---
_id: '112'
abstract:
- lang: eng
  text: Particle beams are important tools for probing atomic and molecular interactions.
    Here we demonstrate that particle beams also offer a unique opportunity to investigate
    interactions in macroscopic systems, such as granular media. Motivated by recent
    experiments on streams of grains that exhibit liquid-like breakup into droplets,
    we use molecular dynamics simulations to investigate the evolution of a dense
    stream of macroscopic spheres accelerating out of an opening at the bottom of
    a reservoir. We show how nanoscale details associated with energy dissipation
    during collisions modify the stream\'s macroscopic behavior. We find that inelastic
    collisions collimate the stream, while the presence of short-range attractive
    interactions drives structure formation. Parameterizing the collision dynamics
    by the coefficient of restitution (i.e., the ratio of relative velocities before
    and after impact) and the strength of the cohesive interaction, we map out a spectrum
    of behaviors that ranges from gaslike jets in which all grains drift apart to
    liquid-like streams that break into large droplets containing hundreds of grains.
    We also find a new, intermediate regime in which small aggregates form by capture
    from the gas phase, similar to what can be observed in molecular beams. Our results
    show that nearly all aspects of stream behavior are closely related to the velocity
    gradient associated with vertical free fall. Led by this observation, we propose
    a simple energy balance model to explain the droplet formation process. The qualitative
    as well as many quantitative features of the simulations and the model compare
    well with available experimental data and provide a first quantitative measure
    of the role of attractions in freely cooling granular streams.
acknowledgement: This work was supported by the NSF through CBET-0933242. We acknowledge
  use of shared facilities provided by the Keck Facility for Ultrafast Imaging at
  the University of Chicago and by the Chicago MRSEC through NSF DMR-0820054. Software
  support by Itasca Consulting Group, Inc., under the Itasca Educational Partnership
  is gratefully acknowledged. H.G. thanks the German-American Fulbright Commission
  for fellowship support during his stay at the University of Chicago.
article_number: '051302'
arxiv: 1
author:
- first_name: Scott R
  full_name: Waitukaitis, Scott R
  id: 3A1FFC16-F248-11E8-B48F-1D18A9856A87
  last_name: Waitukaitis
  orcid: 0000-0002-2299-3176
- first_name: Helge
  full_name: Grütjen, Helge
  last_name: Grütjen
- first_name: John
  full_name: Royer, John
  last_name: Royer
- first_name: Heinrich
  full_name: Jaeger, Heinrich
  last_name: Jaeger
citation:
  ama: Waitukaitis SR, Grütjen H, Royer J, Jaeger H. Droplet and cluster formation
    in freely falling granular streams. <i>Physical Review E</i>. 2011;83(5). doi:<a
    href="https://doi.org/10.1103/PhysRevE.83.051302">10.1103/PhysRevE.83.051302</a>
  apa: Waitukaitis, S. R., Grütjen, H., Royer, J., &#38; Jaeger, H. (2011). Droplet
    and cluster formation in freely falling granular streams. <i>Physical Review E</i>.
    American Physical Society. <a href="https://doi.org/10.1103/PhysRevE.83.051302">https://doi.org/10.1103/PhysRevE.83.051302</a>
  chicago: Waitukaitis, Scott R, Helge Grütjen, John Royer, and Heinrich Jaeger. “Droplet
    and Cluster Formation in Freely Falling Granular Streams.” <i>Physical Review
    E</i>. American Physical Society, 2011. <a href="https://doi.org/10.1103/PhysRevE.83.051302">https://doi.org/10.1103/PhysRevE.83.051302</a>.
  ieee: S. R. Waitukaitis, H. Grütjen, J. Royer, and H. Jaeger, “Droplet and cluster
    formation in freely falling granular streams,” <i>Physical Review E</i>, vol.
    83, no. 5. American Physical Society, 2011.
  ista: Waitukaitis SR, Grütjen H, Royer J, Jaeger H. 2011. Droplet and cluster formation
    in freely falling granular streams. Physical Review E. 83(5), 051302.
  mla: Waitukaitis, Scott R., et al. “Droplet and Cluster Formation in Freely Falling
    Granular Streams.” <i>Physical Review E</i>, vol. 83, no. 5, 051302, American
    Physical Society, 2011, doi:<a href="https://doi.org/10.1103/PhysRevE.83.051302">10.1103/PhysRevE.83.051302</a>.
  short: S.R. Waitukaitis, H. Grütjen, J. Royer, H. Jaeger, Physical Review E 83 (2011).
date_created: 2018-12-11T11:44:41Z
date_published: 2011-05-12T00:00:00Z
date_updated: 2021-01-12T06:48:25Z
day: '12'
doi: 10.1103/PhysRevE.83.051302
extern: '1'
external_id:
  arxiv:
  - '1006.1371'
intvolume: '        83'
issue: '5'
language:
- iso: eng
main_file_link:
- open_access: '1'
  url: https://arxiv.org/abs/1006.1371
month: '05'
oa: 1
oa_version: Preprint
publication: Physical Review E
publication_status: published
publisher: American Physical Society
publist_id: '7942'
quality_controlled: '1'
status: public
title: Droplet and cluster formation in freely falling granular streams
type: journal_article
user_id: 3E5EF7F0-F248-11E8-B48F-1D18A9856A87
volume: 83
year: '2011'
...