lecture # 3: wind tunnels and water tunnelsopen circuit wind tunnel • suction wind tunnel: with...
TRANSCRIPT
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
Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
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
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Function of Wind Tunnels and Water Tunnels
• Producing the desired flow field with controlled conditions
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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:
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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
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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.
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Closed circuit wind tunnel
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Components of a Wind Tunnel
• Test section
• Contraction section
• Diffuser section
• Setting chamber
• Screens and similar structures
• Cooling system/radiators
• Motor/fans
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Function of Contraction
Va
ΔVa~10%
ΔVb =?
Vb a
b
Ac
A
Aa
Ab
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Function of Contraction
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
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Function of Contraction
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
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Function of Contraction
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
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Water Tunnels
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Towing Tank
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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
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2
2
1*
*
VC
qC
ppp
T
EA
Test section
Contraction
section
A
E
V
Settling
chamber
Lab#02: Wind Tunnel Calibration
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
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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
Lab#02: Wind Tunnel Calibration
Test section, T
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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.