  Based on the three-fluid model, the global $\Lambda$ polarization in Au+Au
collisions at 2.4 $\leq\sqrt{s_{NN}}\leq$ 7.7 GeV is calculated, including its
rapidity and centrality dependence. Contributions from the thermal vorticity
and meson-field term (proposed by Csernai, Kapusta and Welle) to the global
polarization are considered. The results are compared with data from recent and
ongoing STAR and HADES experiments. It is predicted that the polarization
maximum is reached at $\sqrt{s_{NN}}\approx$ 3 GeV, if the measurements are
performed with the same acceptance. The value of the polarization is very
sensitive to interplay of the aforementioned contributions. In particular, the
thermal vorticity results in quite strong increase of the polarization from the
midrapidity to forward/backward rapidities, while the meson-field contribution
considerably flattens the rapidity dependence. The polarization turns out to be
very sensitive to details of the equation of state. While collision dynamics
become less equilibrium with decreasing collision energy, the present approach
to polarization is based on the assumption of thermal equilibrium. It is found
that equilibrium is achieved at the freeze-out stage, but this equilibration
takes longer at moderately relativistic energies.
