Compressible Fluids: the discontinuity of the vorticity vector on a   shock wave in thermodynamical variables
  The discontinuity of the vorticity is written as a function of the vector T grad s, (where T is the temperature and s the specific entropy). The expression is obtained thanks to potential equations and independently of the mass conservation and the equation of momentum balance. 
Henri Gouin (MSNMGP, LMMT)