Boundary-Layer Meteorology

, Volume 75, Issue 1–2, pp 141–173 | Cite as

A numerical simulation of boundary-layer flows near shelterbelts

  • Hao Wang
  • Eugene S. Takle


We have developed a shelterbelt boundary-layer numerical model to study the patterns and dynamic processes relating to flow interaction with shelterbelts. The model simulates characteristics of all three zones of airflow passing over and through shelterbelts: the windward windspeed-reduction zone, the overspeeding zone above the shelterbelt, and the leeward windspeed-reduction zone. Locations of the maximum windspeed reduction and recirculation zone, as well as the leeward windspeed-recovery rate are well simulated by the model. Where comparisons with field measurements and wind-tunnel experiments were possible, the model demonstrated good performance for flows over and through shelters ranging from almost completely open to almost solid.

The dynamic pressure resulting from the convergence and divergence of the flow field alters the perturbation pressure field. The disturbed pressure controls not only the formation of the separated flow but also the location of maximum windspeed reduction, streamline curvature, speed-up over the shelterbelt, and leeward windspeed recovery rate. The interaction of pressure with the flow produces complex flow patterns, the characteristics of which are determined, to a great extent, by shelterbelt structure.



Spatial averaged value


Temporal averaged value


Departure of variable from its averaged value


Leaf surface-area density


Atmospheric boundary layer


Drag coefficient for obstacle exerted on air


Drag coefficient for unit plant area density


Experimental constants of turbulent closure scheme (Mellor and Yamada, 1982)


Turbulent kinetic energy (TKE)


Drag force in thei direction exerted on air flow by obstacle elements


Coriolis parameter


Acceleration vector due to gravity


Height of shelterbelt

i, j, k, q

Subscript variables, indicatingx, y andz directions, respectively, and grid numbers in these three directions


Turbulent exchange coefficient for neutral, obstacle-free ABL


Turbulent exchange coefficient for momentum transport


Turbulent exchange coefficient for TKE transport


Resistance coefficient of shelterbelts


Mixing length of turbulence


Mean kinetic energy


Timestep of model integration


Vector and its component in thei direction of the interface of the averaging volume


Atmospheric pressure perturbation


Interface surface of the averaging volume




Total mean windspeed

u, w

Mean windspeed components inx andz directions, respectively

u′, w′

Fluctuating windspeed components inx andz directions


Windspeed in thei direction


Friction velocity


Friction velocity for obstacle-free ABL


u andv at model top

uaux, andwaux

Intermediate prediction velocities ofu andw without the dynamic pressure perturbation

un+1 andwn+1

Prediction velocities ofu andw at then+1 timestep of model integration


Volume of the spatial averaging process


Horizontal coordinate axis perpendicular to shelterbelt


i=1, 2, 3-three direction coordinate,x, y, z


Vertical coordinate axis upward


Ground surface roughness length


Weight coefficient for numerical differencing scheme


Coefficient of air thermal expansion

Dissipation rate of turbulence


Einstein summation symbol


Air density


Potential-temperature departure from its basic state


Coefficient of air molecular viscosity


Time step of model integration


von Karman constant


Macry symbol, standing foru, v, w, E andE1


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Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • Hao Wang
    • 1
  • Eugene S. Takle
    • 1
  1. 1.Department of Geological and Atmospheric Sciences, and Department of AgronomyIowa State UniversityAmesUSA

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