A rotating cylinder in an infinite fluid generates a stable rotational flow, but if the cylinder is suddenly halted, then an unstable flow is induced. Paul Cardinaels has kindly provided the Gerris simulation data for such a flow illustrating the vortex generation and shedding.

The original GFS file is converted to the more convenient GMT grd format and the resulting files are used to generate the arrows layer with:

vfplot \
    --verbose \
    --width 8in \
    --margin 5/5/-0.4 \
    --scale 1e-4 \
    --iterations 300/5 \
    --pen 0.1mm \
    --fill 100 \
    --length 0/1in \
    --cache 256 \
    --aspect 3.0 \
    --symbol triangle \
    --output vfplot.eps \
    grd/u.grd grd/v.grd

The arrows layer is then composited using GMT, a grd file of vorticity and a colour scale derived from the diverging Andy GIlmore 2 scheme.

Download the plot as pdf or inspect the GitLab sources.