Translational and rotational dynamics of a large buoyant sphere in turbulence

TL;DR

This study experimentally investigates the translational and rotational behaviors of a large buoyant sphere in isotropic turbulence, introducing a novel visual method for simultaneous position and orientation measurement.

Contribution

It presents an efficient, scalable method for determining the absolute orientation of a sphere from visual data without needing reference images.

Findings

Differences observed between streamwise and transverse translational dynamics.

Evidence of periodicity in translational motion under turbulence.

Angular accelerations show wide tails without directional dependence.

Abstract

We report experimental measurements of the translational and rotational dynamics of a large buoyant sphere in isotropic turbulence. We introduce an efficient method to simultaneously determine the position and (absolute) orientation of a spherical body from visual observation. The method employs a minimization algorithm to obtain the orientation from the 2D projection of a specific pattern drawn onto the surface of the sphere. This has the advantages that it does not require a database of reference images, is easily scalable using parallel processing, and enables accurate absolute orientation reference. Analysis of the sphere's translational dynamics reveals clear differences between the streamwise and transverse directions. The translational auto-correlations and PDFs provide evidence for periodicity in the particle's dynamics even under turbulent conditions. The angular autocorrelations show weak periodicity. The angular accelerations exhibit wide tails, however without a directional dependence.