A wind tunnel is a facility that provides a controlled airflow for testing aerodynamic models. It has a test section where models are placed and sensors measure forces like lift and drag. Wind tunnels are classified based on speed of airflow, air pressure, and size. They can have open or closed designs and use various flow visualization techniques to study airflow patterns.

1. Gayon, Jio RossGayon, Jio Ross
Godfrey S.Godfrey S.
Oarde, Kevin Victor L.Oarde, Kevin Victor L.
Zaide, John Chester A.Zaide, John Chester A.
Wind TunnelWind Tunnel

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Frank WenhamFrank Wenham
Benjamin RobinsBenjamin Robins
George CayleyGeorge Cayley
Osborne ReynoldsOsborne Reynolds
Hiram MaximHiram Maxim
Wright BrothersWright Brothers

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IntroductionIntroduction
What is a Wind Tunnel?
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Introduction Classifications Elements Types Shapes Flow Visualization
 a facility that provides a controllable
flow field for investigating various flow
phenomena and testing aerodynamic
models
 a tool used in aerodynamic research
to study the effects of air moving past
solid objects
*** Advantage: experiments can be performed under well-controlled
flow circumstances compared to open environment experiments

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National Full-Scale Aerodynamics Complex ,
NASA Ames Research Center, United States

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Aeronautical Wind Tunnels
Automobile Tunnels
Aeroacoustic Tunnels
Classifications of Wind TunnelClassifications of Wind Tunnel
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Aeronautical Wind TunnelsAeronautical Wind Tunnels
High Reynold’s Number Tunnels
Pressurized Tunnels
Heavy Gas Tunnels
Cryogenic Tunnels
High-altitude Tunnels
V/STOL Tunnels
Spin Tunnels
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Tunnels are also classified by flow speed:
Subsonic (M<.8),
Transonic (.8<M<1.2),
Supersonic (1.2<M<5.0), or
Hypersonic (M>5.0)
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Wind tunnels may also be classified according to their
air pressure:
atmospheric
variable- density
or their size:
ordinary
full-scale
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Elements of aElements of a
Wind TunnelWind Tunnel
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 straightens the airflow
*** The less turbulence there is, the
better the wind tunnel will simulate
actual flying conditions
 usually includes a honeycomb flow
straightener and wire mesh
smoothing screens that produce a
smooth airflow; effective at reducing
swirling currents in the tunnel airflow
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*** purpose: take a large volume of low-velocity
air and reduce it to a small volume of high-
velocity air
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 models of wings or planes are placed here
*** As airflow is brought to the
desired velocity, sensors measure
forces, such as lift and drag, on the
test article.
Lift is the force on the wing opposite the force of gravity.
Lift holds a plane in the air.
Drag is the force on the wing in the direction of the
airflow. An engine must overcome this force to move a
plane through the air.
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Shapes of Test SectionShapes of Test Section
Rectangular (General Purpose)
Circular (Axisymmetric Model)
Elliptical (Aircraft Model)
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 where the air coming out of the test section
slows down prior to exhausting or
recirculating
 a device to lower the air flow speed,
consequently reduce the pressure loss due
to friction
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 provides the force that causes air to move
through the tunnel
*** Fan drive: provide a
pressure increase of
flow, to overcome the
pressure loss in the
tunnel circuit.
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Types of Wind TunnelTypes of Wind Tunnel
Closed-type
Open-type
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Blowdown
Shock Tube

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Open-type Wind TunnelOpen-type Wind Tunnel
 also called an Eiffel tunnel
 open on both ends and draws air
from the room into the test section
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AdvantagesAdvantages
Low construction cost.
Superior design for propulsion and smoke
visualization. There is no accumulation of exhaust
products in an open tunnel
DisadvantagesDisadvantages
Poor flow quality possible in the test section
High operating costs
Noisy operation
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Closed-type Wind TunnelClosed-type Wind Tunnel
 also called an Prandtl tunnel or Gottingen tunnel
*** Air is conducted from the exit of the test section
back to the fan by series of turning vanes; air is
returned to the contraction section and back to the
test section; air is continuously circulated
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AdvantagesAdvantages
Superior flow quality in the test section
Low operating costs
Quiet operation
DisadvantagesDisadvantages
Higher construction cost
Inferior design for propulsion and smoke visualization
Hotter running conditions than an open return tunnel
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has a high pressure vessel upstream of the test
section and a low pressure reservoir downstream
of the test section
used for supersonic testing.
Blowdown Wind TunnelBlowdown Wind Tunnel
used for hypersonic testing
Shock TubeShock Tube
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AdvantagesAdvantages
High Mach capability
Lower construction and operating costs.
Superior design for propulsion and smoke visualization
Smaller loads on model during startup because of faster
starts
DisadvantagesDisadvantages
Shorter test times require faster (often more expensive)
instrumentation.
Need for pressure regulator valves.
Noisy operation.
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used to study aerodynamic flow under a wide
range of temperatures and pressures that are difficult
to obtain in other types of testing facilities;
are also used to investigate compressible flow
phenomena and gas phase combustion reactions
Shock TubeShock Tube
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Flow VisualizationFlow Visualization
 aids the people to see the movement of air while
inside the wind tunnel
 used to make the flow patterns visible

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Qualitative
Smoke
Tufts
Evaporating Suspensions
Oil
Fog
Sublimation
Quantitative
Particle Tracking Velocimetry
Particle Image Velocimetry
Laser Speckle Velocimetry
Optical
Shadowgraph
Schlieren Photography
Interferometry

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Shadowgraph-
Schlieren Photography
Inferometry
Optical MethodsOptical Methods

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Smoke-
Tufts-
Oil-
Qualitative MethodsQualitative Methods
Evaporating Suspensions
Fog-

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Quantitative MethodsQuantitative Methods
Particle Tracking Velocimetry
Particle Image Velocimetry
Laser Speckle Velocimetry