A method of analyzing the mixing characteristics of binary liquid jets in a liquid stream has been developed. It consists of a modified schlieren system in which the aperture of the camera lens acts as a circular schlieren knife edge. The liquid stream which is to be studied is placed in the schlieren field. This liquid stream is in a glass tube which is contained in a rectangular glass-sided cell filled with liquid of about the same index of refraction as the glass tube. This masks the refractive effect of the glass tube and much of the lens effect of the round cross section of the stream. It is shown that for a definite minimum energy of injection, the mixing becomes essentially complete at the end of the mixing region. The region of mixing appears on the photographs as a region of special turbulence above the jet openings in which the jet energy is being dissipated.
GEORGE G. KRETSCHMAR and HENRY W. WEDAA, "An Optical Method for the Study of Impinging Jets in a Liquid Stream," J. Opt. Soc. Am. 43, 526-528 (1953)