Vorticity and $\Lambda$ polarization in the microscopic transport model PACIAE.

We study the behavior of four types of vorticities in non-central Au+Au collisions at energies $\sqrt{S_{NN}}$ = 5--200 GeV using a microscopic transport model PACIAE. The results show that the vorticities decay faster at lower energy and smaller impact parameter. The non-monotonic dependence of the initial vorticities on the collision energies is reconfirmed and the turning point is 10-15 GeV for different vorticities. The global $\Lambda$ polarization at energies $\sqrt{S_{NN}}$ = 7.7--200 GeV is reproduced by introducing an energy density freeze-out criterion.