Geoscience Reference
In-Depth Information
prevailing wind directions in Lisbon (N, NW, and W) and several combinations of
blocks, simulating different roughness lengths (z
0
,
see above) were placed windward
from the model and neutral atmospheric conditions were maintained inside the wind
tunnel [LOP 03; LOP SUB]. Experiments were made for two z
0
windward from the
model: z
0
= 0.02 m (current situation); z
0
= 1.5 m (if the city expands to the NW).
Figure 5.14.
Scale model and wind tunnel [LOP 03]: a) scale model seen from the S; b) scale
model seen from the NW inside the wind tunnel; c) view of the interior of the wind tunnel,
with wooden blocks that simulate the rugosity windwards of the model. They reproduce the
conditions of the UBL. At the bottom the turbines and the scale model; d) detail of the scale
model with the Pitot-Prandtl tube used to determine wind speed (another tube (not seen) at
the top of the model takes measurements of the air layer not disturbed by the surface)
Two examples have been selected from the different experiments carried out by
Lopes [LOP 03]: indirect assessment of wind speed and direction through “erosion
figure technique” and direct assessment of wind speed through the measurement of
airflow inside the scale model. The objective of the “erosion figure technique”
experiment is to monitor the influence of urban fabric on wind direction and speed.
The ground of the scale model is covered with fine sand (diameter <6 ȝm) at the
beginning of the experiment. The sand granules move through saltation. The
observed “erosion patterns” that are visible on the scale model ground may decode
relative wind speeds. Wind direction around and between the buildings was also
assessed by observing, filming and photographing the scale model and the cotton
threads placed inside it. Subsequently, wind speed is progressively increased inside
to wind tunnel for different z
0
values upwind of the scale model, while
measurements of airflow inside the model were carried out (Pitot-Prandtl tubes on
Figure 5.14d), at different heights [LOP 03].
Expansion of the city
Two experiments were carried out for N wind situations in order to compare the
current erosion capability of wind in the city district (with z
0
of 0.02 m upwind of
the model) and a probable future situation within Telheiras, in which z
0
increases up
