7. Actions perpendicular to the wind direction

Depending on the shape and slenderness of a construction, the Reynolds number characterizing the flow of a fluid around a cylinder can take on a value such as to produce vortex zones acting perpendicular to the wind direction. Above a certain Reynolds number, these vortices detach periodically and alternately (Karman vortices), generating alternating forces on the construction perpendicular to the wind direction (drift forces).

The risk is that the construction will resonate under these forces.

Application to chimney design

It is assumed that the construction is subjected to a periodic drift force, perpendicular to the wind direction, with a triangular distribution, and whose action is assimilated to that of a static force.

Maximum drift force value $$