  A spherical hydrodynamical expansion flow can be described as the gradient of
a potential. In that case no vorticity should be produced, but several
additional mechanisms can drive its production. Here we analyze the effects of
baroclinicity, rotation and shear in the case of a viscous fluid. Those flows
resemble what happens in the interstellar medium. In fact in this astrophysical
environment supernovae explosion are the dominant flows and, in a first
approximation, they can be seen as spherical. One of the main difference is
that in our numerical study we examine only weakly supersonic flows, while
supernovae explosions are strongly supersonic.
