Schlieren
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Schlieren are optical inhomogeneities in transparent media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such
Colored schlieren image of the thermal plume from a burning candle, disturbed by a breeze from the right
Schlieren flow visualization of a Lockheed SR-71 Pratt & Whitney J58 engine inlet at Mach 2
Shadowgraph
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Shadowgraph is an optical method that reveals non-uniformities in transparent media like air, water, or glass. It is related to, but simpler than, the schlieren and schlieren photography methods that
Schlieren
…Schlieren photography Shadowgraph Synthetic schlieren…
prehistoric shadowgraphy sunlight shadowgram of a martini glass "focused" shadowgram of a common firecracker explosion "Edgerton" shadowgram of the firing of an AK-47 assault rifle
Shadowgram of the turbulent plume of hot air rising from a home-barbecue gas grill.
"Edgerton" shadowgraph of bullet in flight
Shadowgram of shock waves from a supersonic bullet fired from a rifle. The shadowgraph optical technique reveals that the bullet is moving at a Mach number of about 1.9. Left- and right-running bow waves and tail waves stream back from the bullet, and its turbulent wake is also visible. To the right of the frame are seen unburned powder particles from the cartridge, themselves traveling slightly subsonic so that each of them produces a curved bow shock wave.