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Initial values not taken into account ?

Posted Nov 29, 2018, 11:42 a.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD), Microfluidics 2 Replies

Pauline Riviere
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Hi all,

I hope everything's well for you ! I am fairly new to COMSOL and I am performing a CFD simulation with laminar flow and biphasic flow with level set method. As I am studying the filling of my geometry, I use a time dependant study.

I am facing an issue with the simulation : - I assigned a first step of initial value in my first domain with my material that will fill the cavity (u = 3mm/s et a pressure at 1) - I assigned a second step of initial value for the air present in the cavity where nothing happens at time t=0s (everything is at 0)

However in my results, it seems that only the initial values of my first domain are taken into account in all the geometry, and I cannot really understand why. Has anybody faced the same issue and can maybe give me some advice on this ?

I hope I have been clear enough ! Here are some photos of my geometry : - The first one shows the speed at time t=0s where I think I should see no speed in he second domain - The second one is to show the two domain I am working with Thanks in advance for your help !

2 Replies Last Post Dec 3, 2018, 5:54 p.m. EST
Michael Rembe Certified Consultant
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Posted: 6 years ago Nov 30, 2018, 9:17 a.m. EST

Hi Pauline, please explaine it little more detailed. I don't understand the sense of your steps 1 and 2. Do you mean study steps? In this case you have to set the "Values of dependent variables" correctly.

You can control the initial value by "Get initial value for step".

Best regards Michael Rembe

-------------------
Michael Rembe
Rembe Consulting PartG mbB
www.rembe-consulting.de


Hi Pauline, please explaine it little more detailed. I don't understand the sense of your steps 1 and 2. Do you mean study steps? In this case you have to set the "Values of dependent variables" correctly. You can control the initial value by "Get initial value for step". Best regards Michael Rembe
Pauline Riviere
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Posted: 6 years ago Dec 3, 2018, 5:54 p.m. EST

Hello Mr Rembe,

Thanks a lot for your answer ! I took a little bit of time to answer back because i was trying to do what you told me.

First off i will try to clarify my issue :

I put some photos to illustrate the method and the different steps I used for the laminar flow part of the study, i hope it will be clearer. It is in french but i will put the translation here :

(see forumComsol3.png) Laminar flow (spf) - Fluid properties 1 - Initial values 1 (see forumComsol4.png) - Wall 1 - Wall 2 - Fluid properties 2 - Initial values 2 (see forumComsol5.png) - Inlet (see forumComsol6.png) - Outlet (see forumComsol8.png)

Level set (ls) - Level set model 1 - Initial values 1 - No flow 1 - Level set model 2 - Initial values 2 - Inlet (see forumComsol6.png) - Initial interface (see forumComsol7.png) - Outlet (see forumComsol8.png)

So my initial values 1 has the velocity u = 0 m/s and the pressure p = 0 Pa, and my initial values 2 has the velocity u = 0.03 m/s, and the pressure p = 1 Pa. This is what I meant when I talked about steps. I thought that it would be logical to have a speed equal to zero in the bigger domain since I have initial values at 0 in it, however the results seem to show that I have a speed near 0.03 m/s in all of the geometry at time t=0s (see forumComsol.png). So this is my issue.

I tried to set the "values of independant variables" correctly as you told me, but my firt trials are not successful for the moment.

Thanks again for your help! I you've got any more ideas or advice to give me I am fully open to it :)

Have a nice day!

Best Regards, Pauline RIVIERE

Hello Mr Rembe, Thanks a lot for your answer ! I took a little bit of time to answer back because i was trying to do what you told me. First off i will try to clarify my issue : I put some photos to illustrate the method and the different steps I used for the laminar flow part of the study, i hope it will be clearer. It is in french but i will put the translation here : (see forumComsol3.png) Laminar flow (spf) - Fluid properties 1 - Initial values 1 (see forumComsol4.png) - Wall 1 - Wall 2 - Fluid properties 2 - Initial values 2 (see forumComsol5.png) - Inlet (see forumComsol6.png) - Outlet (see forumComsol8.png) Level set (ls) - Level set model 1 - Initial values 1 - No flow 1 - Level set model 2 - Initial values 2 - Inlet (see forumComsol6.png) - Initial interface (see forumComsol7.png) - Outlet (see forumComsol8.png) So my initial values 1 has the velocity u = 0 m/s and the pressure p = 0 Pa, and my initial values 2 has the velocity u = 0.03 m/s, and the pressure p = 1 Pa. This is what I meant when I talked about steps. I thought that it would be logical to have a speed equal to zero in the bigger domain since I have initial values at 0 in it, however the results seem to show that I have a speed near 0.03 m/s in all of the geometry at time t=0s (see forumComsol.png). So this is my issue. I tried to set the "values of independant variables" correctly as you told me, but my firt trials are not successful for the moment. Thanks again for your help! I you've got any more ideas or advice to give me I am fully open to it :) Have a nice day! Best Regards, Pauline RIVIERE

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