Thanks for sharing your results - always nice to see the workbench in use.Crossleyuk wrote: ↑Tue Nov 10, 2020 12:40 pm Quick update on my progress into my still shallow understanding of CFD and blueCFD/OpenFOAM
After another six months of torture I have a model that I think is now very close to the geometry of the historic device that I've been trying to obtain a CFD characteristic copy of. Following my observation that it was giving me what looked like a mirrored version of the empirical characteristic.
The latest version of my model has resulted in a characteristic that is in close agreement with the historic empirical version, when mirrored.
As I hope, we can agree the mirroring looks to be very acceptable from the new model and seems to be the way for me to move forward until I can fully explain it. I am now pretty sure that this is indicating that CFD is producing an exit vortex core that is generating a low pressure at the diffuser entry and pulling additional flow from the axial supply inlet. This may be being supported by the Glyph image that is showing dominant radial flow rather than the vortex that I expect and should be a product of the resulting mirrored characteristic.
I cannot explain this and I'm not calling the coding into question, just my understanding of how to apply it. And of course any comments and thoughts are dramatically welcomed by this still novice CFD guy :?
Many Thanks and I'm happy to remove this if it does not fit in with the Forum's intentions.
Are you using pressure boundaries for your inlets? If that is the case, potential flow initialisation will fail. Potential flow is an approximate solution to the flow equations which ignores viscosity (among other approximations), in the absence of which there may be no solution for the prescribed pressure drop (think of a stright, uniform pipe - these will be no pressure drop in the absence of viscosity).Crossleyuk wrote: ↑Thu Dec 10, 2020 3:47 pm Hello All, I've reached the next lack of understanding stage
Another step forward after a thought regarding the selection of Turbulent or Laminar model selection. It turns out that I had been using RANS Turbulence and conducted a Reynolds Number check that suggested Laminar.
Got what I took was a better result that was closer to expected measured characteristic curve but still required mirroring so decided to look at other options including "Initialise Internal Flow Variable" (IFV).
IFV had been chosen as "Specify Values" but I had left them all as default zero values. So entered values that were close to the expected starting values and the result was very poor.
So tried "Potential Flow# with no real understanding. This failed completely with the following reports:
MJC Case_03 Potential Flow Log - Rev P1.pdf
Sorry to trouble you and dont expect solutions but comments would be gratefully received.
Does anybody know how this thing works?johan wrote: ↑Wed May 31, 2017 2:16 pm Just to add to Oliver, for the cut-cell Cartesian mesh generators the CFD WB write a multi-element stl which contains all the faces of the mesh object and the points are scaled to meters when the STL is written. The WB then performs a similarity check which generates a createPatchDict to rename the patches using the prescribed boundary condition names.
Thank you RatonLaveur!RatonLaveur wrote: ↑Wed Feb 10, 2021 12:49 pm Michael,
Though many experienced users and devs have been able to help you and dedicate time with you. I would like, as a bona-fide lurker, to thank you very much for your persistence and documentation of your work. It is exciting to read your posts and to see your progress, exciting as well as instructive.
So thanks and good luck with your further work in this new year 2021!