The Prediction of the Axisymmetric Turbulent Jet Issuing into a Co-Flowing Stream

Abstract

SummaryThree analyses are presented for predicting the development of an axisymmetric turbulent jet issuing into a co-flowing external air stream. The first analysis is analogous to a method used by Patel to predict the growth of a two-dimensional jet in an external air stream. The method is found to be inadequate when the excess velocity on the axis of the jet becomes small compared with the external stream velocity. The second analysis assumes that the turbulence structure is similar at different streamwise stations but it breaks down when the advection of turbulent energy becomes comparable with the turbulent energy production. In the third approach, a two-parameter model of turbulence developed by Rodi and Spalding, which uses two differential equations for the turbulent energy and the length scale of the turbulence respectively, is found to predict closely the experimental results of Antonia and Bilger for a ratio of jet to external stream velocity of 3.0. The success of this last method emphasises the non-similar character of turbulence.