Civil Engineering Reference
In-Depth Information
Figure 3.11
Effective upwind slope for steep
escarpments.
Figure 3.12
Wind flow over a steep cliff.
An additional complication for steep features is that separations can occur at or down-
wind of the crest (see Figure 3.10). Separated flow was found within the first 50 mheight
above the crest of a 480 m high feature, with an upwind slope of only 0.48 (average angle
of 26°), in both full-scale and 1/1000 scale wind-tunnel measurements (Glanville and
Kwok, 1997). This has the effect of decreasing the mean velocity and increasing the
turbulence intensity, as shown in Figure 3.13.
3.4.5
Effect of topography on tropical cyclones and thunderstorm winds
The effect of topographic features on wind near the ground in tropical cyclones and
thunderstorm downbursts is much less clearly understood than those in the well-
developed boundary layers of large-scale synoptic systems.
Tropical cyclones are large storms with similar boundary layers to extra-tropical
depressions on their outer edges. Near the region of strongest winds, they appear to have
much lower boundary-layer heights—of the order of 100m. Topographic features greater
than this height would therefore be expected to interact with the structure of the storm
itself.
