High Resolution
Numerical Simulations of Bidisperse Particle-Driven Gravity Currents
Hoyes, James R.1, Lionel
Elliot1, Derek B. Ingham1, William D. McCaffrey1,
Jeff Peakall1, Mohammed Pourkashanian1 (1)
High resolution, three-dimensional Direct
Numerical Simulations (DNS) have been performed to investigate the internal
dynamics of bidisperse particle-driven gravity currents. Particular interest is
given to the manner in which fine and course particles segregate within the
flow leading to particle size stratification in the resultant deposits.
Differences between the flow characteristics of mono and bidisperse currents
are analysed three-dimensionally and it is shown that the bidisperse case
cannot be approximated by a monodisperse current. Results are rigorously
compared with predictions from shallow water theory and experimental data and
shown to be in good agreement. The validity of one-dimensional box and shallow
water models, which assume no vertical stratification in the flow, are
discussed in light of the fully resolved DNS results.
The simulations were performed using
second order numerical algorithms within the commercial software package FLUENT
and run on a large parallel computing cluster. The density difference between
particle-laden and ambient fluids was assumed to be small (< 5%) allowing
use of the Boussinesq approximation. Low volumetric particulate concentrations
meant that particle-particle interactions such as hindered settling could be
neglected. Particles had low Reynolds number and were therefore assumed to be
convected by the buoyancy induced fluid motion, and settle vertically with a
constant settling velocity. Simulations were performed at Reynolds number of
the order of 1000, gravity currents propagating at this Reynolds number have
been shown to be ‘similar' to those propagating at higher Reynolds numbers.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California