Free-surface effects on spin-up in a rectangular tank

The dependence of spin-up in a rectangular tank: on deformation of the free surface is investigated experimentally. The results agree with earlier experimental and numerical data about the motion of vortices over topography. However, the presence of sidewalls appears to interact with the vortex drift induced by the surface topography. This combined effect provides a qualitative explanation for the observed behaviour of individual vortices. In particular, in the presence of free-surface deformation, cyclonic vortices in an elongated rectangle tend to drift away from the centre of the tank, so that their merging in the centre is discouraged.