The formation of coherent structures within turbulent fountains in stratified media

An experimental investigation into the interaction between a turbulent fountain and its stratified environment is presented. A heavy fluid, cold water, is injected vertically upwards into a linearly stratified medium. As revealed by visualisations, the heavy-fluid jet reaches a maximum height before it begins to fall under to the effect of gravity. Due to fluid mixing and entrainment, the vertical momentum and the density of the jet fluid decrease as it submerges to an intermediate height of zero buoyancy. Large coherent structures are identified using Proper Orthogonal Decomposition (POD) on Digital Particle Image Velocimetry (DPIV) measurements. Experimental values of the main components of temporal and spatial spectra are compared to predictions based upon the dispersion relations for stratified media.