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Nagle College
Physics U2 Wind Tunnels
1. Different common fluid Tunnels
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Open return wind tunnel
Closed return wind tunnel
Hypersonic wind tunnel
Water tunnel
Plasma tunnel. .............
2. Open return wind tunnel
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Low speed (subsonic), velocity of fluid flow v < 0.8M and usually v ≈ 130 m/s
A tube with a fan and a test section. It is usually a circular tube, which will have
less chance to create turbulence flow.
3. Closed return wind tunnel
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Low speed (subsonic). This type of wind tunnel can be used for engineering and
architecture (car, buildings, bridges, city planning, landscape....),
Transonic Velocity ≈ 0.7 M to 1.4 M (M = Mach number = Velocity of a flying
object V/velocity of sound (a) = V/a ).
Supersonic Velocity ≈ 1 M to 5 M
Hypersonic Velocity ≈ 5 M to 15 M or higher.
4. Good points for using wind tunnel
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b.
c.
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Use scaled model to test rather the real subject.
Easy to monitor and modify
Less cost
Safer.
5. Used them to collect data on
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Forces. (Lift, drag and side forces)
Moments. (Yawing, pitching and rolling)
Surface pressures
Surface temperature
Pattern of flowing fluid. (smoke, dye, sand, fluorescent tuft, speed camera...)
6. They can be applied on the models of
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Planes, car, fast train and watercrafts.....(to measure drag and noise level....)
Building, bridge (to measure cladding pressure, structural loading, eg.
Bending moment, support reactions....)
 Environment and landscape. (pollutant and atmospheric dispersion study)
 Turbine blades and propellers
In some very demanding cases
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Rocket, rocket engine, jet engine, satellite and missile re-entry. (high speedturbulent flow, high temperature, plasma fluid)
Nuclear reactor coolant system- heat transfer. (high temperature, radioactive,
corrosive)
7. Data Collections and Computer Aid Design
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Base on the data collected by wind tunnels, nowadays, people use computer to do
their jobs  CAD (Computer Aided Design), CAM (Computer Aided
Manufacturing), CADKEY, KEYCREATOR, CNC (Computer Numerical Control),
CAE (Computer Aid Engineering)...............
The model design will be easier and cheaper. However, it will be limited in the
existed collected data. In some cases, it cannot replace the wind tunnels.
8. In the test section of a wind tunnel
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Mass of fluid in = mass of fluid out
Mass m = ρVA = density x Velocity x cross sectional area
ρ1 V1 A1 = ρ2 V2 A2 = k
9. Energy Ratio
Energy ratio (ER) for closed return wind tunnel ≈ 6 to 10.
ER for open return circuit wind tunnel ≈ 1 to 2
Energy required (KW) = (13.3/ER) (V/100)3 (A ρ)
A = cross sectional area of tested object
ρ = density of fluid.
V= velocity of fluid.
From this ER equation, we know that it needs less energy to run a closed return wind
tunnel than an open return wind tunnel. However, it will be more expensive to build a
closed return wind tunnel than an open return wind tunnel.
10. Diagrams of wind tunnels
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i. A closed return flow wind tunnel is shown as below.
Fan
Test model
contraction
Diffuser
Test section
ii.
A hypersonic wind tunnel
heater
Vacuum
valve
Vacuum
chamber
High
pressure
chamber
model
Pressure
regulator