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The motion of thin curved falling particles is ubiquitous in both nature andindustry but is not yet widely examined. Here, we describe an experimentalstudy on the dynamics of thin cylindrical shells resembling broken bottlefragments settling through quiescent fluid and homogeneous anisotropicturbulence. The particles have Archimedes numbers based on the mean descentvelocity $0.75 \times 10^4 \lesssim Ar \lesssim 2.75 \times 10^4$. Turbulencereaching a Reynolds number of $Re_\lambda \approx 100$ is generated in a watertank using random jet arrays mounted in a co-planar configuration. After theflow becomes statistically stationary, a particle is released and itsthree-dimensional motion is recorded using two orthogonally positionedhigh-speed cameras. We propose a simple pendulum model that accurately capturesthe velocity fluctuations of the particles in still fluid and find thatdifferences in the falling style might be explained by a closer alignmentbetween the particle's pitch angle and its velocity vector. By comparing thetrajectories under background turbulence with the quiescent fluid cases, wemeasure a decrease in the mean descent velocity in turbulence for theconditions tested. We also study the secondary motion of the particles andidentify descent events that are unique to turbulence such as 'long gliding'and 'rapid rotation' events. Lastly, we show an increase in the radialdispersion of the particles under background turbulence and correlate thetimescale of descent events with the local settling velocity.

Settling behaviour of thin curved particles in quiescent fluid and turbulence