@article{fdi:010079869,
  title = {{A}coustic probing of the particle concentration in turbulent granular suspensions in air},
  author = {van den {W}ildenberg, {S}. and {J}ia, {X}. and {R}oche, {O}livier},
  editor = {},
  language = {{ENG}},
  abstract = {{D}ilute gas-particle suspensions in which the particles are carried by the fluid are found in various industrial and geophysical contexts. {O}ne fundamental issue that limits our understanding of such systems is the difficulty to obtain information on the particle concentration inside these often optically opaque suspensions. {T}o overcome this difficulty, we develop ultrasonic spectroscopy to monitor the local particle concentration phi of glass particles (with diameters d similar to 77 mu m or 155 mu m) suspended in air. {F}irst, we determine the minimal air velocity, {U}, necessary to suspend the particles from the maximum decrease in the transmitted wave amplitude and velocity of ultrasound propagating through the suspension. {N}ext, setting the air velocity at {U}, we increase the mass of particles and monitor acoustically the local solid volume fraction, phi, by measuring the ultrasound wave attenuation coefficient and phase velocity as a function of frequency on the basis of classical scattering and hydrodynamic models. {F}or the frequency ranges and suspensions considered here, the viscous dissipation dominates over scattering and thermal conduction losses. {W}e show that, for a characteristic air velocity {U}, the locally measured phi reaches a critical value, in agreement with a recent study on turbulent gas-particle mixtures. {M}oreover, we find that this critical phi increases with the size of the particles. {F}inally, analysis of the temporal fluctuations of the locally measured solid volume fraction, suggests that high density regions (clusters) are present even in suspensions with concentrations below the critical concentration. {T}his differs from the current hypothesis according to which the critical concentration coincides with the onset of cluster formation.},
  keywords = {},
  booktitle = {},
  journal = {{S}cientific {R}eports - {N}ature},
  volume = {10},
  numero = {1},
  pages = {16544 [12 ]},
  ISSN = {2045-2322},
  year = {2020},
  DOI = {10.1038/s41598-020-73427-z},
  URL = {https://www.documentation.ird.fr/hor/fdi:010079869},
}