  The traditional algorithm of collisional process in DSMC method, used for
calculation of velocities of molecules after collision, is based on the
conservation laws for linear momentum and total energy. This algorithm does not
provide conservation of angular momentum with respect to some axis, but for
non-rotating flow this circumstance is insignificant, since the mean value of
angular momentum of such kind of flow is equal to zero. The situation changes
for axisymmetric flow with rotation. In this case the traditional procedure
leads to some internal source or sink of angular momentum that may distort the
flowfield. In the paper the discussed effect is recognized and investigated.
The angular momentum conservative (AMC) algorithm of collisional process is
proposed.
