Dynamics of finite-size spheroids in turbulent flow: the roles of flow structures and particle boundary layers

TL;DR

This paper investigates how finite-size spheroids behave in turbulent flow, revealing the influence of flow structures and boundary layers on their rotational and translational dynamics through detailed numerical simulations.

Contribution

It demonstrates the significance of flow structures and boundary layers in determining the dynamics of inertial-scale spheroids in turbulence, extending understanding beyond spherical particles.

Findings

Particle accelerations and rotations are influenced by volume-filtered fluid forces and torques.

Particle orientations show preferential alignment with flow structures, affecting fluctuation patterns.

Boundary layers significantly impact angular velocities and rotation modes.

Abstract

We study the translational and rotational dynamics of neutrally-buoyant finite-size spheroids in hydrodynamic turbulence by means of fully resolved numerical simulations. We examine axisymmetric shapes, from oblate to prolate, and the particle volume dependences. We show that the accelerations and rotations experienced by non-spherical inertial-scale particles result from volume filtered fluid forces and torques, similar to spherical particles. However, the particle orientations carry signatures of preferential alignments with the surrounding flow structures, which is reflected in distinct axial and lateral fluctuations for accelerations and rotation rates. The randomization of orientations does not occur even for particles with volume equivalent diameter size in the inertial range, here up to 60 $\eta$ at $Re_{\lambda}=120$. Additionally, we demonstrate that the role of fluid boundary layers around the particles cannot be neglected to reach a quantitative understanding of particle statistical dynamics, as they affect the intensities of angular velocities, and the relative importance of tumbling with respect to spinning rotations. This study brings to the fore the importance of inertial-scale flow structures in homogeneous and isotropic turbulence and their impacts on the transport of neutrally-buoyant bodies with size in the inertial range.