Capture displacement plots

Hello Foamers,
I am trying to simulate Turek FSI3, where i changed the paramters according to my criteria i.e I changed the fluid properties and solid as follows:

Density of solid (ρs) (kg/m3) =32.9
Poisson ratio (νs) =0.199
Young’s Modulus (E) (10^6 kg/m2) =0.849

Density (ρf) (kg/m3) =1.23 (air)
Kinematic Viscosity (νf) (m2/s) =0.0000147
Velocity= 8 ms-1
Thickness of flap= 0.005m

The problem I am facing is, the displacement is very small. Will you all suggest what cfd parametres should be changed to capture large displacement?
PS: I didnt change the timestep size neither courant number.

Hi @daniel

I am not sure I clearly understand your question. You changed the CFD parameters already (density, viscosity, inflow velocity). I did not check your parameters carefully, but I would assume that they simply lead to a steady-state solution.
The original parameters should lead to a periodic movement with rather large displacements.

Hi @uekerman you were right, the solution was leading to steady state this happened when the velocity was low (2ms-1) but when I tried to increase the velocity (4ms-1) the solution started crashing. The openfoam window crashes after reaching a time of 1 second. I tried to decrease the time step but it’s of no help. the maximum courant is very high even after decrasing the timestep. I have attached the displacement plot after the crash and the log file containing the error message.
error.txt (47.9 KB)

I am confused what is actually causing the problem.


Your output shows that OpenFOAM is diverging. This can have many reasons. As your displacement is pretty high I would guess that your mesh gets too distorted. A smaller timestep size does not help in this case.

I am still a bit puzzled what your overall goal is. The FSI3 case will not work for arbitrary parameter combinations. The original configuration does work for you, right?

Thanks @uekerman for your reply. As you asked what my overall goal is ? Well I am working on a research where I am want to observe the FSI of the different materials in air. So I am keeping FSI3 as my base and I am trying to carry forward.
I would be glad, if you guide me how to stabilize the calculation as it’s crashing since the deformation is very high.

Sry for my slow reply.
When the mesh gets too distorted you either need a better mesh mover (which OpenFOAM does not offer AFAIK) or you need to use a larger domain and a larger mesh to spread the distortion more.
For your study, do you actually need the no-slip walls at the bottom and the top? If not, I would recommend removing them and making your domain larger (with a coarser mesh towards the top and bottom).