Numerical Study of a Self-preserving Axisymmetric Turbulent Jet

Abstract

This paper examines computational modelling of a self-preserving axisymmetric turbulent jet, using a realizable second-moment closure with variable coefficients. The effect of omitting small second order terms in the equations of motion on the final result is investigated. To isolate the contributions of individual groups of small terms, four similarity solutions were obtained. The results show that omission of any of these terms is seen to affect the spreading and decay rates of the jet as well as the turbulent profiles. The combined effect of omitting all of the small terms is found to be relatively large near the axis of symmetry, in particular, in the profiles of the third moments. Now, since the gradients of third moments determine turbulent diffusion of turbulent kinetic energy, retaining these terms becomes a necessity for a more accurate prediction of the jet. Inclusion of all of the individual groups of small terms that hitherto had been omitted in thin shear-layer calculations produces significant improvement in the results in comparison with experimental data. Keywords: Jets, Turbulence modelling, Similarity solution