The Fluxes and Behaviour of Plumes Inferred from Measurements of Coherent Structures within Images of the Bulk Flow

This paper describes how measurements of the movement of identifiable features at the edge of a turbulent plume can be interpreted to determine the properties of the mean flow and consequently, using plume theory, can be used to make estimates of the fluxes of volume (mass), momentum, and buoyancy in a plume. This means that video recordings of smoke rising from a chimney or buoyant material from a source on the sea bed can be used to make accurate estimates of the source conditions for the plume. At best we can estimate the volume flux and buoyancy flux to within about 5% and 15% of the actual values, respectively. Although this is restricted to the case of a plume rising in a stationary and unstratified environment, we show that the results may be of practical use in other more complex situations. In addition, we demonstrate that large-scale (turbulent) coherent structures at the plume edge form on a scale approximately 40% of the local (mean) plume half-width and travel at almost 60% of the average local (mean) velocity in the plume.The authors would like to acknowledge that the genesis of the work reported herein was a study investigating the physics of turbulent fountains, via coherent structure tracking, which was carried out by HCB and Prof. Gary R. Hunt (Burridge & Hunt, In Preparation). In addition, the authors gratefully acknowledge the skills and expertise provided by the technical staff at the G. K. Batchelor laboratory; HCB acknowledges the insightful comments of Prof. Colm-cille Caulfield. This work was supported, in part, by the Leverhulme Trust Research Programme Grant RP2013-SL-008, the EPSRC Programme Grant EP/K034529/1 and by the Royal Societ