  Using cosmological N-body simulations we study the radial velocity
distribution in dark matter haloes focusing on the lowest-order even moments,
dispersion and kurtosis. We determine the properties of ten massive haloes in
the simulation box approximating their density distribution by the NFW formula
characterized by the virial mass and concentration. We also calculate the
velocity anisotropy parameter of the haloes and find it mildly radial and
increasing with distance from the halo centre. The radial velocity dispersion
of the haloes shows a characteristic profile with a maximum, while the radial
kurtosis profile decreases with distance starting from a value close to
Gaussian near the centre. We therefore confirm that dark matter haloes possess
intrinsically non-Gaussian, flat-topped velocity distributions. We find that
the radial velocity moments of the simulated haloes are quite well reproduced
by the solutions of the Jeans equations obtained for the halo parameters with
the anisotropy measured in the simulations. We also study the radial velocity
moments for a composite cluster made of ten haloes out to ten virial radii. In
this region the velocity dispersion decreases systematically to reach the value
of the background, while kurtosis increases from below to above the Gaussian
value of 3 signifying a transition from a flat-topped to a strongly peaked
velocity distribution with respect to the Gaussian, which can be interpreted as
the dominance of ordered flow with a small dispersion. We illustrate the
transition by showing explicitly the velocity distribution of the composite
cluster in a few radial bins.
