Time similarity analysis of unsteady buoyant plumes in neutral surroundings

Abstract

A time similarity formulation of the flow equations for unsteady plumes is shown to exist only when the buoyancy flux at the source varies as a power function of time. The time similarity equations for unsteady plumes are solved numerically. It is shown that the velocity of the leading edge of the plume is less (at most the 0·42 fraction) than the velocity inside the plume behind its leading edge; this observation is consistent with Turner's (1962) results on the behaviour of a starting plume with constant buoyancy flux at the source. Finally, experimental results of axial temperature histories in the buoyant plume generated by a fast-growing fire are compared with the theoretical predictions.