Coherent structures in multiphase flows

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Abstract

The occurrence of coherent structures in multiphase flows is widespread: quantitative experimental data with respect to their size, their velocities, and their frequency in both bubble columns and fluidized beds are presented; these data have been collected by such different techniques as Laser-Doppler Velocimetry, Particle Image Velocimetry, Optical Bubble Probes, and Gamma- Ray Densitometry. In addition, results are discussed from Computational Fluid Dynamics simulations as to particle swarms in the freeboard beyond bubbling fluidized beds. The question is raised whether there is a common explanation for the appearance of coherent structures in such different systems. The similarity of multiphase flows and natural convection phenomena is discussed, while some features of turbulent multiphase flows resemble those in shear- induced turbulence in single-phase flows. Phase locking, on the basis of interplaying time scales, and an analogy with the vortices in a Karman vortex street are suggested as possible mechanisms behind the occurrence of coherent structures.

Original languageEnglish
Pages (from-to)123-136
Number of pages14
JournalPowder Technology
Volume100
Issue number2-3
DOIs
Publication statusPublished - 1 Dec 1998
Externally publishedYes

Keywords

  • Bubble columns
  • Coherent motions
  • Flow structures
  • Fluidized beds
  • Phase locking
  • Vorticity

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