A pendulum driven by the flow

The motion of a pendulum has been investigated for centuries, but what happen if interaction with a surrounding fluid enters in the picture? We consider a tethered 2D cylinder placed between two parallel plane walls. It is shown that confinement alters significantly the flow dynamics, with a new instability, denoted confinement induced vibration (CIV), which occurs at a Reynolds number much lower than the vortex induced vibration (VIV) critical one. Different behaviors have been observed, depending on the density ratio between the body and the surrounding fluid.

For smaller values of the confinement the CIV regime disappears  and it is  replaced instead by a steady asymmetric bifurcation, which we called confinement induced divergence (CID).

Related publications:

Andrea Fani, Francois Gallaire: The motion of a 2D pendulum in a channel subjected to an incoming flow. In: Journal of Fluid Mechanics, 764 , pp. 5–25, 2015.

 

Stability map for a strongly confined cylinder.
Stability map for a strongly confined cylinder.
Stability map for a moderately confined case.
Stability map for a moderately confined case.