Abstract
In this numerical study, several traditional scalar dissipation rate models are used for scalar transport modelling in mixing turbulent round jets with co-flowing air. These models are implemented into a second order turbulence closure model and are compared to the published experimental data. It is shown that the assumption of equal time scales for dynamic and scalar turbulence is no longer needed when the algebraic non-equal scales model or the transport equation model are used. The influence of these models on scalar mixture fraction, unmixedness, half-width of the jet and time scale ratio are examined. It is shown that the trends, which are observed in the experiments, are reproduced qualitatively by the non-equal scales model.