## Two-dimensional turbulence on a bounded domain—the role
of angular momentum

*GertJan F. van Heijst*, Fluid Dynamics Laboratory, Dept
of Physics, Eindhoven University of Technology

In contrast to its counterpart in the 3D world, turbulence in
2D is characterized by an inverse energy cascade. The presence of
this inverse cascade in 2D turbulence is visible in the so-called
self-organization of such flows: larger vortices and structures
are observed to emerge from initially random flow fields.

The lecture will address the evolution of 2D turbulent flows on
a finite domain with no-slip walls. The organized state consists
of a large, domain-filling cell whose motion can be considered as
inviscid and hence governed by the Euler equation. Results of both
laboratory experiments in rotating/stratified fluids and
numerical simulations, however, reveal the crucial role played by
the unsteady boundary layers: the domain boundaries act as
important sources of large-amplitude vorticity filaments that may
influence the motion in the interior. Attention will be given to
global flow quantities like the kinetic energy, the enstrophy, and
the total angular momentum. In the case of forced 2D turbulence,
the latter quantity may show a remarkable flip-flopping behaviour,
associated with a collapse of the organized flow state followed by
its re-organisation.