Wall roughness effect on Coanda fluid amplifiers

The effect of wall surface roughness on the operation of bounded jet flows and real fluid amplifiers is examined. The admissible or optimal roughness for real fluid amplifiers is defined and variations of surface roughness during fluid amplifier operation are studied. A large scale model is used to study the characteristics of jet flows between smooth and roughened parallel flat plates. The effect of roughness on the operation of real fluid amplifiers is measured using Coanda type fluidic elements of various make with artificially roughened cover plates. It is shown that roughness exceeding the admissible value influences the bounded jet flow not only by the increase of flow resistance but by the alteration of the whole flow structure.