chtMultiRegionFoam transient case issue
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update--- the time step was too big in the setting. Still not sure how fluent was able to get the right value with the same time step, but Openfoam needs a much smaller (6 magnitudes smaller) time step so that the diffusion number is reasonably small to get accurate results.
All, I am new to OpenFOAM and currently solving a heat transfer problem with two different materials. Here is the model setup: I have a quarter of a sphere with a core and a shell. the initial Temperature is uniform everywhere, and the surface of the sphere is losing heat through convection with constant h. To verify the basic model setup, I set both core and shell to be the same material property, and the Biot number is small enough that the Temperature variation with time should be the same as the results from Lumped Capacitance Method. However, the results from Openfoam case is different from the LCM and Fluent model. I attached a plot to show the difference. https://www.dropbox.com/s/bybbmldj90...ation.png?dl=0 Since I converted the mesh from Fluent, and the Fluent case ran just file, I am guessing this is not a meshing issue. I have checked the material properties many times and they are the same as what I used for LCM and fluent. Any advice would be appreciated! Here is the boundary condition on the surface of the shell: Code:
boundaryField Code:
( Code:
ddtSchemes Code:
solvers One more piece of info: If I run the model for longer time, all three curves will converge to the same final Temperature. |
Oh and this is check mesh info before it was split into two regions:
Code:
Create time Let me know if if you need more info to help out! Thanks! |
Hi, the first thing that is obvious is the following:
Code:
Mesh non-orthogonality Max: 49.726612 average: 13.776316 Quote:
Furthermore, many people are not aware how the numeric works and how the equations are solved » explicit and implicit terms. Are you sure that your energy equation is converged (even the explicit terms) within on time-step? The statement that FOAM needs a time-step which is much smaller compared to ANSYS is a hint that you do wrong things in the numerical stuff if the meshes are identical. |
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