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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 generally 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. The development of a model for predicting the noise emitted by three-dimensional flows over Coanda surfaces would suggest ways in which this noise could be reduced or attenuated. In this paper, the results of recent modelling and experiments on a 3-D turbulent Coanda wall jet are presented. They include the relationship of SPL, shock cell distribution and breakaway to various flow parameters, and predictions of the jet boundary. 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.

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The following article appeared in Proceedings of Meetings on Acoustics (Vol. 22, No. 1, p. 040004) and may be found at