Wind tunnel model of the forest and its Reynolds number sensitivity

A newly designed reduced-scale forest model for Wind Engineering and forest meteorological wind tunnel studies is presented. The Reynolds number dependence of flow at the top of and above the forest canopy was investigated for simulated atmospheric boundary-layer flows with different free stream velocities. For the windward edge region, including a downstream distance of 5.7 tree heights, the flow field of the mean streamwise velocity was identified to be independent of the Reynolds number at Reh ≥ 31,000 (Reh based on undisturbed approach flow velocity at canopy top) and at Reh ≥ 50,000 for further flow quantities (fluctuation velocity, Reynolds stress, vorticity, turbulence kinetic energy, shear production). The dependence for lower Reynolds numbers was attributed to differences in the structure of small-scale wakes arising from flow and separation in and at the top of the forest canopy and to a change in the ratio of bulk momentum of the flow in the forest canopy to that of the flow above in the free air region. The threshold Reynolds number Reh,t depends on the distance from the leading edge as long as the flow still adjusts to the forest canopy before reaching the equilibrium region, rather than being a fixed value.