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NIST Researchers Explain a Unique Multiphase Flow Phenomenon

January 1999

The transport of small particles through gaseous or fluid wakes is a common phenomenon found in many technological and natural processes in such areas as power generation and pollution control. Approximately a decade ago it was discovered that the conventional wisdom that turbulence in these wakes always results in effective particle mixing is not always true. It was determined that particles in certain size ranges sometimes "demix" by concentrating along the peripheries of the wake vortices, a phenomenon referred to as "focusing." No convincing explanation could be given for this non-intuitive particle behavior, although chaos was sometimes invoked as a controlling factor. Recently, however, a joint CSTL/ITL investigation has elucidated the underlying physical mechanism behind this focusing phenomenon. Utilizing a combination of theoretical and computational techniques, the NIST researchers have conclusively demonstrated that a particle attractor exists in these types of flows and have mapped its behavior as a function of particle size. They have also convincingly demonstrated the important role that centrifugal force effects play in flinging the particles toward the vortex peripheries. Finally, they have proven mathematically that chaos plays no role in this type of particle behavior. The results of this research will be appearing in a paper in the Journal of Fluid Mechanics. The results could ultimately lead to improved designs for such devices as combustors where focusing is clearly a phenomenon to be avoided.

(bullet) Timothy J. Burns (NIST/MCSD/MMG)
(bullet) Ronald W. Davis ()
See also:
(bullet) T. J. Burns, R. W. Davis and E. F. Moore, A Perturbation Study of Particle Dynamics in a Plane Wake Flow, Journal of Fluid Mechanics, to appear. (preprint)

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