Fluids

Divergence in AMG solver: x-momentum when I change from 2D planar to 2D axisymmetric

• rachels1001
Subscriber

Hey guys,

I have a simulation modelling air flow over a series of pellets of different size. I wanted to model the flow using axisymmetry, with the center of the pellets being along the axis of symmetry (pictured below).

I have a mass-flow inlet at the top of the 2D geometry and a pressure outlet at the bottom. The non-pellet side of the mesh is designated as an adiabatic wall, and the pellet side of the mesh is a symmetry plane.  I initially ran the simulation using the 2D planar setting (incorrectly, had forgotten to make the adjustment) and the simulation was able to run and converge. However, when I switched over to the 2D axisymmetric setting, the simulation was able to initialize; however, I got the error that there was a "divergence in the AMG solver: x-momentum" as soon as it began iterations. This error appeared immediately, before the simulation had completed any iterations.

I tried changing the mass-flow inlet to a velocity-inlet to address the problem; however the same thing occurred. Are there any large changes you have to make to your boundary conditions when you move from 2D planar to 2D axisymmetric?

• DrAmine
Ansys Employee
Can you show the outline of the model. Is flow axisymmetric? Have a defined the x axis to be the symmetry axis?
• rachels1001
Subscriber

^^Outline

The flow is axisymmetric in reality, and I believe the symmetry axis is along the y-axis. Is it required to be the x-axis for 2D axisymmetric?

• rachels1001
Subscriber

To clarify, the y-axis is the axial direction along which flow occurs, and the x-direction is radial. The symmetry axis is running along the y-axis in the positive direction.

• DrAmine
Ansys Employee
Has to be the x-axis.
• Chaymae
Subscriber

Hi

I am facing the same problem though I am using the x-axis.

Regards