Canopy flow regions

Over/through canopies characteristic regions and flow patterns... 

Figure 2.1 Characteristic features of canopy flows (especially urban canopies). Lo is outer-or meso- (regional) scale on which the canopy affects the dispersion. Lc and L/ are the canopy and inner length scales, respectively. Note that UG is the approach geostrophic wind speed above the boundary layer, UB is the typical wind speed associated with local buoyancy effects, e.g. downslope winds from nearby mountains. Hc is the canopy height and Hc is the standard deviation of building height.

The dynamics of fire growth is strongly influenced by the kinematics of flow through porous vegetation and urban structures (the canopy). The local wind and turbulence environment at the source determines the initial spread of a fire. Wind profiles vary depending upon the density (porosity) of the surrounding objects, their distribution vertically or laterally, the presence of below canopy open regions, and the distance... 

For the canopy consisting only of stems (the crowns were removed), the measurements immediately downstream of 10 and 55 rows (Table 3.2) display only monotonic distributions in the mean longitudinal velocity. The boundary layer height was estimated in two x-locations and shown by line 2 in Fig. 3.33. There are, unfortunately, not enough data for this canopy to reliably confirm that the flow immediately downstream of 55 rows (47 h) is within the main region. 

The matched solutions to the four layers tell us that the shear stress layer and upper canopy layers form a region of adjustment across which the mean flow perturbations... 

One final prediction made by the theory of Finnigan and Belcher, [189] must be mentioned as it turns out to have important consequences for scalar transport. This is that even on hills of low slope, H/L 1 a region of reversed flow will appear within the canopy on the lee side of the hill, if the canopy is sufficiently deep and dense. This is... 

A number of authors, however, have represented forest or urban canopy layers by porous regions of distributed force (or drag) [206, 213, 217, 318, 320, 576, 662], The advantage of such an approach is that it permits inclusion of a canopy sublayer without the use of excessive and costly grid resolution. Yamada [662] and Shaw and Schumann [576] introduced the approach in order to add vegetation to meso-scale models of complex terrain. Jeram et al. [320] used the concept in 2d calculations for inviscid flow and constant eddy diffusivity flow estimates of the up and downwind penetration of flow within simple urban areas. 

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