Problems of VOF model simulating temperature stratified reservoir

Betta · May 6, 2014, 22:15

Hey there,
I am modeling a thermal stratified reservoir, and simplify the temperature structure as two-layer, say layer 1 is 23 $^{\circ}C$ and layer 2 is 20 $^{\circ}C$ .
The geometry model is simple, just a tank with an outlet in the end wall. And I was stuck by how to set the pressure at the inlet(outlet flow rate is known). the flow is supposed as stable.
I tried the VOF model, and I cannot figure out how to get the flow rates of the two layers.
Thank you very much.

ghorrocks · May 7, 2014, 08:19

Please post an image of what you are modelling.

Betta · May 7, 2014, 10:59

Sure.

Thank you to comment.

As shown in the figure, it is a simple tank(can be seen as large reservoir too) with an outlet. I was wondering how can I set inlet pressure B.C(maybe other B.C., I've no idea). for two-layer flow (temperature difference) if I know the outflow rate through the outlet.

And another problem:
Can I use the VOF model provided by CFX to simulate the two layer? I tried in this way but I cannot get the flow rates of the two layers respectively. I used that 'Fluid1.massflow@outlet' or something like this and the warning came out say there was no such thing. So what is wrong with my settings?

Any suggestion will be appreciated.
Thank you all.

ghorrocks · May 7, 2014, 19:41

The free surface multiphase model is used when you have multiple phases (ie gas and liquid). If you have a single phase at different temperatures then just use a thermal model.

Set the temperature at the inlet/opening to a 1D interpolation function or a CEL expression which varies the temperature as a function of height. Simple.

Betta · May 7, 2014, 21:51

Many thanks.
If I set the inlet temperature using CEL, say using STEP function, what the pressure then?
And also the reference density and/or temperature bother me.

Any suggestion about this. Thank you so much for your help.

ghorrocks · May 8, 2014, 00:10

What pressure are you trying to model? If it is open to atmosphere then just zero relative pressure. If it has a flow applied (I suspect it does to generate the thermal stratification you describe) then you need to model a larger volume to model this stratification.

Betta · May 9, 2014, 05:14

thanks a lot for your help and comments.
I will try it again.

May 6, 2014, 22:15	Problems of VOF model simulating temperature stratified reservoir	#1
Betta New Member Betta Hwang Join Date: May 2014 Posts: 6 Rep Power: 12	Hey there, I am modeling a thermal stratified reservoir, and simplify the temperature structure as two-layer, say layer 1 is 23 $^{\circ}C$ and layer 2 is 20 $^{\circ}C$ . The geometry model is simple, just a tank with an outlet in the end wall. And I was stuck by how to set the pressure at the inlet(outlet flow rate is known). the flow is supposed as stable. I tried the VOF model, and I cannot figure out how to get the flow rates of the two layers. Thank you very much.

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May 7, 2014, 08:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Please post an image of what you are modelling.

May 7, 2014, 19:41		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	The free surface multiphase model is used when you have multiple phases (ie gas and liquid). If you have a single phase at different temperatures then just use a thermal model. Set the temperature at the inlet/opening to a 1D interpolation function or a CEL expression which varies the temperature as a function of height. Simple.

May 7, 2014, 21:51		#5
Betta New Member Betta Hwang Join Date: May 2014 Posts: 6 Rep Power: 12	Many thanks. If I set the inlet temperature using CEL, say using STEP function, what the pressure then? And also the reference density and/or temperature bother me. Any suggestion about this. Thank you so much for your help.

May 8, 2014, 00:10		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	What pressure are you trying to model? If it is open to atmosphere then just zero relative pressure. If it has a flow applied (I suspect it does to generate the thermal stratification you describe) then you need to model a larger volume to model this stratification.

May 9, 2014, 05:14		#7
Betta New Member Betta Hwang Join Date: May 2014 Posts: 6 Rep Power: 12	thanks a lot for your help and comments. I will try it again.