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#61 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
you are using symmetry boundary condition on the symmetry plane (oy in your case)
the plane is not important, you may cut your model more (to 1/4 for example) best regards |
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#62 |
Member
Yoann Di Maiolo
Join Date: Jun 2019
Posts: 43
Rep Power: 7 ![]() |
Actually I think I didn't define symmetry anywhere
![]() Is what I did on the picture enclosed enough (defining a symmetry region on all the faces in the plane of symmetry)? Or I also have to select all the faces and create a named selection "symmetry"? Thanks. Yoann |
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#63 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
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you should create a named selection "symmetry"
best regards |
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#64 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Hi,
Okay a short post to give you some news ![]() ![]() Do you have a solution please? ![]() Thank you very much. Yoann |
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#65 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
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from my point of view reversed flows on outlet are ok for your case
best regards |
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#66 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Hi,
As you explained me on another topic, I've decided to slice my model in half to have an axisymmetric thing. Thus, I've used a boolean tool to subtract half of the syringe+air area , and I've defined my boundary conditions the same way as before, but now I've added the axis boundary condition. In Fluent, I've changed Planar to Axisymmetric (don't know what "Axisymmetric Swirl" is). For the rest, I've put all the same parameters. Unfortunately when I try to initialize, I have the following error: "Error: Divergence detected in AMG solver: ads-0 Error Object: #f" When I change pressure-outlet to walls, I can initalize, but when I launch the simulation I have: "Error: Divergence detected in AMG solver: x-momentum Error Object: #f" My mesh looks good enough (check pic enclosed), so I think that this comes from the axis thing. Did I forget something? I've never done that before... Thanks! ![]() Yoann |
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#67 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
axis-body_fluid should be of type axis
do syringe walls have thickness? it is not clear from pictures you have shadow wall between air and syringe wall - which is ok in case you have wall thickness, but there is no shadow between fluid and wall, which is strange check material properties, are they correct? in fluent check mesh quality: General -> check General -> mesh quality check scale best regards |
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#68 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Hi,
Sorry to keep you waiting, I've spent some days to solve the problem (and I did ![]() Walls don't have thickness, and I get what you say about walls, but I think my sketching is fine. ![]() I checked mesh and you said and indeed there was a problem. The software was actually calculating negative volumes, because I wasn't in the y positives. Also, my axis of symmetry wasn't along the x direction, which seems to be a source of problems ![]() ![]() ![]() So I took some days to put all my structure in a better placement, and I have cool results even with a pressure-inlet ![]() I still have issues when I display pressure. I still have reversed flow for pressure-outlet (you told me that this is fine), but also for pressure-inlet after a certain time (you can see on the last picture that the pressure is going crazy at the end, which stops the simulation from running). I don't really know what is the problem here. Moreover, some negative pressures are mentioned in the values on the left, and the pressure seems to go higher in the syringe during the simulation, I don't really know if it's a good thing. Thank you so much for your help ![]() ![]() Yoann |
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#69 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
is you are using operating pressure = 0, then you can get negative pressure. to get the absolute pressure you should add 1 bar
show pressure field on time moments: 0, 1e-05, 1e-04, 2e-04 may be more best regards |
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#70 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Hi,
I'm not sure to understand ![]() Thank you very much. ![]() Yoann |
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#71 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
If you want to have 170000 Pa on inlet (which is absolute pressure), then:
1. You put 170000 Pa on inlet, if your operation pressure is 0 Pa 2. You put 070000 Pa on inlet, if your operation pressure is 101325 Pa same for outlet best regards |
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#72 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
Rep Power: 7 ![]() |
Hi,
Thank you very much for all your help these weeks my friend. You've always been here during 3 months, I can't tell you how grateful I am. How can I thank you? ![]() Yoann |
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#73 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
enjoy your life
best regards |
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#74 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
Rep Power: 7 ![]() |
Hi,
I come back to you because it is my last week of internship. I have worked a lot on the simulation and I have better results now. When I display volume fraction of water, I don't have intermediate values between 0 and 1 now, except at the interface, which is more relevant. However, my flow (water here) is not leaking straight, it tends to go away from the axis of symmetry. Do you have an idea of why please? It is totally non-sense. ![]() Thanks. Yoann |
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#75 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Moreover, when I try to define a shear-thinning fluid, by defining a viscosity following a non-Newtonian Power-Law in the Materials section, the fluid just doesn't get out of the syringe
![]() Do someone have a solution please? Thanks. Yoann |
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#76 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34 ![]() ![]() |
regarding your first question:
if you are using VOF model, you may play with surface tension did you switch on gravity? actually, fluid may go side, because pressure there is lower try to apply more input pressure for the second case unfortunately, I dont have much experience in multi phase flows best regards |
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#77 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
Rep Power: 7 ![]() |
Hi,
Yeah I switched on gravity. I indeed really think that the fluid is going away from the axis because the pressure is lower there, but I CAN'T find why ![]() ![]() ![]() ![]() Thanks. Yoann |
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#78 |
Senior Member
Alexander
Join Date: Apr 2013
Posts: 2,363
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fluid moves through the domain and air "flows" around the fluid. Thats why on the sides of water drop pressure becomes lower.
surface tension should keep fluid in drop shape. This is my vision of your model may be flow speed is too high for surface tension forces. From my point under some conditions your pictures could exist best regards |
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#79 |
New Member
Yoann Di Maiolo
Join Date: Aug 2019
Posts: 12
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Hi,
Can you explain me why the fluid would go where the pressure is lower please? Thanks. ![]() Yoann |
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#80 |
Senior Member
Alexander
Join Date: Apr 2013
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fluid (or gas) flows to region with lower pressure -> this is physics base
same as you changing your route if there is traffic jam ahead from my point of view critical is time of your flow and fluid properties best regards |
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