DECAYING 2-DIMENSIONAL TURBULENCE WITH RIGID WALLS

Decaying two-dimensional Navier-Stokes turbulence (or turbulence for t he corresponding electrostatic ''guiding center'' plasma) has usually been studied in spatially periodic boundary conditions. It is known to exhibit a variety of features which are different from the three-dime nsional case. By means of spectral-method direct numerical computation , we show that circular no-slip boundaries can significantly alter the decay scenario in two dimensions. In particular, the wall functions a s an important source of vorticity and vorticity gradient, and the dec ay of energy is enhanced by this effect, relative to the decay in peri odic boundary conditions. In addition, the very slow decay of angular momentum in high Reynolds number cases constrains the evolution in a w ay that has no analogue for rectangular periodic boundary conditions.