  The statistics of rotational motion of small, inertialess triaxial ellipsoids
are computed along Lagrangian trajectories extracted from direct numerical
simulations of homogeneous isotropic turbulence. The particle angular velocity
and its components along the three principal axes of the particle are
considered, expanding on the results presented by \citet{ChevillardMeneveau13}.
The variance of the particle angular velocity, referred to as the particle
enstrophy, is found to increase for particles with elongated shapes. This trend
is explained by considering the contributions of vorticity and strain-rate to
particle rotation. It is found that the majority of particle enstrophy is due
to fluid vorticity. Strain-rate-induced rotations, which are sensitive to
shape, are mostly cancelled by strain-vorticity interactions. The remainder of
the strain-rate-induced rotations are responsible for weak variations in
particle enstrophy. For particles of all shapes, the majority of the enstrophy
is in rotations about the longest axis, which is due to alignment between the
longest axis and fluid vorticity. The integral timescale for particle angular
velocities about each axis reveals that rotations are most persistent about the
longest axis, but that a full revolution is rare.
