The Venturi effect, named after physicist Giovanni Venturi (1746-1822), is the increase in velocity of a fluid as it travels through a restricted area. Figure 1 below depicts a fluid (air, water, and so on) traveling
at an initial velocity. As the fluid reaches the restricted area
(throat, Venturi), the velocity increases based on the principle
of continuity. As a refresher, the principle of continuity states
that the mass flow through these areas must remain constant.
As the fluid exits the restricted area, the velocity returns to a
more nominal value.
Figure 2 is a view of building showing how the Venturi effect
can cause excessive wind loading to other structures. In Figure
2, the wind velocity profile is shown to the right of the structure. As the wind moves from right to left, a restricted area is
encountered, and the wind velocity increases (Venturi effect).
This causes an increased wind velocity that can damage a building in its path. Even though the open country wind velocity
may not be of sufficient magnitude to damage buildings, those
structures subjected to the Venturi effect may be damaged due
to the increased wind velocity.
Figure 3 shows another way the Venturi effect can damage
a structure. The up slope near the sign tends to restrict the air
flow, causing an increased velocity which can be damaging, despite the existence of nominal open country wind velocities.
Figure 4 shows a sign support column that failed during
strong winds. The arrow shows the imprint of the sign as it fell
downwind. Wind speed at the local airport was approximately
80 mph, which should not have been sufficient to cause the failure of the sign support column. However, the up slope near the
sign was sufficient to accelerate the wind speed to damaging
levels, causing failure of the sign column.
By Charles C. Roberts, Jr.,
The Venturi Effect
Physics at Work in Claims