, the effects of drag forces on bluff and streamlined bodies.

To achieve this we need to take a look at the drag and lift, side forces and how

Bernoulli’s equation for pressure is applied to aerodynamics. Before the activity was

carried out here are few of the equipment used for the experiment; (1) C15-10 Wind

Tunnel with IFD7 (2) PC running system software. (3) C15-22 Drag Models. (4) C15-

13 Lift and Drag balance. (5)C15-15 Wake Survey Rake. The wind tunnel still need a

fan and bell mouth in order to work.

The wind tunnel is operated by a fan which is connected to one end of the tunnel.

What the fan does is to help in sucking air into the tunnel from the Bellmouth, the air

drawn in by the fan exits the tunnel into the room then the air will be recirculated

back into the Bellmouth. The recirculation helps in keeping the flow of air in

uniformity order during the test section. The fan is turned by a large electrically

powered drive motor. The Bellmouth is the other end of the wind tunnel where air

flows through into the tunnel, the Bellmouth has an air straight liners which are built

in the form of honeycomb, what this does is to help in straitening up of the air in the

tunnel. When all this are in place then one can go straight into the text section.

The wind tunnel that was used in carrying out the exercise was a computer

controlled subsonic wind tunnel. I started by making sure that the fan is set to zero

and also all other manometer readings are on zero velocity, then follow by selecting

the percentage to start the experiment from, select the body fitted to drag balance in

the selection box. Then the experiment can take place by increasing the fan rotation

according to the instructions given.

The following bodies were used in carrying out the experiment;

(1) Circular Disk.

(2) Concave Hemisphere.

(3) Convex Hemisphere.

(4) Small Dimpled shape.

(5) Small Plain Sphere.

(6) Small Smooth Sphere.

(7) Streamlined Shape.

After testing each of the above named objects different values were obtained for

them all as we have them on the table below.

6 | P a g e

(1)CIRCULAR DISK.

(2)CONVEX HEMISPHERE.

7 | P a g e

(3)CONCAVE HEMISPHERE.

8 | P a g e

(4)SMALL DIMPLED SPHERE.

(6)SMALL PLANE SPHERE.

9 | P a g e

(7)SPHERE.

Then after completing the testing on each of the objects, then i have to compare

each of the object in order to know the rate of flow of air around each of the objects

and also to know the velocity of flow at which the boundary layer behaviour changes

on each of the objects with the help of a graph.

Below are the results and graph of how each of the object behave in the wind tunnel

by plotting the graph of;

(1) Drag against Tunnel Velocity for each object.

(2) Drag against Reynolds Number for each object.

(3) Pressure 1-10 wake survey rake against Reynolds Number for each object.

10 | P a g e

DRAG VS. TUNNEL VELOCITY (1.1) SPHERE.

11 | P a g e

1.2 SMALL DIMPLED SPHERE.

12 | P a g e

1.3 CONVEX HEMISPHERE.

13 | P a g e

1.4 CIRCULAR DISK.

14 | P a g e

1.5 SMALL SMOOTH SPHERE.

15 | P a g e

1.6 STREAMLINED SHAPE.

16 | P a g e

1.7 CONCAVE HEMISPHERE

17 | P a g e

(2) DRAG VS. REYNOLDS NUMBER (2.1) SPHERE.

18 | P a g e

2.2 SMALL DIMPLED SPHERE.

19 | P a g e

2.3 CONVEX HEMISPHERE.

20 | P a g e

2.4 CIRCULAR DISK.

21 | P a g e

2.5 SMALL SMOOTH SPHERE.

22 | P a g e

2.6 STREAMLINED SHAPE.

23 | P a g e

2.7 CONCAVE HEMISPHERE.

24 | P a g e

(3)SURVEY RAKE VS. REYNOLDS NUMBER (3.1) SPHERE

25 | P a g e

26 | P a g e

3.2 SMALL DIMPLED SPHERE.

27 | P a g e

28 | P a g e

3.3 CONVEX HEMISPHERE.

29 | P a g e

30 | P a g e

3.4 CIRCULAR DISK.

31 | P a g e

32 | P a g e

3.5 SMALL SMOOTH SPHERE.

33 | P a g e

34 | P a g e

3.6 STREAMLINED SHAPE.

35 | P a g e

36 | P a g e

3.7 CONCAVE HEMISPHERE.

37 | P a g e

Below are the list of the of the various objects used for the experiment;

(1) Small Plain Sphere.

