Basic bluff-body aerodynamics - Wind Loading of Structures - page 92

As the angle of attack, α, increases, the normal force coefficient, C N , progressively
increases towards the normal plate case ( α =90°), discussed in Section 4.3.1, with the
centre of pressure at a height of 0.5 h . For example, the normal force coefficient for an
angle of attack of 45° is about 1.5, with the centre of pressure at a distance of about 0.4 h
from the leading edge, as shown in Figure 4.7. The corresponding values for a equal to
30° are about 1.2 and 0.38 h (ESDU, 1970).
Figure 4.7 Normal force coefficients
for an inclined two-dimensional plate.
Figure 4.8 Area-averaged mean pressure
coefficients on walls and hoardings for oblique
wind directions.
Now, we will consider finite length walls and hoardings, at or near ground level, and
hence in a highly sheared and turbulent boundary-layer flow. The mean net pressure
coefficients at the windward end of the wall, for an oblique wind blowing at 45° to the
normal, are quite high due to the presence of a strong vortex system behind the wall.
Some values of area-averaged mean pressure coefficients are shown in Figure 4.8; these
high values are usually the critical cases for the design of free-standing walls and
hoardings for wind loads.