Two-dimensional turbulence in square and circular domains with no-slip walls

Several fascinating phenomena observed for 2D turbulence in bounded domains are discussed. The first part of this paper concerns a short overview of the non-trivial behaviour of freely evolving 2D turbulence in square domains with no-slip boundaries. In particular, the Reynolds number dependence of, and the influence of the initial conditions on spontaneous spin-up of the flow, which is characterised by a sudden increase of the absolute value of the angular momentum of the flow, is investigated in more detail. In a second set-up we have investigated forced 2D turbulence in circular containers with no-slip walls. A comparison with the double periodic case reveals that domain-filling structures, always observed in the double periodic cases, are being prevented from emerging. Wall-generated, small-scale structures are continuously injected into the interior of the domain, destroying larger structures and maintaining the turbulent flow field.