Mesh symmetry problem

FRibeiro · October 5, 2017, 08:28

Hello everyone,

I’m modeling a micro modular reactor subchannel, which has a hexagonal geometry, but I think we can see this as a cylinder to understand my problem.

I ran a simulation and I had some great results in comparison with analytical ones. But it took really long time, so now I am trying to model just a part of the geometry, since it has some symmetries. For example, I can model 1/6 of the hexagon.

But, using the same mesh refinement (I did a mesh convergence study to the whole subchannel) I’m not finding the same pressure drop: 0,027 MPa (originally) against 0,029 MPa. I tried to increase the refinement by 5 times, but the result does not change.

Do you have any idea what the problem might be? Please.

Thanks,
Felipe

FMDenaro · October 5, 2017, 10:10

Quote:

Originally Posted by FRibeiro

Hello everyone,

I’m modeling a micro modular reactor subchannel, which has a hexagonal geometry, but I think we can see this as a cylinder to understand my problem.

I ran a simulation and I had some great results in comparison with analytical ones. But it took really long time, so now I am trying to model just a part of the geometry, since it has some symmetries. For example, I can model 1/6 of the hexagon.

But, using the same mesh refinement (I did a mesh convergence study to the whole subchannel) I’m not finding the same pressure drop: 0,027 MPa (originally) against 0,029 MPa. I tried to increase the refinement by 5 times, but the result does not change.

Do you have any idea what the problem might be? Please.

Thanks,
Felipe

I assume that you have no bug in setting periodicity in the BC...
However, modelling only 1/6 of the domain is also an assumption on the flow solution. Are you sure that the original complete domain gave you a solution that confirms this assumption?

FRibeiro · October 5, 2017, 10:24

Thank you Denaro,

I am considering Symmetry regions on every fluid face (one because it is a subchannel of a rod bundle, and two because of the 1/6 symmetry).

I don't think I have problems with that, I have been working with rod bundles for a while and I am not considering secondary (transversal) flows, for example.

October 5, 2017, 08:28	Mesh symmetry problem	#1
FRibeiro New Member Join Date: Jan 2014 Posts: 10 Rep Power: 12	Hello everyone, I’m modeling a micro modular reactor subchannel, which has a hexagonal geometry, but I think we can see this as a cylinder to understand my problem. I ran a simulation and I had some great results in comparison with analytical ones. But it took really long time, so now I am trying to model just a part of the geometry, since it has some symmetries. For example, I can model 1/6 of the hexagon. But, using the same mesh refinement (I did a mesh convergence study to the whole subchannel) I’m not finding the same pressure drop: 0,027 MPa (originally) against 0,029 MPa. I tried to increase the refinement by 5 times, but the result does not change. Do you have any idea what the problem might be? Please. Thanks, Felipe

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October 5, 2017, 10:24		#3
FRibeiro New Member Join Date: Jan 2014 Posts: 10 Rep Power: 12	Thank you Denaro, I am considering Symmetry regions on every fluid face (one because it is a subchannel of a rod bundle, and two because of the 1/6 symmetry). I don't think I have problems with that, I have been working with rod bundles for a while and I am not considering secondary (transversal) flows, for example.