(2) Small Dimpled Sphere.

38 | P a g e

(3) Convex Hemisphere.

(4) Circular Disk.

(5) Small Smooth Sphere.

(6) Streamlined Shape.

(7) Concave Hemisphere.

On each of the above models mounted inside the wind tunnel they all have different

boundry layer transition which transfers from a laminar flow to a turbulent flow. After

completing the experiment the following observations were noted on each of the

models.

(A)STREAMLINED.

The boundary layer of a streamlined shape was more turbulent and has the highest

turbulent flow on the boundry layer.

(B)Convex Hemisphre

Then folow by convex hemisphere shape which is next to the streamlined body in

terms of turbulence, though with very little difference in their boundary layer.

39 | P a g e

(C)SPHERE.

Amont all other objects the sphere has the highest turbulent air flow in its boundry

layer compare to the two above mentioned models, (Streamlined & Hemisphere

Shape) and every other objects used.

(D) SMALL SMOOTH

After the ones above is the small smooth sphere which has less turbulent in its

boundry layer compare to the two above mentioned models, (Streamlined, Convex

Hemisphere & Sphere Shape).

40 | P a g e

(E)SMALL DIMPLED.

The small dimpled sphere has a lesser turbulent flow of air around its boundary layer

though very close to that of the small smooth sphere.

(F)CIRCULAR DISK.

The cirular Disk has close result of turbulent flow of air with the convex in bounbary

layer compare to the other mounted objects above.

41 | P a g e

Below is the list of the objects mounted according to how turbulent the air flow

around them is.

(1) . The Sphere Shape, which is the object with the highest turbulent air flow

around its boudary layer

(2) The Streamlined Shape.

(3) The convex Hemisphere.

(4) The circular Disk

(5) Concave Hemisphere.

(6) The Small Dimpled Sphere.

(7) The Small Smooth Sphere.

The boundary layer is the immeidate surrounding part of the object in which the

laminar and the turbulent air flowing around the object can be viewed whenever they

are undergoing any form of layer transition. Laminar flow is a streamlined air that

flows in a parallel layer, when the air is travelling at low velocity around the object,

there will not be lateral mixing of air in the flow like swirls or vortex.

Turbulent flow. In this case the turbulent air flowing are not going to be in an orderly

manner but very rough air flow with lateral mixing of vortexes which can be viewed

behind the body in which the air is travelling around. Whenever the Renolyds

number of any flow is less that 2000, it is a laminar flow and when the flow is higher

than 4000, it is a turbulent flow.

The Bernoulis equation is used in calculating the lift on an aerofoil weather tehre is a

high or a low pressure on a surface. Which is given by; NR = 𝑉𝐷𝑒

𝑛 =

𝑉𝐷

𝑉

42 | P a g e

NR = RENOLDS NUMBER.

V = VELOCITY OF FLOW (m/s).

D = DIAMETER OF PIPE (m).

e = DENSITY OF WATER (kg/𝑚3 ).

n = DYNAMIC VISCOCITY (kg/m.s).

V = KINEMATIC VISCOCITY (𝑚2 /s).

After all this was done, I could see that as the flow rate of air increases, a vortex is

created in which swirling air creates a heavy drag on most of the objects used due to

their shapes but lesser drags on Circular Disk and the Small Dimpled Sphere. The

higher the speed of the fan, the higher the drag and the higher the Reynolds

Number, as we can see from the data we have on the table for the experiment, each

object has a high reynolds numbers at high fan speeds.

In comparism, Small Smooth Sphere and a Small Dimpled Sphere.

