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In such studies, CFD models the turbulent airflow around the stockpile geometry (e.g., conical or
trapezoidal piles), the fence (porosity, height, placement, orientation), and particle trajectories via
Lagrangian discrete phase model (DPM). Key inputs include:
Incoming wind speed and direction (often from site-specific wind roses).
Stockpile surface shear stress and threshold friction velocity for particle entrainment.
–1600 kg/m³ for coal dust), size distribution, and release from
the pile surface.
30–50%).
Key Findings on Fence Configurations and Heights
CFD simulations generally show that fence design parameters significantly affect downstream flow
sheltering, reduced surface shear on the pile, and particle capture or redirection. Common configurations
tested include:
–50% (as in classic studies); lower porosity creates stronger
recirculation but risks re-entrainment eddies, while higher porosity allows excessive bleed flow
and reduced shelter.
Height relative to pile: Fences at or above pile crest height (e.g., 1–1.5× pile height) maximize
shelter by deflecting flow over the pile; shorter fences allow flow acceleration over the crest,
increasing erosion on windward/leeward faces.
Placement/orientation: Upstream perpendicular to dominant wind reduces impingement on
piles; multiple fences (e.g., staggered or surrounding) or combinations with barriers enhance
protection. Downwind placement can intercept escaping plumes.
Shape/variations: Straight vertical, curved, inclined, or deflector types; curved or inclined often
perform better by minimizing large wake vortices.
Particle behavior differs markedly due to size-dependent dynamics:
–0.3 m/s) and are more sensitive to near-
surface flow reductions. Fences effectively reduce their emission by:
o
Lowering peak shear stress on windward slopes and crests (often by 40–70%).
o
Creating a low-velocity recirculation zone that traps bouncing particles.
o
Studies show higher reduction rates for coarser sizes (e.g., 60–80% emission cut)
because they are less likely to escape the sheltered zone.
(finer, closer to PM10): These enter true suspension more easily, with lower
–0.01 m/s) and longer airborne residence. They are more influenced by
turbulence and mean flow deflection. Fences reduce their off-site transport by:
o
Decreasing overall plume height and downwind concentration gradients.
o
Reducing turbulence intensity in the wake, limiting vertical mixing.
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