Making droplets glow in turbulence

Journal article (2020)

Authors

Humberto Bocanegra Evans Purdue University, Eindhoven University of Technology
Nico Dam Eindhoven University of Technology
Guus Bertens Eindhoven University of Technology, Max Planck Institute for Dynamics and Self-Organization
W. van de Water Eindhoven University of Technology, Fluid Mechanics - Mechanical, Maritime and Materials Engineering
Research Group
Fluid Mechanics (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2020 Humberto Bocanegra Evans, Nico Dam, Guus Bertens, W. van de Water
DOI: https://doi.org/10.1103/PhysRevFluids.5.044303
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Published Date

2020

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Process and Energy

Research Group

Fluid Mechanics

Abstract

We present a new technique to study preferential concentration of droplets in a turbulent air flow. Preferential concentration is the tendency of droplets to cluster in regions of strain, while avoiding regions of rotation. We study the properties of the droplet concentration field in zero mean flow turbulence that was created using an array of synthetic jets. The droplets are made of a phosphorescent solution of Europium chelate. They are excited by a laser sheet from a pulsed UV laser, after which the glowing droplets are followed using a high-speed intensified camera. We quantify preferential concentration through measurement of moments of the coarse-grained local droplet density. At the Stokes numbers studied (St≈2) the fractal dimension, a scaling property of this coarse-grained density field, points to clustering. Clustering is a consequence of the compressibility of the droplet velocity field. We also quantify the dynamical behavior of clustering by moving with this velocity field. We find a preference for clustering in the Lagrangian frame during the time interval set by the decay of the phosphorescence.