2. What is a wind tunnel?
Wind tunnels are measurement tools to study gas flows around
a body and the forces generated by the gas-body interaction
Mostly air is used in wind tunnels
Using such tool it is possible to measure global and local flow
velocities, as well as pressure and temperature around the body
3. Components of a wind tunnel
Bell mouth section/Nozzle Fine screen mesh
4. Components of a wind tunnel
Diffuser section with a
Test chamber
Suction fan located at
The left of the diffuser
22. Wind tunnel Design
Settling chamber
Settling chamber consists of honeycombs and mesh screen to
reduce the flow turbulence before it enters the nozzle.
27. Wind tunnel Design
Settling chamber: screens
To have effective reducing in
turbulence the porosity must
lie between 0.58 to 0.8
Different mesh qualities
(coarse, medium, f ine)
are efficient than single fine
mesh
28. Wind tunnel Design
Pressure losses
1) Pressure loss in constant cross section area sections (friction)
2) Pressure loss in diffusers (friction and expansion)
3) Pressure loss in corners (friction and expansion)
4)Pressure loss in screens(porosity or its complement solidity, the Reynolds number
Calculated with wire diameter, and mesh factor)
5) Pressure loss in honeycombs (length to cell hydraulic diameter ratio,
porosity and Reynolds number)
6) Pressure loss in nozzles (skin friction)
30. Summary
The design procedure consists of the following main steps:
1. Defining the test section dimensions and desired flow velocity by test type;
2. Wind tunnel component design by test section criteria;
3. Wind tunnel component pressure loss calculation;
4. Determining pressure loss throughout the wind tunnel circuit as a function
of the possible flow velocity in the testing section in both open and closed
configurations;
5. Matching wind tunnel components to commercial fans, and energy
considerations.
31. References:
1)Justin D Periera, “Wind tunnels-Aerodynamics, models and experiments”,
Nova science publishers
2) Metha R. D., Bradshaw P. “Design Rules for Small Low Speed Wind Tunnels”
Journal of Royal Aeronautical Society 1979, Vol. 73.
3)Wind tunnel design and wind tunnel parts-NASA
Editor's Notes
If the test chamber length is more than 3 times of hyddia, then the boundary layer thickness increases. If the test chamber length is less than 0.5 times of hyddia, boundary layer thickness is too short