Divergence due to gas properties.

Sprity Acharya · April 20, 2018, 06:05

Hey everybody!
I have been working on gas flow through a pipe in Fluent. I vary the diameter of the pipe and compare the flow rates in this project. I was using air as the working material and got results. Now I switched to argon and fluent displays divergence detected in AMG solver: temperature.
Can anybody give me hints on why it happens? I am using “ideal gas” as density and running the k-omega SST model.
Thank you for any suggestions given.

Kushal Puri · April 20, 2018, 07:41

Quote:

Originally Posted by Sprity Acharya

Hey everybody!
I have been working on gas flow through a pipe in Fluent. I vary the diameter of the pipe and compare the flow rates in this project. I was using air as the working material and got results. Now I switched to argon and fluent displays divergence detected in AMG solver: temperature.
Can anybody give me hints on why it happens? I am using “ideal gas” as density and running the k-omega SST model.
Thank you for any suggestions given.

What is your inlet boundary condition?
If it is velocity inlet try to run with mass flow inlet.

Sprity Acharya · April 20, 2018, 07:53

Hi!
I am using pressure inlet condition. It is a simulation of gas atomization process. I was able to get results till 4 mm of tube diameter. But i get divergence from 5 mm.
thanks.

LuckyTran · April 20, 2018, 12:34

Check your boundary conditions. If you're using a turbulence model then also make sure you update the turbulent length scale or hydraulic diameter at inlets.

Check also your initial conditions. Don't respond with "i used calculate from."

Sprity Acharya · April 20, 2018, 12:55

Quote:

Originally Posted by LuckyTran

Check your boundary conditions. If you're using a turbulence model then also make sure you update the turbulent length scale or hydraulic diameter at inlets.

Check also your initial conditions. Don't respond with "i used calculate from."

Hi! Thanks for replying. Will the turbulent length and hydraulic diameter vary with the gases used?
My boundary conditions are working perfectly for air. When switched to argon, Fluent gives me results for smaller diameter.

marauder · April 21, 2018, 02:59

What is the type of mesh you are using? Bad tets sometimes cause peaks and lows in temperature etc.

Try using constant density first, converge the flow then enable ideal gas density. Reducing relaxation factor for energy may also help.

April 20, 2018, 06:05	Divergence due to gas properties.	#1
Sprity Acharya New Member Sprity Acharya Join Date: Mar 2018 Posts: 3 Rep Power: 8	Hey everybody! I have been working on gas flow through a pipe in Fluent. I vary the diameter of the pipe and compare the flow rates in this project. I was using air as the working material and got results. Now I switched to argon and fluent displays divergence detected in AMG solver: temperature. Can anybody give me hints on why it happens? I am using “ideal gas” as density and running the k-omega SST model. Thank you for any suggestions given.

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April 20, 2018, 07:53		#3
Sprity Acharya New Member Sprity Acharya Join Date: Mar 2018 Posts: 3 Rep Power: 8	Hi! I am using pressure inlet condition. It is a simulation of gas atomization process. I was able to get results till 4 mm of tube diameter. But i get divergence from 5 mm. thanks.

April 20, 2018, 12:34		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,763 Rep Power: 66	Check your boundary conditions. If you're using a turbulence model then also make sure you update the turbulent length scale or hydraulic diameter at inlets. Check also your initial conditions. Don't respond with "i used calculate from."

April 21, 2018, 02:59		#6
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	What is the type of mesh you are using? Bad tets sometimes cause peaks and lows in temperature etc. Try using constant density first, converge the flow then enable ideal gas density. Reducing relaxation factor for energy may also help.