[spenceme]

I am running a rather simple 2d model based on the wingMotion tutorial using pimpleFoam. The model goes unstable within 4-5 timesteps and begins what appears to be oscillations from the reported velocity readouts.

I have initialized the pimpleFoam case with the results from a converged simpleFoam run. I am using the same boundary conditions (fixed velocity inlet, slip for top and bottom, inletOutlet with fixed pressure on outlet). The simplefoam results look correct for zero angle of attack.

Chord width is ~.09meters, Velocity is 6m/s. I changed nu to 1.2e-6 (for water). Solution space is ~6meters in length chord direction, and ~2meters in height. Foil is placed at ~1/3 along the length.

Attached is a picture of the time 0 showing the inital velocity field and mesh. I am letting the foil free pivot about a point approx where the red dot is marked. Also attached is a snippet of the pimpleFoam log. I would expect rotation in the positive Z direction based on the pivot location. The model just goes unstable with unrealistic velocities. Also attached is my dynamicMeshDict.

I have tried the following:
-AccelerationDamping factor low from 0.1 to very high/off
-AccelerationRelaxaction factor low and high
-Courant from low (0.02) to high (50+)
-Coarser and finer meshes
-Different damping and spring coefficients

The only item which tends to help is to reduce the rhoInf from 1000 to maybe 10. The model tends to run then and the motion looks to be the correct direction. However the forces are then very low, yet the model still moves quite fast (15 degrees of rotation in .005 seconds??).

I am stuck on what is causing this. Maybe I am missing something simple. Does anyone have some suggestions?