Hey guys, I realized that when I was running a flow with 2 species, MFiX gave me warnings that some cells have their mass fraction adding up to less than 100% while some more than 100%. Is there a way to access the total mass fraction in each cell so that I can visualize where the mass fractions ar…

You can access the East, North and Top face locations of a scalar cell with use cutcell, only: xg_e, yg_n, zg_t at the top of the routine (with other “use” statements). Then if you want the location in a cell that has I,J,K indices, use XG_E(I) , YG_N(J), and ZG_T(K) . If you need the cell center…

This is only a warning and it is not necessarily a cause for concern. It is fine if you have a very small fraction of cells that are not exactly adding up to one. You can try tightening the linear equation tolerances or switching to the SMART discretization with Chi-scheme correction for the species…

Thank you Jeff! Actually I still need access to all the cell data during training to try out some machine learning projects. Is there a way to do so? Thanks, Jack

Can you read VTK files through your ML code? You can save each species mass fraction in the vtu files. We don’t save the sum, but you could add species together if needed in your code or by modifying vtk_out.f.

I see. Thanks a lot Jeff! I’ll look into vtk_out.f

Hey Jeff, Actually I have a follow up question. Could you help me with it? Thank you! If I extract data from vtu files produced in the simulation (for example u velocity), does it give me the actual u velocity, or does it give me the pixel value? Also could you recommend me some good resources on…

VTK is a very large package and there are a few books that cover it, available for free in PDF format. See Documentation | VTK There are also some Python-specific tutorials and examples at https://kitware.github.io/vtk-examples/site/Python/

MFiX uses a staggered grid for velocity. Each component is stored along the face center (u is stored at the east face, v at the north face in 2D). This can be confusing because Paraview assumes all components are store at the same location. For example, if you have a wall along the east (right) boun…

Thank you Jeff! I noticed that the vtu data are pixel values that ranges from 0 to 255. Is it possible to convert it back to original values of velocity, pressure, and etc?

I think I misunderstood your question about “pixel value”. I was trying the make the point that contrary to scalar quantities (pressure, temperature etc.) which are stored at the center of each cell, the velocity components are stores at the face centers. Now this is probably not what you are asking…

Yeah I think I was getting the cell indices information. I thought all information was stored in cells because I got no point data in my vtu, so I naively used vtk_to_numpy(data.GetCells().GetData()). How should I access the velocity information please? Also, I thought that the cell data relies on …

How to have access to all cell data?

MFiX

jack7z October 13, 2021, 4:38pm 17

Hi Ahjinger,

Yes that was exactly what I was asking. I think this thread might help you.

Jack