Turbulent Entrainment in Buoyant Jets and Plumes

The behavior of turbulent buoyant jets in uniform density environments is found to be governed by an entrainment function and buoyancy function, both of which are functions of the local jet densimetric Froude number and the local jet spreading angle. For plumes, Batchelor’s analysis is used to show that the local Froude number and jet angle are constant. These two facts are then used to show that the buoyancy and entrainment functions in plumes are also constant and that their values can be deduced from an experimental velocity profile alone. Experimental results are also used to show that the axisymmetric buoyant jet is virtually independent of elevation and this result leads to the conclusion that the entrainment function is linearly dependent on the inverse of the local jet Froude number, thus confirming the result obtained by Priestly and Ball (1955). The buoyancy function is found to be constant with the value 1.16 for axisymmetric buoyant jets.