  The tumbling dynamics of individual polymers in semidilute solution is
studied by large-scale non-equilibrium mesoscale hydrodynamic simulations. We
find that the tumbling time is equal to the non-equilibrium relaxation time of
the polymer end-to-end distance along the flow direction and strongly depends
on concentration. In addition, the normalized tumbling frequency as well as the
widths of the alignment distribution functions for a given
concentration-dependent Weissenberg number exhibit a weak concentration
dependence in the cross-over regime from a dilute to a semidilute solution. For
semidilute solutions a universal behavior is obtained. This is a consequence of
screening of hydrodynamic interactions at polymer concentrations exceeding the
overlap concentration.
