This issue collects together a series of papers representing a cross-section of the research presented at the 2nd International Conference on High-Reynolds Number Vortex Interactions, held in Brest, France from 31 August until 2 September 2009. This conference was attended by more than 50 participants from around the world, and 35 talks were presented. It was organised jointly with the Laboratoire de Physique des Océans, Université de Bretagne Occidentale in Brest and the University of St Andrews in Scotland. The 1st conference was held in Toulouse in August, 2005.
The conference primarily addressed topics in geophysical fluid dynamics, but a few talks covered more general topics such as stratified turbulence, chaotic motions of confined flows, aerodynamics, and magnetohydrodynamics. A wide range of approaches were taken, ranging from experimental, numerical to theoretical analyses. The purpose of the conference was to bring together researchers studying vortex dynamics in order to share ideas and methods, and to thereby stimulate further collaboration.
Vortex interactions are highly nonlinear features of fluid flow at very high Reynolds numbers. Indeed, the most complex state of fluid motion – turbulence – can be meaningfully thought of as competing vortex interactions occurring across a wide range of spatial and temporal scales. Understanding vortex interactions, thus, may help better understand the fundamental, physical nature of turbulence. Fluid flows, however, come in many forms depending on the context. In geophysical flows, the effects of rotation and stratification are paramount, at least at intermediate to large scales. Stratification continues to play an important role down to much smaller scales (less than a kilometre in the atmosphere). As a result, vortex interactions in geophysical flows depend critically on these external effects, and many others such as topography, forcing, damping, boundaries, etc. In short, the parameter space is exceedingly rich. Yet, the practical, urgent need to better understand our environment has brought forth a strong, multi-faceted, international research effort to quantify the impact of vortex interactions. The papers presented in this issue, while only a small sample of this effort, give a flavour of the various directions and topics currently being pursued, and reveal important new discoveries.