Bubble flow and water surface modeling

sloshing · August 7, 2019, 07:06

I analyze the free surface of water when a part of the container is filled with water and bubbly flow is introduced from the bottom. There are two phases, liquid water and air. It is necessary to model the free surface as a sharp interface and the bubble flow as a dispersed interface.

The phenomenon can be reproduced to some extent by using the Multi-Fluid VOF model and "dispersed" as the interface modeling type. On the other hand, the behavior of the free liquid level is still not fully reproduced.

Is there a good modeling technique for both bubble flow and free surface?

esma · August 21, 2019, 04:44

From your description, the water surface appears to be quite stationary since you are introducing air from bottom. Subject to the bubble size diameter I think VOF with sharp/dispersed interface satisfy both your immiscible surface and the bubble rising. The other option is Euler+MFVOF but I think the solution takes much longer.

sloshing · August 23, 2019, 02:25

Thank you for your reply.

In my system, free liquid surface is deformed unsteadyly since the water is shallow. Since the oscillation of the free surface is generated by bubbles, the bubble size and continuous bubble flow are considered important. Should I use VOF model with sharp / dispersed interface in this case as well?
I think, in the vof model with sharp / dispersed interface, the bubble size cannot be set and the continuous bubble flow cannot be reproduced.

esma · August 24, 2019, 04:13

"the bubble size cannot be set " sorry I don't understand how you plan to introduce the secondary phase (air). Usually, you specify an inlet at the boundary and provide an inlet velocity or flow rate for the secondary phase and the bubble size and shape produced are calculated with surface tension between the phases unless you want to model the bubbles individually and let them float! What I understand the diameter indicated for secondary phase in Mixture and Eulerian methods is to provide a mean diameter to take into account for the drag force between the phases. (i.e. air bubble spheres moving through the continues phase). And if the application needs to include drag/lift forces apart from surface tension yes VOF on its own doesn't give that option. So I think in that case an Eulerian coupled with MF VOF can be a good model. But I remember the calculation took much longer than VOF due to more complex equations.

August 7, 2019, 07:06	Bubble flow and water surface modeling	#1
sloshing New Member RYOHEI AOKI Join Date: Aug 2019 Location: Tokyo Posts: 2 Rep Power: 0	I analyze the free surface of water when a part of the container is filled with water and bubbly flow is introduced from the bottom. There are two phases, liquid water and air. It is necessary to model the free surface as a sharp interface and the bubble flow as a dispersed interface. The phenomenon can be reproduced to some extent by using the Multi-Fluid VOF model and "dispersed" as the interface modeling type. On the other hand, the behavior of the free liquid level is still not fully reproduced. Is there a good modeling technique for both bubble flow and free surface?

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August 21, 2019, 04:44		#2
esma Member Join Date: May 2016 Posts: 40 Rep Power: 10	From your description, the water surface appears to be quite stationary since you are introducing air from bottom. Subject to the bubble size diameter I think VOF with sharp/dispersed interface satisfy both your immiscible surface and the bubble rising. The other option is Euler+MFVOF but I think the solution takes much longer.

August 23, 2019, 02:25		#3
sloshing New Member RYOHEI AOKI Join Date: Aug 2019 Location: Tokyo Posts: 2 Rep Power: 0	Thank you for your reply. In my system, free liquid surface is deformed unsteadyly since the water is shallow. Since the oscillation of the free surface is generated by bubbles, the bubble size and continuous bubble flow are considered important. Should I use VOF model with sharp / dispersed interface in this case as well? I think, in the vof model with sharp / dispersed interface, the bubble size cannot be set and the continuous bubble flow cannot be reproduced.

August 24, 2019, 04:13		#4
esma Member Join Date: May 2016 Posts: 40 Rep Power: 10	"the bubble size cannot be set " sorry I don't understand how you plan to introduce the secondary phase (air). Usually, you specify an inlet at the boundary and provide an inlet velocity or flow rate for the secondary phase and the bubble size and shape produced are calculated with surface tension between the phases unless you want to model the bubbles individually and let them float! What I understand the diameter indicated for secondary phase in Mixture and Eulerian methods is to provide a mean diameter to take into account for the drag force between the phases. (i.e. air bubble spheres moving through the continues phase). And if the application needs to include drag/lift forces apart from surface tension yes VOF on its own doesn't give that option. So I think in that case an Eulerian coupled with MF VOF can be a good model. But I remember the calculation took much longer than VOF due to more complex equations.