Direct Measurement of the Density Field Using High Speed Differential Interferometry

The optical method presented here is based on Wollaston biprism differential interferometry using a white light source. It yields high-speed, instantaneous interferograms which directly display the isochoric lines of an instationary, two-dimensional flow. The setup is equivalent to conventional separate-reference interferometric systems, but remains differential since one of the beams — the one used as reference — lies inside the undisturbed upstream flow. The method was used to get instantaneous, high speed displays of the instationary flow around a cylinder placed across the test section.