Reverse Flow Pressure-Outlet

gustavosimiema · June 23, 2015, 10:00

I think It´s ok, please see the results:

Mass Flow Rate (kg/s)
-------------------------------- --------------------
inlet 1.71e-05
interior-fluid 0.00012537814
outlet_chamber -1.0750113e-05
outlet_gasfeed -7.0932714e-06
wall-fluid -0
---------------- --------------------
Net -7.4338468e-07

pakk · June 23, 2015, 10:09

That does not seem so wrong, although the big number after the interior is a red flag.
But then how can you see all streamlines from the inlet ending up at walls? What happens if you do reverse streamlines from the outlets?

gustavosimiema · June 23, 2015, 10:13

Basically I have to choose the Region, for example I can set the streamline from the outletgasfeed backwards. Than it will Show just streamlines inside the gasfeed. Or I can set the streamlines from the outlet of the chamber backwards. Then I will see lot´s of vortex inside the chamber. And for me, it sounds strange, there is no sense to have vortex in this case.

pakk · June 23, 2015, 10:18

And your residuals are really low enough?

gustavosimiema · June 23, 2015, 10:23

Are lower than 1e-3 but I also tested with more iterations and the residuals stabilized...

The inlet is on the bottom of the gasfeed...

pakk · June 23, 2015, 10:28

I am sorry but I don't understand the geometry. Where is your inlet? Where are your two outlets? How can flow go from the pipe to the chamber?

gustavosimiema · June 23, 2015, 10:35

The gas goes into the gasfeed (pipe) from the inlet. Then the gas get out from the pipe and gent into the chamber through the gasfeed outlet and then the gas come out the chamber through the outlet of the chamber.

It´s more clear?

pakk · June 23, 2015, 10:41

Aha, here is your problem:

Quote:

Then the gas get out from the pipe and gent into the chamber through the gasfeed outlet

No, that is not what an outlet does. If you use an outlet, the gas will go out of your simulation. Not into the chamber...

You said that the streamlines from the input goes to the "top of the pipe". If I look at your picture, that is where you placed the "outlet of the gas feed", so streamlines go from inlet to outlet, as it should.

You should not have those "outlets of the gas feeds" as boundaries. You should just have them as holes in the wall.

gustavosimiema · June 23, 2015, 10:43

Wow NICE

But how can I tell to fluent that there are holes?

pakk · June 23, 2015, 10:46

In the same way you told Fluent there was a pipe: Draw them in your design.

gustavosimiema · June 23, 2015, 10:54

Thank you so much...

I have just started a new Simulation without the boundary gasfeed-outlet. So now I have just the inlet of the gasfeed, the holes and the outlet of the chamber.

The reversed flow persists... let´s see in the end how it would be.

thank you so much...

I´ll let you know when it is finished.

gustavosimiema · June 23, 2015, 11:10

I think didn´t worked...

the streamlines didn´t achieve the outlet. In this case, after convergence I got reversed flow in 37 faces in pressure outlet.

Any idea?

pakk · June 23, 2015, 11:19

Simulate longer. The standard 1e-3 residual is too high for these cases.

gustavosimiema · June 23, 2015, 11:26

Ok...
Now I put 1e-6 and 5000 iterations. Let´s see ...

I let you know when it finishes. Now it will take time...

gustavosimiema · June 24, 2015, 05:42

Hi,

The solution converged after 1256n iterations with residual 1e-6. The reversed flow message disappeared. But when I activate the streamlines I still see lots of vortex inside the chamber before the gas flow to the outlet. Do you have any hint?

Now I have just tried to put operating condition as (1Pa) and the boundary condition as (0Pa) keeping all other Parameters the same but in this way the Mass Diffusivity error appeared. When I initialize the Simulation the Z velocity is 700 m/s and the temperature 7K (this is so strange for me).

What would you suggest for me to do in both cases?

June 23, 2015, 10:23		#25
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Are lower than 1e-3 but I also tested with more iterations and the residuals stabilized... The inlet is on the bottom of the gasfeed... Last edited by gustavosimiema; June 25, 2015 at 02:09.

June 23, 2015, 10:35		#27
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	The gas goes into the gasfeed (pipe) from the inlet. Then the gas get out from the pipe and gent into the chamber through the gasfeed outlet and then the gas come out the chamber through the outlet of the chamber. It´s more clear? Last edited by gustavosimiema; June 25, 2015 at 02:08.

June 23, 2015, 11:10		#32
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	I think didn´t worked... the streamlines didn´t achieve the outlet. In this case, after convergence I got reversed flow in 37 faces in pressure outlet. Any idea? Last edited by gustavosimiema; June 25, 2015 at 02:09.

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June 23, 2015, 10:00		#21
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	I think It´s ok, please see the results: Mass Flow Rate (kg/s) -------------------------------- -------------------- inlet 1.71e-05 interior-fluid 0.00012537814 outlet_chamber -1.0750113e-05 outlet_gasfeed -7.0932714e-06 wall-fluid -0 ---------------- -------------------- Net -7.4338468e-07

June 23, 2015, 10:09		#22
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	That does not seem so wrong, although the big number after the interior is a red flag. But then how can you see all streamlines from the inlet ending up at walls? What happens if you do reverse streamlines from the outlets?

June 23, 2015, 10:13		#23
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Basically I have to choose the Region, for example I can set the streamline from the outletgasfeed backwards. Than it will Show just streamlines inside the gasfeed. Or I can set the streamlines from the outlet of the chamber backwards. Then I will see lot´s of vortex inside the chamber. And for me, it sounds strange, there is no sense to have vortex in this case.

June 23, 2015, 10:18		#24
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	And your residuals are really low enough?

June 23, 2015, 10:28		#26
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	I am sorry but I don't understand the geometry. Where is your inlet? Where are your two outlets? How can flow go from the pipe to the chamber?

June 23, 2015, 10:43		#29
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Wow NICE But how can I tell to fluent that there are holes?

June 23, 2015, 10:46		#30
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	In the same way you told Fluent there was a pipe: Draw them in your design.

June 23, 2015, 10:54		#31
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Thank you so much... I have just started a new Simulation without the boundary gasfeed-outlet. So now I have just the inlet of the gasfeed, the holes and the outlet of the chamber. The reversed flow persists... let´s see in the end how it would be. thank you so much... I´ll let you know when it is finished.

June 23, 2015, 11:19		#33
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	Simulate longer. The standard 1e-3 residual is too high for these cases.

June 23, 2015, 11:26		#34
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Ok... Now I put 1e-6 and 5000 iterations. Let´s see ... I let you know when it finishes. Now it will take time...

June 24, 2015, 05:42		#35
gustavosimiema Senior Member Gustavo Join Date: Jun 2015 Posts: 121 Rep Power: 10	Hi, The solution converged after 1256n iterations with residual 1e-6. The reversed flow message disappeared. But when I activate the streamlines I still see lots of vortex inside the chamber before the gas flow to the outlet. Do you have any hint? Now I have just tried to put operating condition as (1Pa) and the boundary condition as (0Pa) keeping all other Parameters the same but in this way the Mass Diffusivity error appeared. When I initialize the Simulation the Z velocity is 700 m/s and the temperature 7K (this is so strange for me). What would you suggest for me to do in both cases?