Characterizing visual structures in a buoyant plume

Turbulent plumes are fascinating to study in large part due to the ability to see the eddies and structures that comprise the exterior structure as they develop in space and time. We perform a laboratory study in which positively buoyant turbulent plumes are generated in a quiescent water tank. Buoyancy is varied by modifying the relative percentages of isopropyl alcohol to water in a mixture placed in a head tank. Photographs captured at steady frame rates record the evolution of the plume as it develops in time and space. A custom algorithm tracks the visible exterior outline of the plume, from which eddies and structures can be identified along the interface between the plume fluid and ambient fluid. Statistical analyses are performed to characterize differences in the distributions of external structures to study their dependence on relative buoyancy between the fluids. Spectral analysis of the edge signal of the plume reveals a \(-\)2.2 slope, indicative of the range of eddy lengths that comprise turbulent plumes. We explore the relationship between buoyancy with both the plume front velocity and plume spread angle. We find the front velocities to be functions of both the buoyancy and source Reynolds number. However, the spread angles were found to vary only with buoyancy of the plumes, thus proportional to their Richardson numbers.