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10
The wind speed reduction does not remain constant but recovers gradually toward ambient levels as
distance increases downwind. The typical velocity profile behind a porous fence follows this pattern:
Immediate lee (0–
–50% of upwind speed, with
minimal turbulence due to controlled bleed-through flow (key advantage of 50% porosity over
solid barriers).
–10H to 15H): Maximum near-surface velocity suppression (commonly 50–
80% reduction), creating broad low-shear recirculation zones ideal for suppressing particle
entrainment from stockpiles.
Gradual recovery phase (beyond 15H): Wind speeds increase progressively as momentum
–20H, reductions may drop to 20–
40% or less, depending on porosity, wind speed, and site effects—still providing partial benefits
but with diminishing impact on dust generation.
In the context of the Newport News terminals:
Positioning the fence along southern/southwestern perimeters would shelter the bulk of the
northern portions of the piles (closest to sensitive receptors northeast/east).
The gradual recovery ensures that even toward the farther (downwind) edges of the 1,700 ft
span, near-surface winds remain attenuated compared to baseline conditions, reducing overall
fugitive dust potential.
CFD modeling will quantify this profile precisely, incorporating local wind speeds, turbulence, and
coal stockpile interactions to confirm how velocity fields evolve across the site and translate to
emission reductions.
This 18H guideline for 50% porosity thus supports robust coverage across the terminal while
acknowledging the natural, progressive return to ambient airflow—ensuring the design remains effective,
practical, and optimized for community protection.
To explore enhanced protection across the full terminal footprint, sensitivity testing in the CFD study
includes a taller fence height of 100 feet (compared to the baseline 80 feet) for the 50% porous material.
This increase aims to extend the effective downwind shelter zone, better encompassing the
approximately 1,700-foot span of the main stockpile and handling areas under predominant southwest
(SW) winds.
For H = 100 ft:
18H = 1,800 ft
conditions).
Practical effective coverage for robust dust control is estimated at ~1,500–1,700 ft or more
-
specific factors like flat topography, coastal turbulence, and gradual momentum transfer.
The wind speed reduction profile remains gradual rather than abrupt, following a characteristic recovery
curve:
Immediate lee (0–
–500 ft): Strong reduction, often to 20–50% of upwind speeds, with low
turbulence due to porosity.
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