A study of round, line-like and meandering turbulent fountains

Abstract

The dynamics of different classes of turbulent and miscible fountains are stud- ied: from classic axisymmetric fountains issuing from round sources, to confined fountains propagating in a quasi-two-dimensional environment, to line fountains which form when release conditions are approximately two-dimensional at the source. Each class is characterised by distinct dynamical behaviour, which this the- sis analyses both through theoretical arguments and experimental measurements. A model for the entrainment of ambient fluid into a fluctuating fountain top is developed and implemented into a first complete description for round fountains. The solutions of the resulting ‘three-region-model’ lie in improved agreement with available data and, uniquely, do not diverge near the top of the fountain. Next, con- fined fountains (unexplored to date) are classified into four flow regimes and their behaviour collapsed according to a single governing parameter that captures the severity of confinement. Finally, new experiments on line foutains shed light on the quasi-steady structure of these flows, revealing (and motivating) a strong con- nection between their motion in the vertical and lateral planes. Round, confined and line fountains are then contrasted in the conclusions, where we reflect on what is required to progress towards a unified theory of turbulent fountains.