Dimensional analysis has been used to derive formulae for dilution and trajectory for horizontal, buoyant, axisymmetric jets in still ambient, a coflow, a crossflow or a counterflow. The variation of the coefficients in the derived relationships are determined by analysing data obtained by the author and a number of other workers. The results have been presented in charts.

Further, a model to calculate the above flows which is based in the spreading concept has been outlined. The model is shown to describe simple cases well and is in these cases superior to models based on the entrainment hypothesis. However, work is still required to make the model cover the general case of a horizontal jet in an ambient flow.

A study has been made of the instability of jets in a counterflow. A number of behaviour modes are defined and described. On the basis of data from extensive experiments by the author a flow regime chart is presented which defines the occurrence of the different modes. The frequencies of one type of unstable, oscillating behaviour of jets in arounterflow are studied. A functional relationship between Strouhal number and the ratio between exit velocity and ambient velocity is found from dimensional analysis and experimental data.