  We study the event-by-event generation of flow vorticity in RHIC Au + Au
collisions and LHC Pb + Pb collisions by using the HIJING model. Different
definitions of the vorticity field and velocity field are considered. A variety
of properties of the vorticity are explored, including the impact parameter
dependence, the collision energy dependence, the spatial distribution, the
event-by-event fluctuation of the magnitude and azimuthal direction, and the
time evolution. In addition, the spatial distribution of the flow helicity is
also studied.
