Three-dimensional measurements of an inclined vortex ring interacting with a density stratification

Vortex rings are generated every time an impulsive jet occurs in an ambient homogeneous fluid, for instance in thermal or density plumes in environmental applications. Those vortical structures, often referenced as building blocks of turbulence, exist in a wide range of scales. The velocity field associated with these toroidal vortical structures makes them self-propagating. Such vortices are likely to carry mass and momentum along their path and are therefore good candidates for driving mixing to locations that are remote from where the ring is created. In numerous environmental applications, vortex rings interact with a density stratification due to variations of salinity and/or temperature. The path followed by a light homogeneous and axisymmetric vortex ring impinging a layer of fluid stably stratified in density with a given angle. to the vertical, along with its dynamics and subsequent reorganization, are experimentally addressed in the present study. A three-dimensional time-resolved particle tracking velocimetry technique is set up to highlight the response of the stratified layer that is characterized by the generation of baroclinic vorticity and internal gravity waves. For the experimental parameters of the present study, the vorticity generation and reorganization, as well as the internal gravity waves in the stratified layer, are shown to remain axisymmetric for normal impacts. When the vortex ring propagation axis is not aligned with the density gradient, the expected symmetry breaking of the flow is observed. For inclined impact, the flow reorganizes in the form of a vertically flattened dipolar structure. In this case, internal gravity waves radiate away from two sources that match with the dipole cores.