Negatively buoyant fluid projectiles

Ole Joergen Myrtroeen, Gary Hunt, Imperial College Urban Cities Programme
2012
An experimental study concerning the rise height and morphology of a negatively buoyant fluid projectile, produced when a finite volume of saline solution is forced vertically upwards into a quiescent and uniform fresh water environment, is presented. Unlike the much studied continuous injection of high Reynolds number negatively buoyant fluid giving rise to a turbulent fountain, the behaviour of a finite volume negatively buoyant release remains, until now, unstudied. The work presented herein
more » ... is based on the development of an experimental set up and methodology specifically tailored to the study of the negatively buoyant projectile. We commence by identifying the two source parameters governing the behaviour of the negatively buoyant projectile; namely the source Froude number FrD, expressing the ratio of source momentum to source buoyancy, and the aspect ratio of release L/D. relating the length L of the column of saline solution dispensed to the nozzle diameter D. In doing so, we note the link to turbulent fountains (continuous negatively buoyant releases) whose behaviour is governed solely by FrD and to vortex rings (finite volume neutrally buoyant releases), whose behaviour is governed solely by L/D. Based on its differing rise height behaviour and morphology of release (for varying FrD and L/D), we classified the negatively buoyant projectile into one of three regimes: the weak-fountain regime, where the rise height behaviour of the negatively buoyant projectile adhered to very weak fountain predictions; the vorticity-development regime, where the development of an internal vortical structure within the head of the negatively buoyant projectile inhibited its vertical propagation; and the forced-release regime, where the rise height behaviour of the negatively buoyant release adhered, under certain source conditions, to forced fountain predictions. This adherence of the rise height behaviour of negatively buoyant projectiles to fountain rise height predictions led to a study of the source conditions (in ter [...]
doi:10.25560/9212 fatcat:mdpmevzwevdv5jjni3bchldcmm