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September 3, 2010 2:05pm UTC

Heat Transfer and Navier Stokes Oscillation Problem??

Hello,

I've beeen working on COMSOL and simulating natural convection of water in a 2D axial symmetry geometry (rectangular).Before simulating this model, I worked on a tutorial ''Heated water''. Under the information provided in this tutorial, I applied following steps...
After specifiying axial symmetry condition I defined:
- heat tr. boundary conditions as heat flux (by specifying h as 5000).
- initial temperatures and the temperatures at the boundaries.
- Navier Stokes boundary conditions (axial symmetry and no slip conditions) and subdomain settings.

Edges of the wall have no-slip conditions, therefore the denser meshes are needed at the walls of the geometry. Because of that, I used mapped mesh parameters by defining the number of edge elements and element ratio (But I could only get denser meshes at 2 out of 4 boundaries-see attached files).

When I solve the problem with this type of mesh I obtain sharp temperature oscillations at a point which is the coldest point of the geometry. During comparison of simulation data with the data I obtained from an experiment very similar to this model, I get sharp deviations.

How can I get rectangular and denser meshes at each individual boundary?
How can I solve these temperature oscillations? Do you have any suggestion?

Thanks in advance,

Best regards

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