High Speed

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  1. Sources of Error
    • Human Error
    • Random Instrument Error
    • Systematic Error (from poorly calibrated equipment, difficult to read outputs, setup issue)
  2. Random Error
    Discrepancies between repeated measurements.  Also: Statistical/sampling error
  3. Accuracy vs Precision
    • Accuracy: Low Systematic Error
    • Precision: Low Random Error
  4. Shadowgraph: Why It Works
    • Changes in gas density change the index of refraction c0/c
    • light bends towards larger n, therefore light rays deflect towards regions of higher density
  5. Shadowgraph: Sensitive to?
    2nd Derivative of Density
  6. Shadowgraph setup
  7. Shadowgraph Ray Tracing
  8. Pressure Equation
    P_absolute=P_atm + P_Gauge
  9. Schlieren: Sensitive to?
    • First derivative of density
    • more sensitive than shadowgraph
  10. Common differences between schlieren and shadowgraph
  11. Schlieren setup (remember knife)
  12. Schlieren ray trace
  13. Horizontal Filter Characteristics
    • Vertical components of gradient visible
    • Downward Positive:Dark
    • Upward Positive:Light
  14. Why do we need supersonic airfoils? A traditional subsonic airfoil would...
    • Would generate a bow shock in front of the leading edge of the wing
    • Leads to an extreme increase in pressure directly upstream of the wing

    This results in significantly increased drag
  15. Temperature sensitive paint
    • Non Intrusive
    • luminescent molecule is excited by photons, emits a photon as electron returns to original energy level
    • Temperature can be found from the intensity
  16. TSP/PSP Pro Con
    Pros: Easy setup, non intrusive, high fidelity data, works for any size

    • Cons: Limited T range (-10 to 80ish)
    • Requires calibration
    • No Time resolved data
    • repaint models
  17. How to predict PSP/TSP
    PSP: Pressure up, collisional quenching increases, fluorescence decreases

    TSP:T up, thermal quenching up, fluorescence down
  18. Conduction
    Transfer of thermal energy via collisions or extension of bonds
  19. Convection
    Can only occur in fluids

    Whereas conduction results from the random motion ofatoms/molecules, convection results from bulk motion offluids
  20. Radiation
    Loss of thermal energy by the spontaneous emission ofphotons
  21. Why lasers?
    • Allow for non-intrusive measurement of all quantities of interest
    • Can be used to measure these quantities in highly luminous flows generallyinaccessible to other measurement techniques
  22. Laser Components
    • Excitation source (pump source)
    • Lasing medium (gain medium
    • Oscillator
  23. Mie Scattering
    • Flow is ‘seeded’ with very smallparticles
    • Particles are illuminated with a lasersheet
    • Can be time resolved
  24. Rayleigh Scattering
    Like Mie, but scattering off gas molecules or anotherseeded gaseous medium is imaged
  25. Raman Scattering
    • Incident light on moleculesexcites vibrational states tovirtual states rather than stableor metastable states
    • Run through spectroscope to determine composition
    • requires very thin linewidth lasers
  26. Laser Doppler Velocimetry
    • Flow is seeded with tracer particles
    • Overlapping beams focus at a very small interrogation volume

    • An optical detector measures intensity pattern at overlap location
    • relate intensity to V
  27. Particle Image Velocimetry
    • Particle Image Velocimetry (PIV)
    • Seed particles into flowfield

    A laser sheet is pulsed twice with a known time delay between pulses
Card Set:
High Speed
2016-12-13 03:34:31
High Speed aerodynamics

HS final
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