The use of an improved diffraction grating interferometer.

A conventional schlieren system was converted into a Kraushaar interferometer by the addition of matched diffraction gratings as the beam splitting and recombination elements. Optical quality of the added features of this installation were shown to be not a limiting factor, but the optical platform must be isolated well for good results. Basic optical theory applicable to this device is summarized. Several aspects are indicated which enhance the fringe or image quality. This device has been used to find the surface pressures and flow field structure around some simple two-dimensional airfoil shapes. Comparison of these results with calculations indicates good agreement between the diffraction grating interferometer data and analytical data.