NDLI: Velocity Adjustment and Passive Scalar Diffusion in and Above an Urban Canopy in Response to Various Approach Flows

Content Provider	Springer Nature Link
Author	Kanda, Isao Yamao, Yukio
Copyright Year	2011
Abstract	We used wind-tunnel experiments to investigate velocity-field adjustment and scalar diffusion behaviour in and above urban canopies located downwind of various roughness elements. Staggered arrays of rectangular blocks of various heights H and plan area ratios λp were used to model the urban canopies. The velocity field in the roughness sublayer (height $${z \lesssim 2H}$$ ) reached equilibrium at distances proportional to $${\sqrt{L_{\rm c}H}}$$ where L c is the canopy-drag length scale determined as a function of λp and the block side length L. A distance of about $${20\sqrt{L_{\rm c}H}}$$ was required for adjustment at z = H/2 (in the canopy), and a distance of about $${10\sqrt{L_{\rm c}H}}$$ was required at z = 2H (near the top of the roughness sublayer). Diffusion experiments from a ground emission source revealed that differences in upwind roughness conditions had negligible effects on the plume growth near the source (up to a few multiples of L from the source) if the source was located at a fetch F larger than about $${10\sqrt{L_{\rm c}H}}$$ from the upwind edge of the canopy. However, at locations farther downwind (more than several multiples of L from the source), upwind conditions had considerable effects on the plume growth. For a representative urban canopy, it was shown that a much larger fetch than required for velocity-field adjustment in the roughness sublayer was necessary to eliminate the effects of upwind conditions on plume widths at 24L downwind from the source.
Starting Page	415
Ending Page	441
Page Count	27
File Format	PDF
ISSN	00068314
Journal	Boundary-Layer Meteorology
Volume Number	141
Issue Number	3
e-ISSN	15731472
Language	English
Publisher	Springer Netherlands
Publisher Date	2011-08-21
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Adjustment Diffusion Roughness change Urban canopy Wind tunnel Atmospheric Protection/Air Quality Control/Air Pollution Meteorology/Climatology
Content Type	Text
Resource Type	Article
Subject	Atmospheric Science

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