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Aerospace Engineering Iowa State University 311L Schlieren & Shadowgraph Methods Aerospace Engineering 311L
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Aerospace Engineering Iowa State University 311L Models of Light m/s Physical (wave) model Wave Peaks Geometric model Light Rays
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Aerospace Engineering Iowa State University 311L Light From a Point Source
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Aerospace Engineering Iowa State University 311L Speed of Light in a Medium Index of Refraction: c = speed of light in the medium Typical values: Mediumn = c o /c Air1.0003 Water1.33 Crown glass1.52 Plexiglas1.51 Diamond2.42 For gases: = gas density k = 0.23 cm 3 /g for air
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Aerospace Engineering Iowa State University 311L Light Refraction Medium 2 Medium 1 Snell’s Law:
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Aerospace Engineering Iowa State University 311L Example, Refraction in Water Water Surface Pole
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Aerospace Engineering Iowa State University 311L Lenses Focus
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Aerospace Engineering Iowa State University 311L Lenses Point Source
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Aerospace Engineering Iowa State University 311L Direct Shadowgraphy Point Source Bubble of high density gas
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Aerospace Engineering Iowa State University 311L Shadowgraph Image
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Aerospace Engineering Iowa State University 311L Some Math x y z or
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Aerospace Engineering Iowa State University 311L The Basic Schlieren System Point Source
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Aerospace Engineering Iowa State University 311L The Real Schlieren System Extended Source
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Aerospace Engineering Iowa State University 311L Schlieren Image
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Aerospace Engineering Iowa State University 311L Schlieren vs. Shadowgraph Displays a mere shadow Shows light ray displacement Illuminance level responds to No knife edge used Displays a focused image Shows ray refraction angle, Illuminance level responds to Knife edge used for cutoff Shadowgraph Schlieren
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Aerospace Engineering Iowa State University 311L Mirrors
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Aerospace Engineering Iowa State University 311L ISU’s Z-type Schlieren System 1 st Field Mirror 2 nd Field Mirror Screen/Instrument Panel Light Source Test Section Knife Edge
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Aerospace Engineering Iowa State University 311L Light Source Lamp Condenser Lens Section A-A A-A
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Aerospace Engineering Iowa State University 311L Setting Up The Schlieren System Step 1: Find the focal length of the field mirrors Focal Length
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Aerospace Engineering Iowa State University 311L Setting Up The Schlieren System Step 2: Set up the first field mirror 1 st Field Mirror Light Source Test Section
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Aerospace Engineering Iowa State University 311L Setting Up The Schlieren System Step 3: Set up the second field mirror 1 st Field Mirror Light Source Test Section 2 nd Field Mirror Screen/Instrument Panel
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Aerospace Engineering Iowa State University 311L Setting Up The Schlieren System Step 4: Set up the knife edge Focus the source image on the knife Adjust the cutoff Obtain a uniform darkening of the image
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Aerospace Engineering Iowa State University 311L Uniform Darkening Knife edge too close to second field mirror Knife edge too far from second field mirror Uniform darkening
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Aerospace Engineering Iowa State University 311L Some Notes The angle between the illuminator axis and the collimated beam should be kept to a minimum –Coma: Smearing of the mirror focus into a comet shape (cancelled out by tilting the mirrors in opposite directions, i.e. z-type system) –Astigmatism: Changes the focus into two short lines perpendicular to each other (limited by orienting the knife edge the same as the light source) A sheet of white paper is a good alignment tool A threaded bolt works well as a focusing tool
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Aerospace Engineering Iowa State University 311L References G.S. Settles, Schlieren & Shadowgraph Techniques, Springer-Verlag, 2001. D.C. Giancoli, Physics for Scientists & Engineers, Prentice Hall, 1988.
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