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Turbulent air flow in forest stands: a wind tunnel study Warland, Jon S.


This study used a wind tunnel to examine turbulent flow in thinned forests and downwind of shelterbelts. High frequency measurements of the wind components were made using a Dantec triaxial hot-wire probe. Four thinning treatments were studied, consisting of uniformly spaced model trees with plant area index (PAT) = 4.5, 1.7, 0.7 and 0.4. Turbulence statistics up to the fourth order, as well as results from quadrant analysis and spectral densities, were compared to a similar field study, showing good agreement between model and field results. Length and time scales associated with the canopy turbulence were described with linear stability theory. Forest thinning was shown to increase turbulent energy and momentum transport within the canopy. Four shelterbelt widths were studied in both laminar and turbulent flows. Profiles were measured at both upstream and downstream positions, and without shelterbelts present. Turbulence statistics up to the fourth order, spectral densities and results from quadrant analysis were examined. The turbulent flow cases showed little variation with width due to mixing of the flow by turbulence, while the laminar flow cases showed strong differences between widths extending much further downwind.

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