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Aerodynamic Testing

Aerodynamic Testing. Chapter 9. History of Wind Tunnels. 1st attempts at performing aerodynamic testing was Sir George Cayley. Langley also used also used a device to aid in the development of his aerodromes. Da Vinci the basics of wind tunnel (fixed position, force air to flow over it).

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Aerodynamic Testing

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  1. Aerodynamic Testing Chapter 9

  2. History of Wind Tunnels • 1st attempts at performing aerodynamic testing was Sir George Cayley. • Langley also used also used a device to aid in the development of his aerodromes. • Da Vinci the basics of wind tunnel (fixed position, force air to flow over it)

  3. First Wind Tunnels • 1st wind tunnel recorded in history was developed by Francis Wenham of England. • Simple box with air blown through by a fan • The 1st American wind tunnel was built at Massachusetts Institute of Technology in 1896. • The largest in the world was built in Ames Research Center in California with a test section of 40x80

  4. Wind Tunnel Design • Open-circuit or Straight through type. • Wright Brother’s tunnel • simple & very efficient • figure 9-2, 9-5, 9-6 • small open-circuit tunnels are usually inside a building • large tunnels must be open to outside are susceptible to dust ect. • Open-circuit tunnels are very noisy & surrounded by high wind current

  5. Wind Tunnel Design • Closed-Circuit or Return Type • Air is accelerated by the fan and flows through the tunnel • Turning vanes are installed to guide flow around the corner • The tunnel widens into a large settling chamber to decelerate the air; preventing a large build up of large boundary layer along the wall

  6. Wind Tunnel Design • Single-Return Type • all wind tunnels discussed thus far have been single-return • Double Return Type • divides the flow downstream of the test section and runs through two circuits, each with a driving fan. • The flow then joins as it enters the settling chamber & proceeds through a single test section

  7. Wind Tunnel Design • Annular • An extension of the double-return concept • A return passage is located around the entire circumference of the wind tunnel outside the test section • This design was employed in the NACA variable density tunnel • figure 9-3

  8. Wind Tunnel Design • Spin Tunnel • Special type of annular tunnel employed at Langley Research Center for spin research. • Is mounted vertically with the fan drawing air upward • Models are introduced into free-flight conditions then vertical flow adjusted • Figure 9-9

  9. Types of Wind Tunnel Tests • Original testing in wind tunnels was to a provide a means to determine lift & drag on airfoil shapes. • Force Test • Force measurement requires a force to be exerted (lift & drag forces so termed force test) • The balance can measure only two forces: lift & drag

  10. Six-Component Balance • A more complete balance that can measure all six measures & moments about all three axes of the airplane • Figure 9-10 p. 256 • Six component wind tunnel balance • this balance measures forces by use of strain gauges

  11. Types of Wind Tunnel Tests • Pressure Tests • Insert tiny tubes into the model surface or airstream and connect them to a pressure measuring device • Liquid Manometer-pressure measuring device • Figure 9-11 p. 258 • Tiny hole (pressure taps) drilled into the top of the surface, series of tubes, water added & measured

  12. Types of Wind Tunnel Tests • Figure 9-12 • Lowered pressure over the wing surface reduced the pressure in the manometer tubes and draws the water level up to a high level • The lower the pressure, the higher the water level goes • Measuring the difference in water level will show the relative pressure difference

  13. Types of Wind Tunnel Tests • Flow Patterns • Allow the streamlines of air flow to look at the body’s aerodynamic properties • Tufting allows for the flow pattern visualization • Tufting –the attachment of small tufts of yarn to the surface • The tufts will show if flow is attached or separated to form a wake • Figure 9-14 p. 260

  14. Types of Wind Tunnel Tests • Flow pattern • visualized by the use of smoke at the Embry-Riddle smoke tunnel • Figure 9-15 p. 261 • Smoke is generated by burning oil; then injected into into the airstream • Oil flow techniques can also be used to study flow patterns

  15. High Speed Wind Tunnels • Supersonic tunnels-1st developed in Germany, Busemann who also developed the swept-wing concept • Early supersonic tunnels were the blow down type at Mach 1 • One of the most difficult conditions to create the flow at exactly Mach 1 • Figure 9-16, 9-17 p. 262-263

  16. Shock Wave Visualization • Shock Waves are made visible by light refraction called the Schlieren method (ch7) • Figure 9-19 p. 265 • Figure 7-3 p. 192 Schlieren photograph

  17. Wind Tunnel Testing Problems • Wall Effect • Walls are artificial boundaries that airplanes do not have • Upwash/downwash from walls, floors, ceiling • Scale Effect • Small models have small forces making measurements inaccurate • Differences in Reynolds number between model and the full-scale model

  18. Flight Testing • Shakedown Tests • Basic flight qualities are determined • Airplane’s Performance • An exact determination of top speed, cruise speed, range, rate of climb, takeoff & landing distance • Stability & Controllability • Exact degree of stability, handling qualities

  19. Flight Testing • Performance • Special instruments take measurements in test flights • Figure 9-22, 9-23 p. 270 • Pressure Measurements • Attaching pressure measuring devices to taps on the aircraft surface • Figure 9-20 p. 268 • Flow visualization • Tufts similar to wind tunnel testing • Reveal poor aerodynamic characteristics • Figure 9-21 p. 269

  20. Quiz on Chapter 9 Please take out a sheet of paper Include today’s date and your name

  21. Quiz on Chapter 9 • Compare and contrast wind tunnel testing and flight testing.

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