Hysteresis of the Coanda Effect

For scientist, the Coanda effect has been an object of interest for a long time. All the time, some new applications of it are found although it has been more than a hundred years since Henri Coanda got a patent that was critical for that issue. Apart from aviation, it is more and more often used in ventilation systems to control the manner of air division and the design nozzles and ventilators. It is surprising, however, that a good command of that phenomenon and a need to apply it in different solutions did not entail a significant increase of the interest in the Coanda effect hysteresis, although it was mentioned for the first time by Newman in 1961. This article presents results of experimental measurements for a two-dimensional incompressible plane jet by an inclined plate. The hysteresis has been observed as a different jet behavior (a free jet or a jet attached to a flat plate) depending on the direction in which the plate deflection angle changes. The observed hysteresis area, defined by critical values for the α_ca attachment and α_cd detachment angles, spanned from 8 deg to 14 deg. Its dependency on the Reynolds number has also been examined for Re ranging from 3500 to 26,500. Considering the Coanda effect hysteresis, a pressure distribution on the plate and the x_R reattachment distance has been examined. The distribution of forces on a plate has been identified, which has facilitated a graphical mirroring of the Coanda effect hysteresis loop.