[MSF]

Hello,

I'm simulating a gravity driven film flow over an obstacle with OpenFoam1.6 (Inclination angle 10° and Re between 4 and 30). As a solver a modified version of interFoam is used, so no gravity force acts on the second phase (air). The boundary conditions are cyclic (wave length of the bottom is 2 cm).and the solver settings are taken from the damBreak tutorial, only the Courant Number is decreased to 0,1. For a Mesh consisting of 40000 cells the cases become stationary after about 1 second (see the attached picture) but if i increase the cell number to 160000 the cases are unsteady and something like a standing wave builds up. I do not think that this is physical. Any ideas why increasing the cell number leads to this unsteady behaviour?

Kind regards

Moritz

[massive_turbulence]

Originally Posted by MSF

Hello,

I'm simulating a gravity driven film flow over an obstacle with OpenFoam1.6 (Inclination angle 10° and Re between 4 and 30). As a solver a modified version of interFoam is used, so no gravity force acts on the second phase (air). The boundary conditions are cyclic (wave length of the bottom is 2 cm).and the solver settings are taken from the damBreak tutorial, only the Courant Number is decreased to 0,1. For a Mesh consisting of 40000 cells the cases become stationary after about 1 second (see the attached picture) but if i increase the cell number to 160000 the cases are unsteady and something like a standing wave builds up. I do not think that this is physical. Any ideas why increasing the cell number leads to this unsteady behaviour?

Kind regards

Moritz

If you run the (finer mesh) simulation longer does the system come to equilibrium. I'm thinking your simulation might be more accurate and so the total energy of the system dissipates over a longer period of time?

[MSF]

No the simulation with the finer mesh does not come to an equilibrium. For some Reynolds Numbers it seems like the simulation with the finer mesh is close to an equilibrium but then it starts to oscillate.

[massive_turbulence]

Originally Posted by MSF

No the simulation with the finer mesh does not come to an equilibrium. For some Reynolds Numbers it seems like the simulation with the finer mesh is close to an equilibrium but then it starts to oscillate.

What's your deltaT and endTime?

[MSF]

My deltaT is 6*10^-6s and the endTime is 2.5s.

[massive_turbulence]

Originally Posted by MSF

My deltaT is 6*10^-6s and the endTime is 2.5s.

I was thinking your deltaT might be too large but that looks small to me.