lecture # 3: wind tunnels and water tunnelsopen circuit wind tunnel • suction wind tunnel: with...

Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved!

Dr. Hui Hu

Dr. Rye Waldman

Department of Aerospace Engineering

Iowa State University

Ames, Iowa 50011, U.S.A

Lecture # 3: Wind Tunnels and Water Tunnels

AerE 344 - Lecture Notes

Sources/ Further reading: Barlow, Rae, & Pope, “Low-speed wind tunnel testing,” Ch 2 & 3


Measurement uncertainty example

Suppose a measurement has a true value of 0.5 and a measurement uncertainty of +/- 0.1. >> x = 0.5 + 0.1*randn([1,225]);

•Compute the standard deviation of the data >> std(x)

0.0930

•Compute the mean of the first n samples >> n = 1:length(x);

>> mean_n_x = cumsum(x) ./ n;

•Compare the “error” to the standard deviation

divided by the sqrt(number of samples) for the first n

samples >> for i = 1:length(x),

>> er(i) = mean_n_x(i)-mean(x);

>> u(i) = std(x(1:i))/sqrt(n(i));

>> end


Function of Wind Tunnels and Water Tunnels

• Producing the desired flow field with controlled conditions

http://www.solarnavigator.net/propellers.htm


Function of Wind Tunnels and Water Tunnels

Wind tunnel vs water tunnel testing

ReUd

-5

3

2-5

kg1.2 , 1.85 10 Pa•s

m

m1.5 10

s

-3

3

2-6

kg1000 , 1.00 10 Pa•s

m

m1.0 10

s

2

FF U C

3

PP U C

Air:

Water:

Power:

Force:


Types of Wind Tunnels

Based on Flow Speed:

• Subsonic or low speed wind tunnels (M<<1.0)

• Transonic wind tunnels (M1.0)

• Supersonic wind tunnels (1.0 <M<5.0)

• Hypersonic wind tunnels (M>5.0)

Based on Shape:

• Open circuit wind tunnel

• Closed circuit wind tunnel


Open Circuit Wind Tunnel

• Suction wind tunnel: With the inlet open to atmosphere, axial fan or

centrifugal blower is installed after test section.

• Blow down wind tunnel: A blower is installed at the inlet of wind tunnel

which throws the air into wind tunnel.


Closed circuit wind tunnel


Components of a Wind Tunnel

• Test section

• Contraction section

• Diffuser section

• Setting chamber

• Screens and similar structures

• Cooling system/radiators

• Motor/fans


Function of Contraction

Va

ΔVa~10%

ΔVb =?

Vb a

b

Ac

A

Aa

Ab



Va

ΔVa

ΔVb =?

a

b

Ac

A

2

2 2

2 2

1

2

1 1

2 2

1( 1)

2

x x

a a b b

b a a

p V const

p V p V

p p V c

a a b b

b a

V A V A

V cV

Aa Ab

ΔVb

Mass cons:

Bernoulli:

At the perturbation:

2 2 2 2

2 2 2

2 2 2 2

1 1 1( ) ( 1) ( )

2 2 2

1 1( 2 ) ( 2 )

2 2

2 2

a a a a a b b

a a a b b b

a a a a a b

p V V p V c V V

c V V V V V V

c V V V c V cV V

bp



Va

ΔVa

ΔVb =?

a

b

Ac

A

2

2 2

2 2

1

2

1 1

2 2

1( 1)

2

x x

a a b b

b a a

p V const

p V p V

p p V c

a a b b

b a

V A V A

V cV

Aa Ab

ΔVb

Mass cons:

Bernoulli:

At the perturbation:

2 2 2 2

2

2 2

1

a a a a a b

a a a b

a a a b a b

a b a b

c V V V c V cV V

V V cV V

V V cV V V V

cV V c V V



Va

ΔVa~10%

ΔVb =?

Vb a

b

Ac

A

2

1 0.10.001

100

b a

b a

V V

V c V

0.1a

b

Vif

V

Aa

Ab

2

1 a b

a b

V V

c V V


Water Tunnels


Towing Tank


Test section, T

Contraction

section

A

E

V

Settling

chamber

Lab#02: Wind Tunnel Calibration

A A A E E E T T TV A V A V A

Total pressure:

At points A and E:

Here, pressure at A and E related by loss

coefficient C1:

Mass conservation:

Assume:

Then:

2

0 0 0

1

2p V P

2 2

0 0

0 0

1 1,

2 2A A A E E E

E A

p V P p V P

P P

2 2 2

1

0 01

2

1 1 1

2 2 2

1

2

A E E E A

A E

E

p p V V C V

P PC

V

A E T

A A E E T TV A V A V A

Can write:

2 2 21 1 1

2 2 2A A A E E E T T TV A V A V A


2

2

1*

*

VC

qC

ppp

T

EA

Test section

Contraction

section

A

E

V

Settling

chamber


For dynamic pressure q, e.g.,

rewrite:

as

Arrange as and .

Define such that

Then

Becomes

21

2A A Aq V

2 2 21 1 1

2 2 2A A A E E E T T TV A V A V A

2 2 2

A A E E T Tq A q A q A

2

2

EA E

A

Aq q

A

2

2

TE T

E

Aq q

A

2 2

2 32 2, E T

A E

A AC C

A A 3

2 3 2

,E T

A E T

q q C

q q C q C C

1A E E E Ap p q q C q

3 3 1 3 2

3 1 2(1 )

A E T T T

AE T

p p q C q C C q C C

p q C C C


2

2

1*

*

VC

qC

ppp

T

EA

Contraction

section

A

E

V

Settling

chamber

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120 140

Linear curve fittingExperimental data

P = PA-P

E (Pa)

q =

0.5

*V

2


Test section, T


Before you do the Labs…

• Choose 1~2 member as the Lead Operators

• Bring you own flash drive for the data storage.

• Do not touch other research equipment in the wind tunnel laboratory.

• Keep the wind tunnel laboratory clean and organized.

lecture # 3: wind tunnels and water tunnelsopen circuit wind tunnel • suction wind tunnel: with...

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