Fluctuation on thermal field with curved boundaries

[vaillant]

Dear all,

In my case I have a rotating cylinder. I am using the Advection Diffusion Boundary Condition to impose a temperature. Unfortunately, I have fluctuations of my temperature field near the wall which are not physical.

Is there a solution to reduce them ?

Thanks in advance

[mathias]

Which values are used for the boundary values? Analytical ones at the surface of off the surface (in the volume)? I would you the values off-surface at thir exact positions. What happens if yoiu refine the mesh?

[vaillant]

For the boundary values I used converter.getLatticeTemperature(298.0). At the surface, depending on the configuration of cells, I found between 296.5 and 300 at the fluid cells. And some points of the boundary, those which are more exposed to the fluid due to the stairway shape, have a value of 302. Sorry I did not understand your third sentence. If I refine the mesh, it reduce the fluctuations but they are still there.

[mathias]

Since they get smaller with finer meshes it seems that the staircase approximation is the reason. You can set a function instead of a constant value at the bounderies depending on there exact position if you have an analytical solution. Then, the fluctuations should be gone.

[vaillant]

Thank you for the advice.

One thing I still don’t understand is how, whereas I fix a constant value to the boundary, some boundary point could be at another value (302 instead of 298). Since we create output with SuperLatticePhysTemperature3D which call this->_blockLattice.get( input[0], input[1], input[2]).computeRho(), we should always have the value that is fixed inside the Momenta, am I right ?

[mathias]

You can create a functor which depends on the exact position and gives you the values (e.g. 300, 302 or whatever) and use it to define the boundary condition. Similarly a quadratic inflow profile is used for a pipe.

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