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A brand-new edition of the classic guide on low-speed wind tunnel testing While great advances in theoretical and computational methods have been made in recent years, low-speed wind tunnel testing remains essential for obtaining the full range of data needed to guide detailed design decisions for many practical engineering problems.
- Shown in Figure 2.3. The Lockheed low-speed wind tunnel has tandem test sections with two contractions. The first, and larger, test section is for V/STOL or powered lift models and has a cross-sectional area of 780 fr2with speeds from 23 to 115 mph. The second test section has a cross section of 378 ft 2 and speeds from 58 to 253 mph.
- LOW-SPEED WIND TUNNEL TESTING BY JEWEL B. BARLOW, WILLIAM H. RAE, ALAN POPE PDF. A brand-new edition of the classic guide on low-speed wind tunnel testing While great advances in.
Floor plan of Eiffel's 1912 laboratory at Auteuil, Paris, with two open-return wind tunnels
- 1Subsonic tunnel
Subsonic tunnel[edit]
Low-speed wind tunnels are used for operations at very low Mach number, with speeds in the test section up to 480 km/h (~ 134 m/s, M = 0.4) (Barlow, Rae, Pope; 1999). They may be of open-return type (also known as the Eiffel type, see figure), or closed-return flow (also known as the Prandtl type, see figure) with air moved by a propulsion system usually consisting of large axial fans that increase the dynamic pressure to overcome the viscous losses.
Open wind tunnel[edit]
Schematic of an open wind tunnel with a closed test section
Thermodynamics pressure problems. The working principle is based on the continuity and Bernoulli's equation:
The continuity equation is given by:
The Bernoulli equation states:-
Putting Bernoulli into the continuity equation gives:
Wind Tunnel Testing Test Section
The contraction ratio of a windtunnel can now be calculated by:
![Low Speed Wind Tunnel Testing Barlow Pdf To Excel Low Speed Wind Tunnel Testing Barlow Pdf To Excel](/uploads/1/2/4/7/124790955/597618160.png)
Closed wind tunnel[edit]
Schematic of a closed (return-flow) wind tunnel
In a return-flow wind tunnel the return duct must be properly designed to reduce the pressure losses and to ensure smooth flow in the test section.The compressible flow regime:Again with the continuity law, but now for isentropic flow gives:
The 1-D area-velocity is known as:
The minimal area A where M=1, also known as the sonic throat area is than given for a perfect gas:
Transonic tunnel[edit]
High subsonic wind tunnels (0.4 < M < 0.75) and transonic wind tunnels (0.75 < M < 1.2) are designed on the same principles as the subsonic wind tunnels. The highest speed is reached in the test section. The Mach number is approximately 1 with combined subsonic and supersonic flow regions. Testing at transonic speeds presents additional problems, mainly due to the reflection of the shock waves from the walls of the test section (see figure below or enlarge the thumb picture at the right). Therefore, perforated or slotted walls are required to reduce shock reflection from the walls. Since important viscous or inviscid interactions occur (such as shock waves or boundary layer interaction) both Mach and Reynolds number are important and must be properly simulated.Large-scale facilities and/or pressurized or cryogenic wind tunnels are used.
de Laval nozzle[edit]
With a sonic throat, the flow can be accelerated or slowed down. This follows from the 1D area–velocity equation. If an acceleration to supersonic flow is required, a convergent-divergent nozzle is required.Otherwise:
- Subsonic (M < 1) then converging
- Sonic throat (M = 1) where
- Supersonic (M >1 ) then diverging
Low Speed Wind Tunnel Testing Barlow Pdf To Excel Free
Conclusion: The Mach number is controlled by the expansion ratio Sempre caro marcello fois.
See also[edit]
- National Aerospace Laboratory, Netherlands
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Subsonic_and_transonic_wind_tunnel&oldid=799290591'
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