Transcript Lecture11 - Lcgui.net

Measurements in Fluid Mechanics
058:180:001 (ME:5180:0001)
Time & Location: 2:30P - 3:20P MWF 218 MLH
Office Hours: 4:00P – 5:00P MWF 223B-5 HL
Instructor: Lichuan Gui
[email protected]
http://lcgui.net
Lecture 11. Wind tunnel, water tunnel and towing tank
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Controlled fluid flow systems
Wind tunnels
Suction wind tunnel
- straight-line, open-circuit arrangement
- honeycomb & screens before contraction
- diffuser to reduce kinetic-energy loss
- fluid mover (fan) located downstream
Blowing wind tunnel
- straight-line, open-circuit arrangement
- fluid mover (fan) positioned upstream
- settling chamber to reduce turbulence
- honeycomb & screens before contraction
- diffuser to reduce kinetic-energy loss
Close-circuit wind tunnel
- higher power efficiency
- reduced noise level
- better flow management
- most large wind tunnels
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Specialized wind tunnels
Open-test-section wind tunnels - to avoid wall effects
a. closed test section
(1) model
(2) Nozzle (contraction)
(3) diffuser
(4) stream of gas flowing from the nozzle
b. open test section
(5) Eiffel chamber
(6) working section
c. open working section with Eiffel chamber
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Specialized wind tunnels
High-speed wind tunnels
- compressible air flow tests
- transonic, supersonic, and hypersonic tunnels
e.g. Two compressed-air wind tunnels
(1) high-pressure compressor
(2) air drier
(3) high-pressure gas tank
(4) throttle valves
(5) nozzle receiver
(6) nozzle
(12) fast-acting valve
(7) model
(13) vacuum gasholder
(8) diffuser
(14) vacuum pump
(9) ejectors
(15) air preheater
(10) throttle valves
(16) radiator
(11) diffuser
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Specialized wind tunnels
Pressurized wind tunnels - to increase air density for high Reynolds number tests
Cryogenic wind tunnels
- reduced air viscosity at low temperature for high Re
Meteorological wind tunnels
- for wind engineering studies
Low-temperature wind tunnels - for the study of low-temperature flow phenomena
Combustion wind tunnels - for high-temperature flows
Shock tubes
(1) high-pressure section
(6) nozzle
(2) low-pressure section
(7) working section
(3) membrane
(8) tank
(4) shock wave
(9) model
(5) contact surface
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Controlled fluid flow systems
Water tunnels
- close-circuit flow systems
- include components:
Pump
settling chamber
contraction
test section
diffuser
- entirely enclosed facilities
Water channels or flumes
- with free surface
Towing tanks
- relative flow w. carriage motion
- lower power consumption
- lower free-stream disturbance
- no boundary-layer effects
- free surface with waves
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Controlled fluid flow systems
Surface waves
red dot: phase velocity, green dots: group velocity
Plunger wave maker
- wave frequency (fw) & wave height (H)
determined by plunger motion
0.8 (m)
0.5 (m)
- wave length ()
𝜆=
0.7 (m)
𝑔
2𝜋ℎ
𝑡𝑎𝑛ℎ
2𝜋𝑓𝑤
𝜆
0.7 (m)
h – depth of the channel
Plunger wave makers
Plunger
- encounter frequency w. model speed Uc
𝑈𝑐
𝑓𝑒 = 𝑓𝑤 +
𝜆
- phase speed of the waves
𝑐𝑝 =
𝜆
= 𝑓𝜆
𝑇
- group speed of the waves
𝑐𝑔 =
𝜕𝜔
𝜕𝑘
 – angular frequency
k – wave number
Regular head waves
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Homework
- Read textbook 6.4-6.7 on page 154-165
- Prepare for midterm test on 09/19
1. look through text notes
2. read related text
3. review homework asignments
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