Connecting surface thermal features with subsurface buoyant plume dynamics

Surface thermal signatures of a buoyancy-induced flow can be instrumental in investigating the evolution of subsurface flow structures, potentially allowing for remote sensing to replace in situ measurements. To study this, experiments were conducted using a vertically oriented plume in a tank (measuring 0.63m to a side) with a vertically mounted infrared camera imaging the free-surface. To this end, correlation length scale analysis at the free surface were conducted for a range of flow conditions to see how it varies with the Reynolds number defined by the source outlet variables. Furthermore, we analyze these trends by computing the power spectral density of the temperature fluctuations at the free surface. During this analysis, we also compare our results with the available literature, including similar experiments for a narrower range of Reynolds number by Judd et al. (2016, J. Visualization). To elucidate the role that the turbulent state of flow plays in the downstream evolution of the flow structures, and therefore the surface features, experiments are also conducted using turbulence-inhibiting polymers. Results are then analyzed and compared by including the Weissenberg number to the parameter space to draw upon the evolution of these structures, and thus the mechanics of the entrainment process. The need for appropriately defining the parameters quantifying the flow is also stressed in terms of the scale-separation concept underlying turbulent flows.