Some recent experimental results concerning turbulent Coanda wall jets

Abstract

The Coanda effect is the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. As a result, in such jets mixing takes place between the jet and the ambient air as soon as the jet issues from its exit nozzle, causing air to be entrained. This air-jet mixture adheres to the nearby surface. Whilst devices employing the Coanda effect usually offer substantial flow deflection, and enhanced turbulence levels and entrainment compared with conventional jet flows, these prospective advantages are often accompanied by significant disadvantages including a considerable increase in associated noise levels and jet breakaway. Generally, the reasons for these issues are not well understood and thus the full potential offered by the Coanda effect is yet to be realized. In this paper, the results of recent modelling and experiments on a 3-D turbulent Coanda wall jet are presented. The potential application of these results to important problems of practical interest such as launch noise is also discussed, and recent data pertaining to rocket launch noise sources is presented.