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Show -15- field, viz. the evaporation of the water content of the slurry. On the basis of these arguments the near field aerodynamics programme was commenced in 1983. In the preliminary phase (NFA0), a background study [ 16 ] in which existing experimental data and similarity parameters which have been used to predict phenomena in swirling flows, were reviewed. It was concluded -that certain aspects of swirling flows particularly recirculated mass flow rates in the internal recirculation zone and mixing intensities between different flow regions are not very well understood. This inability to predict swirling flow phenomena is partially attributal to a lack of understanding about what physical forces give rise to the special and sometimes remarkable characteristics exhibited by swirling flows. A review of analytic solutions to the equations of motion for swirling flows in some special geometries have shown that they can give invaluable insight into the physics of these type of flows. In particular the ability of swirling flows to support upstream wave propagation of inertial waves above a certain critical swirl number implies that swirling flows can be split into two categories; supercritical flows and subcritical flows. Supercritical flows cannot support upstream inertial wave propagation, while in subcritical flows these special types of wave forms may propagate upstream and transmit information concerning downstream conditions. Following from this, an experimental programme was proposed which was based on assessing the validity and usefulness of the appropriate analytical solutions to the equations of motion available, in geometries and with velocities which simulate industrial swirl burner conditions, and to extend the analytical solutions where it is necessary with empirical corrections. Thus far the experiments planned (NFAl and NFA2) were to be executed in a cold model. The final phase of the programme (NFA3) will consist of real burner tests in order to incorporate the effect of combustion into a model of the |