  Gas motions in the hot intracluster medium of galaxy clusters have an
important effect on the mass determination of the clusters through X-ray
observations. The corresponding dynamical pressure has to be accounted for in
addition to the hydrostatic pressure support to achieve a precise mass
measurement. An analysis of the velocity structure of the ICM for simulated
cluster-size haloes, especially focusing on rotational patterns, has been
performed, demonstrating them to be an intermittent phenomenon, strongly
related to the internal dynamics of substructures. We find that the expected
build-up of rotation due to mass assembly gets easily destroyed by passages of
gas-rich substructures close to the central region. Though, if a typical
rotation pattern is established, the corresponding mass contribution is
estimated to be up to ~17% of the total mass in the innermost region, and one
has to account for it. Extending the analysis to a larger sample of simulated
haloes we statistically observe that (i) the distribution of the rotational
component of the gas velocity in the innermost region has typical values of
~200-300 km/s; (ii) except for few outliers, there is no monotonic increase of
the rotational velocity with decreasing redshift, as we would expect from
approaching a relaxed configuration. Therefore, the hypothesis that the
build-up of rotation is strongly influenced by internal dynamics is confirmed,
and minor events like gas-rich substructures passing close to the equatorial
plane can easily destroy any ordered rotational pattern.
