Measurement of particle and bubble accelerations in turbulence

TL;DR

This study measures the accelerations of particles and bubbles in turbulent flow using advanced optical techniques, revealing how particle density influences acceleration statistics at high Reynolds numbers.

Contribution

It introduces an extended laser Doppler method for high-resolution tracking of particle accelerations in turbulence, comparing different particle densities and their dynamic behaviors.

Findings

Acceleration variance depends on particle density.

Bubbles exhibit higher accelerations than fluid particles.

Normalized acceleration PDFs are similar across particle types.

Abstract

We use an extended laser Doppler technique to track optically the velocity of individual particles in a high Reynolds number turbulent flow. The particle sizes are of the order of the Kolmogorov scale and the time resolution, 30 microseconds, resolves the fastest scales of the fluid motion. Particles are tracked for mean durations of the order of 10 Kolmogorov time scales. The fastest scales of the particle motion are resolved and the particle acceleration is measured. For neutrally buoyant particles, our measurement matches the performance of the silicon strip detector technique introduced at Cornell University \cite{Voth,MordantCornell}. This reference dynamics is then compared to that of slightly heavier solid particles (density 1.4) and to air bubbles. We observe that the acceleration variance strongly depends on the particle density: bubbles experience higher accelerations than fluid particles, while heavier particles have lower accelerations. We find that the probability distribution functions of accelerations normalized to the variance are very close although the air bubbles have a much faster dynamics.