Professor GertJan van Heijst,
Eindhoven University of Technology, The Netherlands,
will give the lecture
"The behavior of vortex structures near solid obstacles"
Abstract:
Two-dimensional turbulence is characterized by the inverse energy cascade, which results in self-organisation of the flow, as seen in the emergence of coherent vortex structures. These coherent flow structures may take the form of monopolar or dipolar vortices, and even a tripolar vortex has been found. The lecture will provide an overview of the basic dynamical features of two-dimensional turbulence, and in particular highlight the role of solid boundaries on the flow evolution.
A special point of attention is the behaviour of vortex structures near solid obstacles in the flow domain. We will address the problem of a dipolar vortex approaching solid objects like a cylinder, a row of closely positioned cylinders, or a sharp-edged plate. Vorticity generated at the no-slip surface of the obstacle or due to flow separation at sharp edges is advected away from the wall and may thus interact with the primary vortex structure. This may lead to very complicated behaviour, like splitting and partial rebound of the primary dipole.
Laboratory experiments have been performed in a rotating fluid tank, the background rotation providing a mechanism for making the relative flow approximately two-dimensional. The flow evolution has been visualized by adding dye, while quantitative information about the vorticity distribution was obtained by PIV measurements. In addition to numerical flow simulations, some analytical studies have been carried out, which provide important information about the vortex-wall interaction.