Observations of the surface thermal signature of buoyant plumes: Impacts of temperature anomaly, flow rate, and polymers

Surface thermal signatures of a buoyancy-induced flow can reveal the evolving organization of flow structures, allowing for an understanding of their role in entrainment/mixing processes. This is of utility when the flow is still transient, where its mathematical description does not follow conventional similarity variables and power-law scaling. One such aspect of a thermal buoyancy-induced transitory flow is the surfacing of ambient cold-water pockets, captured and analyzed in our experiments. To further elucidate the causality of these pockets with regards to the turbulent nature of the subsurface flow, they are analyzed with and without turbulence-inhibiting polymer additives. Consequently, these pockets are objectively identified as coherent flow-features via proper orthogonal decomposition mode analysis. Resulting modes and their rank distribution are presented. Pocket correlation length scales are then analyzed with varying volumetric flow rates and temperature difference between the ambient and the plume source. For the polymeric cases, the additional parameter of Weissenberg number is included to draw upon the influence of turbulent flow on the evolution/formation of these pockets. Differences between the polymeric and non-polymeric cases are then interpreted to attempt a scaling for the evolution of such pockets and shed light on their formation mechanics via the entrainment process.