  The dynamics of inertial particles in turbulence is modelled and investigated
by means of direct numerical simulation of an axisymmetrically expanding
homogeneous turbulent strained flow. This flow can mimic the dynamics of
particles close to stagnation points. The influence of mean straining flow is
explored by varying the dimensionless strain rate parameter $Sk_0/\epsilon_0$
from 0.2 to 20. We report results relative to the acceleration variances and
probability density functions for both passive and inertial particles. A high
mean strain is found to have a significant effect on the acceleration variance
both directly, through an increase in wave number magnitude, and indirectly,
through the coupling of the fluctuating velocity and the mean flow field. The
influence of the strain on normalized particle acceleration pdfs is more
subtle. For the case of passive particle we can approximate the acceleration
variance with the aid of rapid distortion theory and obtain good agreement with
simulation data. For the case of inertial particles we can write a formal
expressions for the accelerations. The magnitude changes in the inertial
particle acceleration variance and the effect on the probability density
function are then discussed in a wider context for comparable flows, where the
effects of the mean flow geometry and of the anisotropy at the small scales are
present.
