Aerospace Engineering Iowa State University 311L Schlieren & Shadowgraph Methods Aerospace Engineering 311L

Aerospace Engineering Iowa State University 311L Models of Light m/s Physical (wave) model Wave Peaks Geometric model Light Rays

Aerospace Engineering Iowa State University 311L Light From a Point Source

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 Air Water1.33 Crown glass1.52 Plexiglas1.51 Diamond2.42 For gases: = gas density k = 0.23 cm 3 /g for air

Aerospace Engineering Iowa State University 311L Light Refraction Medium 2 Medium 1 Snell’s Law:

Aerospace Engineering Iowa State University 311L Example, Refraction in Water Water Surface Pole

Aerospace Engineering Iowa State University 311L Lenses Focus

Aerospace Engineering Iowa State University 311L Lenses Point Source

Aerospace Engineering Iowa State University 311L Direct Shadowgraphy Point Source Bubble of high density gas

Aerospace Engineering Iowa State University 311L Shadowgraph Image

Aerospace Engineering Iowa State University 311L Some Math x y z or

Aerospace Engineering Iowa State University 311L The Basic Schlieren System Point Source

Aerospace Engineering Iowa State University 311L The Real Schlieren System Extended Source

Aerospace Engineering Iowa State University 311L Schlieren Image

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

Aerospace Engineering Iowa State University 311L Mirrors

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

Aerospace Engineering Iowa State University 311L Light Source Lamp Condenser Lens Section A-A A-A

Aerospace Engineering Iowa State University 311L Setting Up The Schlieren System Step 1: Find the focal length of the field mirrors Focal Length

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

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

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

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

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

Aerospace Engineering Iowa State University 311L References G.S. Settles, Schlieren & Shadowgraph Techniques, Springer-Verlag, D.C. Giancoli, Physics for Scientists & Engineers, Prentice Hall, 1988.