The zone of flow establishment for plumes with significant buoyancy

The self-similar assumption used in jet and plume models is only valid for distances of greater than about six stack diameters downstream, in the zone of established flow (ZEF). The ‘Gaussian’ profile, observed at the beginning of the ZEF, must be related to source ‘top hat’ parameter values. However, previously used formulae are shown here to be approximations, being valid only for non-buoyant sources (‘pure jets’). Extensions to sources of significant buoyancy are described in terms of the densimetric Froude number, based on recently published experimental work.