Laser Doppler measurement of inertial particle and bubble accelerations in turbulence

¹  Laboratoire de Physique de l'École normale supérieure de Lyon, CNRS UMR5672 46 Allée d'Italie, 69007 Lyon, France
²  Laboratoire de Physique Statistique de l'École normale supérieure de Paris, CNRS UMR8550 24 rue Lhomond, 75005 Paris, France

Received: 10 October 2007
Accepted: 26 November 2007

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 and their accelerations are measured. For neutrally buoyant particles (fluid tracers), this technique matches the performance of the silicon strip detector technique introduced at Cornell University (Voth G. A. et al., J. Fluid Mech., 469 (2002) 121). This reference dynamics is then compared to that of slightly heavier solid particles (density 1.4) and to air bubbles. We observe that the dynamics of the particles strongly depends on their density. Bubbles have a much faster dynamics and experience much higher accelerations than fluid tracers. Although the particles dynamics are different, we find that the probability distribution functions of accelerations normalized to the variance always remain very close to the one for the fluid tracers.