Studies of Fluid Flow by Photography Using a Non-Disturbing Light-Sensitive Indicator

A powerful flow-visualization technique in described which overcomes the disadvantages of primitive flow-visualization methods (lack of precision, clarity and/or convenience relative to the commonly used probe techniques). The new technique uses a tracer fluid which is continuously present in latent form in the test fluid (eliminating injection problems) and which undergoes a dramatic color change (a reversible photochromic reaction) in a pattern generated instantly by irradiation with a pattern of ultraviolet light. A typical setup employs this fluid in some transparent flow channel, with an ultraviolet light source (such as a frequency-doubled ruby laser), a suitable background light source and a high speed motion-picture camera. Many previously intractable fluid dynamics problems have yielded to this technique, and improved resolution and the use of computer logging should greatly increase its utility.