Visual structures in laboratory generated buoyant plumes*

Turbulent plumes are comprised of eddies and cauliform structures that visually highlight their dynamic nature as they develop in space and time. We present a series of laboratory experiments from which we analyze the visual signatures of turbulent buoyant plumes. We explore three different buoyancy conditions by mixing isopropyl alcohol into water released through a pipe at the base of a water tank, exploring Richardson numbers ranging from 1.4 to 2.0. By dyeing the plume mixture with fluorescein salt, with illumination provided by black lights, the plume exterior is visible for optical tracking. We capture the development of the starting plumes using continuous series of photographs collected at steady frame rates. A custom algorithm tracks the outline of the plume exterior, from which eddies and flow structures can be identified. We find the distribution of structure sizes follows a lognormal distribution. We find the plume spread angle to vary with initial buoyancy, and the front velocity to vary with buoyancy and Reynolds number. We perform spectral analysis on the edge signal of the plume from which we measure a slope of -2.2. We also explore the transition to turbulence as the plume begins to develop, with an interest in characterizing entrainment mechanisms and the dynamics of the interface between the turbulent plume fluid and quiescent ambient fluid.