Rotational kinematics of large cylindrical particles in turbulence

Abstract

The rotational kinematics of inertial cylinders in homogeneous isotropic turbulence is investigated via laboratory experiments. The effects of particle size and shape on rotation statistics are measured for near-neutrally buoyant particles whose sizes are within the inertial subrange of turbulence. To examine the effects of particle size, three right-circular cylinders (aspect ratio $\unicode[STIX]{x1D706}=1$) are considered, with size $d_{eq}=16\unicode[STIX]{x1D702}$, $27\unicode[STIX]{x1D702}$ and $67\unicode[STIX]{x1D702}$. Here, $d_{eq}$ is the diameter of a sphere whose volume is equal to that of the particle and $\unicode[STIX]{x1D702}$ is the Kolmogorov length scale. Results show that the variance of the particle rotation rate follows a $-4/3$ power-law scaling with respect to $d_{eq}$. To examine the effect of particle shape, two cylinders with identical volumes and different aspect ratios ($\unicode[STIX]{x1D706}=1$ and $\unicode[STIX]{x1D706}=4$) are measured. Their motion also scales with $d_{eq}$ regardless of shape. Simultaneous measurements of orientation and rotation for $\unicode[STIX]{x1D706}=4$ particles allows a decomposition of rotation along the primary axes of each particle. This analysis shows that there is no preference for rotation about a particle’s symmetry axis, unlike the preference displayed by sub-Kolmogorov-scale particles in previous studies.