Two-phase flows are involved in many industrial and natural flow phenomena
varying from as specific as the transport of crude oil in pipelines to as general
as the dispersion of pollutants in the atmosphere. Numerical modelling based
on Computational Fluid Dynamics (CFD), has attracted the attention of
scientists and engineers from a wide range of backgrounds over recent
decades during which these models have been extensively developed, analysed
and applied to many practical applications.
Wind blown particles such as sand or snow and their resulting accumulation
around buildings, roads, oil field installations and security fences causes
severe structural and design problems. These are traditionally addressed
based on previous experience, full-scale field investigation or using scale
model wind tunnel experiments, all of which incur high cost.
In this study, wind blown particles are considered as a two-phase flow system.
A finite volume based CFD code is developed using two-phase flow theory and
is employed to numerically simulate the drifting of sand and snow around
obstacles of different geometry. The model solves the governing transport
equations in three dimensional space. Three different approaches are
investigated to represent and solve the secondary flow phase, particles, within
the flow field; a particle tracking model, based on a Lagrangian reference
frame and the homogenous and the mixture models, based on an Eulerian
reference frame. The capabilities and limitations of each of these models are
investigated for flow fields involving drifting particles around obstacles of
different geometry.
Particles transported by wind both in suspension and saltation are modelled
based on the physical characteristic and the threshold condition of the
particle. Their effect on the flow field is incorporated through separate source
terms contributing to the particle transport equation.
The Eulerian based models are coupled with the Fractional Area/Volume
Obstacle Representation (FAVOR) as a mean of representing the solid boundary formed by deposited particles separating the flow field from the
accumulation zones. The FAVOR treatment allows the flow field to respond to
the changes in the geometry of the deposition regions and further calculations
take into account the erosion and deposition processes that have previously
occurred.
The model can be calibrated to match specific flow conditions through several
controlling parameters. These controlling parameters are identified and
analysed for four distinct case studies. Model results are compared with field
and wind tunnel observations available in the literature and with field
measurements conducted as a part of this study in the desert of the State of
Kuwait. Qualitatively good agreement between the model and the
observations is obtained in two as well as three dimensions.
Although the mixture and particle tracking models show the potential
capability to simulate such flow systems, the homogenous model is found to
be the most appropriate model due to its relative simplicity compared to the
mixture model and its lower computational cost compared to the Lagrangian
particle-tracking model.
In conclusion, a practical CFD tool has been developed and validated,
incorporating novel physical and numerical models. The tool can be utilised
by scientists and engineers to further understand the real world problem of
drifting sand and snow in urban and industrial environments
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