CFD Online Discussion Forums - Oscillating Cylinder One Way FSI problem

Hi,

I'm trying to simulate a VIV of a circular cylinder. I am using the rigid body 6DOF solver to allow for the oscillation of the cylinder. I have attached an image of my mesh around the cylinder. The region in blue was defined as a subdomain and the motion of the rigid body was imposed on the cells in this region. Cells outside this region were stationary.

This method works well for when the amplitude of oscillation of the cylinder is small. But as soon as the amplitude/cylinder dia ratio becomes greater than 0.3 I get a modulating response as the displacement (figure attached) and the amplitude of oscillation is two orders of magnitude lower than what is required. I am unsure about what is causing this. The Re is 120, the cylinder dia is 1.6mm, fluid is water and the reference values are from Anagnostopoulos and Bearman. The Strouhal number and Cl checked out when I did a transient analysis without FSI, I took a time step of 5e-3, which is 25 steps in one oscillation.

If anyone could help me with this, I would really appreciate it.

Cheers!