How to separate flow in two outputs as 70:30?

Spiros · December 27, 2013, 19:48

Hi. I have a 2d tube. In this tube with diameter D0 i have as inlet a constant velocity U. I call this tube Mother tube.
Then this tube is separated in two smaller tubes (daughter tubes) of different sizes (say D1=D0/2 and D2=D0).
Each output is= "Type:Pressure-outlet" with zero Gauge Pressure and the Backflow direction is set to default "Normal to Boundary".

How can i have a constant flow ratio 70:30 in the outlets of the daughter tubes, of D2(70) and D1(30)??

I try to do it like that in the first daughter tube:
I clicked the "Target Mass Flow Rate" and then in the "Target Mass Flow" box i input the number: 0.3*(A*U*m)
where:
A= area of mother tube
U=Velocity of the fluid in the mother tube
M=mass (Density) of the fluid in mother tube.
And for the other daughter tube i did:0.7*(A*U*m)

Is this the correct way to tell Fluent that i want a flow ration of 70:30 at the two outputs?
Thank you

macfly · December 28, 2013, 13:30

Hi Spiros,

What are the results? Did you obtain the targeted mass flow rates? What pressures Fluent calculated at the outlets? I think your approach is ok, and depending on the shape of your geometry, Fluent will adjust the pressure at the outlets in order to obtain the targeted flow rates.

mrji8011 · December 28, 2013, 14:10

I think by using velocity outlet BC, you can separate them easily. just need to define two Velocity outlet BC with 0.7 and 0.3 outflow rate

Spiros · December 28, 2013, 14:34

Quote:

Originally Posted by macfly

Hi Spiros,

What are the results? Did you obtain the targeted mass flow rates? What pressures Fluent calculated at the outlets? I think your approach is ok, and depending on the shape of your geometry, Fluent will adjust the pressure at the outlets in order to obtain the targeted flow rates.

The results at the outflows where as expected but i get some disturbances (very high velocities) at some points in the beginning of the bifurcation on the site of the smaller tube but i think that's normal. But i was not sure if i my approach of the problem was wright or wrong. Thank you for the reply!

Spiros · December 28, 2013, 14:36

Quote:

Originally Posted by mrji8011

I think by using velocity outlet BC, you can separate them easily. just need to define two Velocity outlet BC with 0.7 and 0.3 outflow rate

Thank you for the reply! I'm running the simulation now and i will see whether that worked for me or not.

Zaktatir · December 29, 2013, 04:38

If you are sure that the flow is fully developed and you are working with incompressible fluid you may use outflow BC with mass weightening (without any pressure level specification at the Boundaries)

December 27, 2013, 19:48	How to separate flow in two outputs as 70:30?	#1
Spiros New Member Join Date: Dec 2013 Posts: 4 Rep Power: 12	Hi. I have a 2d tube. In this tube with diameter D0 i have as inlet a constant velocity U. I call this tube Mother tube. Then this tube is separated in two smaller tubes (daughter tubes) of different sizes (say D1=D0/2 and D2=D0). Each output is= "Type:Pressure-outlet" with zero Gauge Pressure and the Backflow direction is set to default "Normal to Boundary". How can i have a constant flow ratio 70:30 in the outlets of the daughter tubes, of D2(70) and D1(30)?? I try to do it like that in the first daughter tube: I clicked the "Target Mass Flow Rate" and then in the "Target Mass Flow" box i input the number: 0.3(AUm) where: A= area of mother tube U=Velocity of the fluid in the mother tube M=mass (Density) of the fluid in mother tube. And for the other daughter tube i did:0.7(AUm) Is this the correct way to tell Fluent that i want a flow ration of 70:30 at the two outputs? Thank you

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December 28, 2013, 13:30		#2
macfly Senior Member François Grégoire Join Date: Jan 2010 Location: Canada Posts: 392 Rep Power: 17	Hi Spiros, What are the results? Did you obtain the targeted mass flow rates? What pressures Fluent calculated at the outlets? I think your approach is ok, and depending on the shape of your geometry, Fluent will adjust the pressure at the outlets in order to obtain the targeted flow rates.

December 28, 2013, 14:10		#3
mrji8011 New Member mj Join Date: Apr 2011 Posts: 24 Rep Power: 14	I think by using velocity outlet BC, you can separate them easily. just need to define two Velocity outlet BC with 0.7 and 0.3 outflow rate

December 29, 2013, 04:38		#6
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	If you are sure that the flow is fully developed and you are working with incompressible fluid you may use outflow BC with mass weightening (without any pressure level specification at the Boundaries)