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Types of Wind Tunnels

Types of Wind Tunnels. Subsonic Transonic Supersonic Hypersonic Cryogenic Specialty Automobiles Environmental- Icing, Buildings, etc. Subsonic Wind Tunnels. 40’ x 80’ and 80’ x 120’ NASA Ames. 40- by 80- Foot Wind Tunnel: Specifications Primary Use:

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Types of Wind Tunnels

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  1. Types of Wind Tunnels

  2. Subsonic Transonic Supersonic Hypersonic Cryogenic Specialty • Automobiles • Environmental- Icing, Buildings, etc.

  3. Subsonic Wind Tunnels

  4. 40’ x 80’ and 80’ x 120’ NASA Ames

  5. 40- by 80- Foot Wind Tunnel: Specifications • Primary Use: • The facility is used primarily for large-scale or full-scale testing of aircraft and rotorcraft, including high-lift and noise suppression development for subsonic and high speed transports, powered lift, high angle-of-attack for fighter aircraft and propulsion systems • Capability: • Mach Number: 0-0.45 • Reynolds Number per foot: 3 X 106 • Stagnation Pressure: Atmospheric • Temperature Range: 485 ° - 580 ° R • Closed circuit, single return, continuous flow, closed throat wind tunnel with low turbulence • Model-support systems available include a 3 strut arrangement with a nose or tail variable height strut, a semi-span mount and a sting • The entire model support can be yawed a total of 290 ° • Six components of force and moment are measured by the mechanical, external balance under the test section, or by internal strain-gage balances in the sting or rotor testbeds • Test section walls are lined with a 10" acoustic lining, and the floor and ceiling have a 6" acoustic lining

  6. 80- by 120- Foot Wind Tunnel: Specifications • Primary Use: • The facility is used primarily for large-scale or full-scale testing of aircraft and rotorcraft, including high-lift development for subsonic transports, V/STOL powered lift, high angle-of-attack for fighter aircraft and propulsion systems • Capability: • Mach Number: 0-0.15 • Reynolds Number per foot: 1.2 X 106 • Stagnation Pressure: Atmospheric • Temperature Range: 485 ° - 580 ° R • Indraft, continuous flow, closed throat wind tunnel

  7. Fans for 40x80 and 80x120

  8. 80’x120; 40’x80’

  9. 12 foot Pressure Tunnel

  10. 12-Foot Pressure Wind Tunnel: Specifications • Primary Use: • The facility is used primarily for high Reynolds number testing, including the development of high-lift systems for commercial transports and military aircraft, high angle-of-attack testing of maneuvering aircraft, and high Reynolds number research. • Capability: • Mach Number: 0-0.52 • Reynolds Number per foot: 0.1 - 12X106 • Stagnation Pressure, PSIA: 2.0 - 90 • Temperature Range: 540 ° - 610 ° R • Closed circuit, single return, variable density, closed throat, wind tunnel with exceptionally low turbulence • Model-support systems available: • Strut with variable pitch and roll capability • High angle-of-attack turntable system • Dual-strut turntable mechanism for high-lift testing • Semi span mounting system • Internal strain-gage balances used for force and moment testing • Capability for measuring multiple fluctuating pressures • Temperature-controlled auxiliary high-pressure (3000 psi)

  11. Wind Tunnel Power Requirements

  12. Energy Ratio Subscript 0 refers to the test section P is the motor power is the fan efficiency

  13. Wind Tunnel Circuit Elements

  14. Losses Local Pressure Loss Coefficient Pressure Loss Referred to Test Section Section Energy Loss

  15. Closed Return Tunnel

  16. Example - Closed Return Tunnel

  17. Example - Open Return Tunnel

  18. Turbulence Management System Stilling Section - Low speed and uniform flow Honeycomb - Reduces Large Swirl Component of Incoming Flow Screens - Reduce Turbulence [Reduces Eddy size for Faster Decay] - Used to obtain a uniform test section profile - Provide a flow resistance for more stable fan operation

  19. Test Section Test Section - Design criteria of Test Section Size and Speed Determine Rest of Tunnel Design Test Section Reynolds Number Larger JET - Lower Speed - Less Power - More Expensive Section Shape - Round-Elliptical, Square, Rectangular-Octagonal with flats for windows-mounting platforms Rectangular with filled corners Not usable but requires power For Aerodynamics Testing 7x10 Height/Width Ratio Test Section Length - L = (1 to 2)w

  20. Wind Tunnel Measurements • Pressure measurement • Pitot-static tube • Manometers • Pressure gauges • Pressure transducer • Velocity measurement • Pitot tube • Hot-wire anemometer • Forces & Moments • Three component balance • Six component balance

  21. Pressure Measurement Measurement of Static pressure

  22. Static pressure tube

  23. Static pressure tube for supersonic flow

  24. Total pressure tube

  25. Pitot static tube

  26. Manometers The difference in fluid height in a liquid column manometer is proportional to the pressure difference.

  27. Multi tube Manometer

  28. Pressure gauges Based on the principle of hooks law

  29. Pressure Transducer

  30. Strain gauge based

  31. Piezo-electric type

  32. Pressure Transducer

  33. Velocity Measurement

  34. Hot-wire anemometer

  35. Working principle • The principle of the hot-wire anemometer is based on the variation in the rate of cooling of electrically-heated wires, with the flow velocity of fluid streaming past them. • The rate of heat transfer from the heated wire to the particles of the moving fluid depends on the diameter and composition of the wire and the physical characteristics of the flowing medium. • Since the electrical resistance of the wire depends on its temperature, a simple electrical-resistance measurement can be used to determine the velocity. • The dependence of the anemometer resistance on the velocity is determined by calibration in a wind-tunnel against a reference instrument.

  36. The main characteristic of the hot-wire anemometer, namely its high sensitivity at low flow velocities. • At constant resistance the current changes with velocity most rapidly at small free-stream velocities. • Sensitivity increases with the wire temperature throughout the velocity range. • The temperature of the wire is, however, limited by aging and strength considerations and should not exceed 400 to 500°C. • If the current through the wire is held constant, the changes in temperature and resistance of the wire can be predicted. • Hot-wire anemometers may therefore be used to measure velocity either at constant resistance or at constant current. • For measurements at constant resistance the wire forms one arm of a Wheatstone bridge, the other arms being resistors • having a negligible temperature coefficient.

  37. A change in the velocity causes the temperature and resistance of the wire to change; this unbalances the bridge. • In order to restore the balance of the bridge the wire temperature is restored to its initial value by adjusting the resistance of the adjacent arm or of an auxiliary resistor. • Velocity is measured in terms of the current in the wire, as indicated, for instance, by an ammeter connected in an external circuit.

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