Influence of a Coflowing Ambient Stream on a Turbulent Axisymmetric Buoyant Jet

This paper reports numerical results on turbulent buoyant axisymmetric jets in a coflowing ambient stream. The objective of this study is to compare the performance of the Reynolds stress algebraic model (ASM) with that of the $k-ε$ turbulence model in predicting the flow field. A finite difference method has been used to solve a system of coupled partial differential equations. A comparison has been carried out between the numerical results obtained in the present work and experimental and numerical data reported in the literature. It has been found that the two investigated models reasonably predict the mean flow properties of the flow field. Nevertheless, the ASM proves to be better than the $k-ε$ method to predict the effects of buoyancy and the turbulence structure. It has been found that the increase of the coflow can slow the development of the jet to the state of similarity of mean characteristic profiles. A jet with a ratio of coflow velocity $u¯∞$ to jet discharge velocity $u¯0$ less than 0.05 has developed to closely approximate a free jet in a stagnant medium while a jet with higher $u¯∞∕u¯0$ ratio never reaches a similarity state. In buoyant jets, only a flow with $u∝∕u0⩽0.05$ reaches a similarity state. Buoyancy ensures that the similarity region begins at a distance closer to the nozzle exit than if the medium is stagnant.