In the study of supersonic flow, shock and expansion waves are used to determine Mach number. In most situations, however, they are virtually invisible to the naked eye. Fortunately, a system developed in 1864 by German Physicist August Toepler allows waves to be viewed clearly for accurate angular measurements.
Schlieren (plural for the German word “schliere”) are optical inhomogeneities in transparent materials. In supersonic flow, air experiences very large changes in density as it approaches, passes through and trails shock waves. As the density of air changes, so does its index of refraction. Changes in index of refraction essentially turn the shock waves into lenses, bending the light. Toepler’s Schlieren “system” separates the light bent by the shock waves from the background light, allowing the shocks to be viewed as a combination of bright and dark areas.
Individually crafted, AEROLAB offers Schlieren Systems for any application: supersonic wind tunnels, transonic wind tunnels, supersonic nozzle study, etc.