1. Tracer problem

There are three aspects to the tracer problem.

A tracer is a foreign body present in the fluid to be analyzed; it may sometimes be naturally present (dust or condensation mist in air, bubbles in water), but is most often introduced artificially by the experimenter. The seeding operation must therefore be non-disturbing if the non-intrusive nature of the visualization is to be preserved. The principle adopted must therefore comply with strict rules: the obstacle constituted by an injector must not introduce parasitic phenomena; injection speed and temperature must be close to those of the flow; the number of tracers must be limited so as not to modify the physical...