[ydima]

Here are some pictures to explain the different named selections that I've created (I've decided to hide some parts for each named selection, in order to be clearer in the visualization).

[AlexanderZ]

does it mean, that you've created real wall of syringe? (shape of water body and shape of syringe wall is different)

show cross section.

zones air and water should have the same material, syringe wall has different material. between air and water there should be some boundary (tip of syringe) with interior boundary condition

explain again, what problem do you have now

best regards

[ydima]

Hi,

Yeah, as I explained you I have sketched my syringe in 3D (with the tip), but it is hollow, so I used the "Fill" tool to create of volume in it.

I've found a solution for my previous issue (air being considered as a solid), but when I display results I still have very weird things. Nothing seems to come out of the syringe into the cube of air I'm pretty sure that I have issues at the interface, but I can't understand why. Like if the software considers that there is a wall blocking the fluid, either at the end of the tip or at the beginning of the air. I am sorry, but I think I've understood your messages well, and I still can't find my error.

I've added a boundary condition on the lower surface of the volume of fluid inside the syringe (check pictures), and it is an interior in the boundary conditions. However, I have the exact same results than when I didn't have it... By the way, as you can see on pictures, the lower surface of the volume of fluid is also the bottom of the hole of the cube of air. Thus, I really don't understand why it doesn't work, because this means that the surface at the bottom of the cube of air and the surface at the bottom of the volume of fluid are actually the SAME, so if it is defined as an interior, I don't understand why the fluid would be blocked. I am actually so lost

I put you again in the pictures some details of the interface between air and syringe. To summarize, I've defined a named selection for the walls of the syringe, and another one for the walls of the air but only on the faces of the cube, not into the hole as you can see on the picture (because I already put walls on the tip in there). I just tried to put walls_air also in the hole (except on surface_tip), still same results! I try to be as clear as possible sorry.. I've enclosed a picture showing the complete list of my boundary conditions, if you see something weird tell me (surface_tip is an interior). I am actually quite desperate right now haha

In my next message I will show you some pictures of my results. If you want I can directly send you my work if you give me your email. I guess it would be easier for you to understand and visualize.

Anyway thank you so much for your time, actually I am in a research group and absolutely nobody here is able to help me on simulations, so you're kind of my only hope.

Yoann

[ydima]

Here are some pictures of the (weird) results. It's like the fluid was under pressure at the top of the syringe, "stable" in it, and compressed against a wall at the bottom (nothing is going in the cube of air). Whatever the velocity inlet and the time step that I choose, I always face this problem.

Yoann

[AlexanderZ]

in boundary conditions go to surface_tip and change type from wall to interior

make sure you have air material in syringe and air zones

best regards

[ydima]

Hi,

As I told you, surface_tip is already an interior...
And I did a multiphase model, like in 2D: water in the syringe and air in the cube below. Why put air in both ? The goal of my work is to see the behaviour of the fluid in the syringe (water here) when going into air. And I think this doesn't change the issue of fluid not going out of the syringe. Do you have other solutions please?

Thank you
Yoann

[AlexanderZ]

you should put air everywhere, but in syringe you put water later, after INITIALIZATION using PATCH tool

best regards

[ydima]

Actually it's already what I've done...

Do you have any other ideas to solve the issue at the interface?

Yoann

[AlexanderZ]

upload you case here

best regards

[ydima]

I can't upload it here, I need your email address. Send me it by private message if you want

[ydima]

Hey,

I post here again because I really can't find any solution for my problem... I decided to slice everything in half to have a better visualization. However, I have a really weird a problem at the end of the tip (at the interface; oh what a surprise ). The water from the syringe is perfectly going down at the top, but at the end of the tip it doesn't go down, and on the contrary, it goes up! It's like the air from the cube is going up in the syringe... But I can't understand how is it possible, if some water is going down at the top and going up at the end, we should have losses right ?? Where is the water missing going ? Please check the pictures I've enclosed. I have created a named selection at the interface as an interior (like it worked so well in 2D), and when I only display this, the behavior is also really weird, there is like water and air at the beginning, but gradually water is disappearing and air occupies more and more space (I put 2 pics showing the evolution of surface_tip and body_air).

Can someone help me please ?

Yoann

[ydima]

Here are pictures of the geometry + named selections.

[ydima]

And more details for the named selections.

[AlexanderZ]

switch off node values, when you plot contours

your pictures of results are confusing, just several rectangular

regarding your model, because you've created real wall of syringe -> now you may delete surface on the tip called surface_tip. You can do it if you give the same material (air) for both zones body_air and body_fluid
interior boundary will be created automatically (but it would be better if you check this)

best regards

[ydima]

Hey,

Thank for your quick reply again! So I did everything that you told me to do, and yes indeed after deleting surface_tip I have an interior body_air-body_fluid (see picture enclosed). I have also checked, and yes I have air everywhere before doing the patch thing to put water in the syringe, so everything works fine. I have some fluid going out of the syringe into air actually, but this is such a small quantity that I am not really sure of the relevance of the results. I mean in 2D a very large quantity of water was coming into air, whereas here it's very limited, even if the level at the top of the syringe is coming down correctly... Morever, unlike the results in 2D, here it seems that I have air coming into the syringe (check the pictures). It's really weird, because in reality water into air should leak very easily, and here water seems so viscous into air.

I don't really know what to change here... I tried with "Steady" and "Transient", I have close results. Maybe the mesh is responsible for the issue at the end of the tip? Do you have some ideas please?

Thanks again!!
Yoann

[AlexanderZ]

check you boundary conditions, in "inlet" boundary you should define water as fluid

best regards

[ydima]

Hi,

Indeed it was a mistake from me! I had a volume fraction of 0 for water in the inlet, instead of 1... Thanks a lot for thinking about that!

However I still have the issue at the end of the tip Even if I put a velocity inlet of 1000m/s (which is huge), I just have a small quantity going out of the tip for a steady problem, and it remains in the tip for a transient problem (see pictures: first for steady and second for transient). Any other ideas please?

Thanks.
Yoann

[AlexanderZ]

use pressure inlet boundary condition in "inlet" not velocity inlet, vary pressure

best regards

[ydima]

Hi,

I've changed for pressure-inlet, but I'm not really sure which values I should put here (check picture). For a default Operating Condition (around 100000 Pa) and a Specified Operating Density of 0kg/m3, I've chosen a Gauge Total Pressure of 0Pa and an Initial Gauge Pressure of 0Pa as well. I've also tried an Operating Condition of 0Pa, a Gauge Total Pressure of 100000Pa and an Initial Gauge Pressure of 0Pa. In both cases, I have the same issue, just a small quantity of water going out of the syringe and air going up in the syringe... It's really like if air was trying to resist, this is so weird

I also see during the iterations the following messages: reversed flow in xx faces on pressure-inlet 15, and this number is not going down, just fluctuating.

Maybe I've defined my values for the inlet wrong?

Thank you.
Yoann

[AlexanderZ]

use Operating Condition of 0Pa (it doesn't matter)
Gauge Total Pressure of 500000Pa and an Initial Gauge Pressure of 0Pa
switch off Specified Operating Density

reversed flow in inlet is not normal.
Play with time step size

best regards