The optical methods for flow visualization in wind tunnels provide an interesting means of analysis. In order to extend their use, in transonic and supersonic flows, it is necessary to obtain photographs and high-speed pictures and a quantitative interpretation must be possible.
Two types of utilized equipment are described.
One of them is an interferometer of the horizontal Mach type. The other, called "interferential schlieren" apparatus, is the result of the application of the interferential contrast methods developed by Françon and Nomarski at the Institut d’Optique in Paris. In this paper, we describe two optical setups, the first for an over-all study of the flow over a model, the second for a detailed analysis of a small region.
Photographs obtained with these devices can be seen. They show how interesting is the interferential schlieren apparatus which permits, in certain cases, a quantitative analysis as precise as that provided by separated beams interferometry, but with a simpler equipment which is easier to handle, less sensitive to external vibrations, and less expensive.
R. CHEVALERIAS, Y. LATRON, and C. VERET, "Methods of Interferometry Applied to the Visualization of Flows in Wind Tunnels," J. Opt. Soc. Am. 47, 703-704 (1957)