Design and Performance of a Simple Interferometer for Wind Tunnel Measurements

The design of an interferometer with a 3 1/2" diameter light field and its application to a continuously operating 4" x 10" supersonic wind tunnel are discussed. The main features of this interferometer are (1) its very law cost compared to previous designs, (2) its light weight and flexibility, (3) a simple device permitting the instrument to be used also as a Schlieren system, and (4) its unique feature of passing both light beams through the test section to minimize the effect of the side wall boundary layers in the interferograms