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#1 |
Member
leo
Join Date: Jun 2012
Posts: 98
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These days I do a multi-phase simulation using free surface model and homogeneous model.
At first i do not turn on the surface tension model, it converges badly,and it converges good when i take the surface tension model into consideration. In my simulation,the water and gas interface is well0defined. I am confused why the surface tension force has such a significant role in this simulation. |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Usually the surface tension makes convergence harder, so your application is unusual.
Can you describe what you are modelling, what fluids and what geometry? |
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#3 | |
Member
leo
Join Date: Jun 2012
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Quote:
I wonder why should we take the surface tension force into consideration. What will it influences? |
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#4 |
Super Moderator
Glenn Horrocks
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What type of injector? How big? Is it producing a spray of droplets or some other flow?
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#5 |
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leo
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#6 |
Super Moderator
Glenn Horrocks
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Do you want to simulate the spray break up process directly, or use empirical models (eg LISA)?
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#7 |
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leo
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#8 |
Super Moderator
Glenn Horrocks
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I do not know the details of your model so cannot answer your original question.
However surface tension is critical to spray formation. The droplet formation process is driven by surface tension. So your comment about why you need surface tension is puzzling. |
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#9 | |
Member
leo
Join Date: Jun 2012
Posts: 98
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Quote:
Now ,i am doing the INTERNAL flow simulation,like a pipie, not the spray process.The process before spray in the injector. |
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#10 |
Super Moderator
Glenn Horrocks
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If this is an internal flow then isn't it single phase? Where does the gas/liquid mix come from?
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#11 | |
Member
leo
Join Date: Jun 2012
Posts: 98
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Quote:
It is a pressure-swirl injector, SWIRL means the liquid phase has a tangential velocity after it flows through swirl part (as the picture attached)of the injector. According to the fluid mechanics,the fluid will have low static pressure having tangential velocity. So, in my case, the pressure of the liquid at the exit is lower than the atmospheric air,causing the air flow in the injector,and that helps the atomization process The the mechanism of the pressure-swirl injector. |
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#12 |
Member
leo
Join Date: Jun 2012
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I wish am clear enough.
Thank you again. |
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#13 |
Super Moderator
Glenn Horrocks
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I see. It is hard to know whether surface tension will be important in this or not. If you are close to the injector and before the surface tension has started to form the wobbles which grow and break the sheet up then you might not need it.
So if unsure then I would include it. Be aware that surface tension models require very good mesh quality and much smaller time steps. |
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#14 |
Member
leo
Join Date: Jun 2012
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Thanks sincerely.
CFD is not easy. |
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#15 |
Super Moderator
Glenn Horrocks
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No, it is not easy. That is why it is interesting.
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#16 |
Member
leo
Join Date: Jun 2012
Posts: 98
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Yes.
But,sometimes it drive me crazy when i can not figure it out. Sometimes a small change will lead to much difference and i can not understand it. |
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