Mj. Judd et al., A WIND-TUNNEL STUDY OF TURBULENT-FLOW AROUND SINGLE AND MULTIPLE WINDBREAKS .1. VELOCITY-FIELDS, Boundary - layer meteorology, 80(1-2), 1996, pp. 127-165
This paper describes wind-tunnel experiments on the flow around single
and multiple porous windbreaks (height H), sheltering a model plant c
anopy (height H/3). The mean wind is normal to the windbreaks, which s
pan the width of the wind tunnel. The incident turbulent flow simulate
s the adiabatic atmospheric surface layer. Five configurations are exa
mined: single breaks of three solidities (low, medium, high; solidity
= 1 - porosity), and medium-solidity multiple breaks of streamwise spa
cing 12H and 6H. The experimental emphases are on the interactions of
the windbreak flow with the underlying plant canopy; the effects of so
lidity; the differences in shelter between single and multiple windbre
aks; and the scaling properties of the flow. Principal results are: (1
) the ''quiet zones'' behind each windbreak are smaller in multiple th
an single arrays, because of the higher turbulence level in the very r
ough-wall internal boundary layer which develops over the multiple arr
ays. Nevertheless, the overall shelter effectiveness is higher for mul
tiple arrays than single windbreaks because of the ''nonlocal shelter'
' induced by the array as a whole. (2) The flow approaching the windbr
eak decelerates above the canopy but accelerates within the canopy, pa
rticularly when the windbreak solidity is high. (3) A strong mixing la
yer forms just downwind of the top of each windbreak, showing some of
the turbulence and scaling properties of the classical mixing layer fo
rmed between uniform, coflowing streams. (4) No dramatic increase in t
urbulence levels in the canopy is evident at the point where the deepe
ning mixing layer contacts the canopy (around x/H = 3) but the charact
eristic inflection in the canopy wind profile is eliminated at this po
int.