Water fog generation system for subsonic flow visualization

The obvious need for a unique system which would be clean, nontoxic, noncorrosive, nonflammable, and chemically inert in normal usage has led to the development of a liquid nitrogen-steam fog generating system for subsonic flow visualization in a wind tunnel. Attention is focused on a description of the designed experimental apparatus and on the operation experience with a prototype system. The fog generator is basically a very simple device which allows steam and liquid nitrogen to be combined turbulently in a mixing nozzle and then expelled. The prototype mixing nozzle is mounted outside of the wind tunnel, and the fog is piped to the inlet of the contraction section of the tunnel with 1-inch inside diameter plastic tubing. The optical appearance of the fog is almost as opaque as titanium tetrachloride smoke and is comparable to oil or tobacco smoke. The designed prototype is capable of producing optically dense water fog in a subsonic wind tunnel. The technique appears well suited for wind-tunnel flow vizualization of all types. Points to be stressed in building a fog system are noted.