In a Small Smooth Sphere, the type of air that flows around the ball is a laminar flow,

the shape and surface of the ball quickly separate air from the ball thereby producing

a vortex, the swirling air around the ball then creates a heavy drag which reduces the

rate at which the smooth small ball can travel through the air.

43 | P a g e

Then in a Small Dimpled Sphere, the dimples around the ball surface helps the ball

in creating a form of turbulence air that flows around the ball. The turbulence sucks

air to the ball and separate from it at a low rate thereby producing a smaller vortex

and very less drag, so the rate at which the dimpled ball is going to travel through the

air will be higher and farther than a small smooth ball due to its dimpled surface. So

the turbulent air around the boundary layer of a small smooth sphere will be more

higher than the air we are going to get around the boundary layer of a small dimpled

ball due to their body surface and the amount of turbulent air flow they produce.

The effect of the supporting rod on the result of the model mounted was that; the

supporting rod will increase the rate of drag thereby making the air travelling around

the model mounted and the rod more turbulent. That is the more drag you get the

turbulent the air, unlike when the object is been suspended in the air, the result you

will have for the air flowing around the object is going to be a laminar flow with a

lesser drag. The rate of flow of the air around the object can be determined by

adding smoke or dye into the air flowing or by attaching a Yarn-like strand in the air

which can also be attached to the mounted model in the tunnel which will make the

flow very visible when caring out the experiment.

44 | P a g e

RECOMMENDATION.

At the end of this experiment, I adviced that before the final production of any object

that will be travelling through the air,such an object needs to be tested in wind

tunnels in order to know how the object can withstand air pressure whenever is

acting on it. And more so the wind tunnel will help the person producing the object to

know where to make the necessary corrections and the best shape with the surface

to be used in designing such an object. This means that at the end of the final

production the money spent will not be wasted. Instead of studying the object or the

material which as not been tested in the wind tunnel then now trying to make the

corrections after it has been finaly produced. Wind tunnels are made for different

purposes and sizes depending on what to be tested so the cost of production have

always been the problem.

45 | P a g e

EVALUATION.

A wind tunnel is a device used in aerodynamic research to study the effects of air

moving around a solid object, in order to know how such an object can withstand the

flow of air when it is moving through it and also to understand the theories of

aerodynamics, the effects of drag forces on bluff and streamlined bodies.

The wind tunnel is operated by a fan which is connected to one end of the tunnel, the

fan helps in drawing in air into the tunnel from the Bellmouth, then passes out the air

from the other end of the tunnel into room and recirculated it into the tunnel in order

to have uniform flow of air into the wind tunnel during the test section. On each of the

used as the flow rate of air increases, a vortex is created in which swirling air creates

a heavy drag on most of the objects used due to their shapes so the higher the

speed of the fan, the higher the drag and the higher the Reynolds Number. The

major effect of the supporting rod is that it will increase the rate of drag thereby

making the air travelling around the model mounted and the rod more turbulent.

After all this was done, I could see that as the flow rate of air increases, a vortex is

created in which swirling air creates a heavy drag on most of the objects used due to

their shapes but lesser drags on Circular Disk and the Small Dimpled Sphere. The

higher the speed of the fan, the higher the drag and the higher the Reynolds

Number, as we can see from the data we have on the table for the experiment, each

object has a high reynolds numbers at high fan speeds.

46 | P a g e

APPENDICES.

Taken the readings of the objects mounted.

47 | P a g e

Remounting another object into the tunnel.

Images of the object used.

48 | P a g e

49 | P a g e

REFFERENCES.

(1) Aerospace engineering and manufacturing, march 2009. Pp 27-28 society of

Automotive engineering.

(2) Dodson, MG (2005) An Historical and Applied Aerodynamic study of the

Wright Brother’s Wind Tunnel Test program and Applications to Successful

Manned flight US Naval Academy Technical Report. USNA-334. Retrieved

2009-03-11.

(3) www.quora.com/At-what-application-turbulent.flow-regime-is-prefarable-and-

why.