claw/applications/advection/2d/swirl

Swirling flow in a box

Edge velocities are stored in aux array (see setaux.f) with
velocity specified by differencing the streamfunction psi.f

The velocities are time-dependent giving reversing flow.  These
velocities are computed in b4step2.f.   The period is specified
by the parameter tperiod in setprob.data.   

In theory the solution should agree with the initial data at times 
t = N*tperiod/2 for all integers N, but because of the numerical 
diffusion this won't happen.

As a special case, if tperiod = 0, then 
the velocities are constant in time and b4step2 does nothing.
The velocities specified in setaux.f are then used at all times.

This test problem was used in:

@article{rjl:advect,
  author="R. J. LeVeque",
  title="High-resolution conservative algorithms for advection in
  incompressible flow",
  journal="SIAM J. Numer. Anal.",
  volume="33",
  year="1996",
  pages="627-665"
}