Transient mass flow inlet profile.

jaewonlee · August 23, 2016, 08:28

Hi all.
Firstly, I am new in CFD, FLUENT.
When I use fluent, I put some input parameters, for example, 0.001kg/s. After finishing simulation, the results show hydrogen kept leaking whole simulation time(100s).
But I want to simulate only 10 second hydrogen leak, not all time period. After 10s, I just want to see how hydrogen disperse.
While i am trying to figure it out, I found that I need to make UDF file to simulate 10s leak.

Can someone help me to resolve my problem?

Thank you.

cturutoglu · August 23, 2016, 08:36

You dont need any udf. Calculate your case 10 seconds at first with hydrogen leaking and than stop the simulation, turn the mass-flow-inlet boundary to the Wall and run your calculation again up to 100s.

jaewonlee · August 24, 2016, 21:55

Thank you cturutoglu.

As you said, I carried out what you comment for me; simulating 10s leak, and then set the inlet to wall as boundary condition. Additionally, I tried to set the inlet quantity as 0 after 10s.

Unfortunately, I could not get the result that I expected. I thought after stopped leaking, hydrogen spread quickly. But the results did not show it. It just stay the position near inlet.

Can you let me know how to resolve this problem?

** My conditions are below.
- Model : Eulerian
- Viscous : k-e, realized
- inlet : Q(air)=0, Q(H2)=1.489e-06, pressure=50 Pa
- no outlet(confined geometry)

cturutoglu · August 26, 2016, 07:28

Firstly, you have to explain your solver settings in detail. Are you using VOF model? If yes, did you activate the gravity?. If no, which is a big physics fault, you need to set the Volume of Fluid (Vof) model. You can learn how vof works in tutorials.

You're welcome!

jaewonlee · August 28, 2016, 21:28

Thank you for your very kindness.
As you said, my setting is not VOF, but Eulerian, because my simulation deals with hydrogen dispersion in air. And I heard VOF model is not proper for gas & gas. And I activate the gravity of course.

Is my setting, Eulerian, big mistake? Do I have to choose VOF model as valid method?

cturutoglu · August 29, 2016, 05:36

No need to change your model you can go on eulerian. Did you patch the air to the all domain before simulation?

jaewonlee · August 29, 2016, 07:29

Sure, I added hydrogen as phase 2 in the setting.
At the very beginning of the result, 0 second(before hydrogen leaks), there are full of the air in the geometry.

Even though I don't know how to upload my picture file here, my figure shows that volume fraction of phase 1(air) is 1.

I really appreciate your reply.

August 23, 2016, 08:28	Transient mass flow inlet profile.	#1
jaewonlee New Member jaewon lee Join Date: Jun 2016 Posts: 5 Rep Power: 9	Hi all. Firstly, I am new in CFD, FLUENT. When I use fluent, I put some input parameters, for example, 0.001kg/s. After finishing simulation, the results show hydrogen kept leaking whole simulation time(100s). But I want to simulate only 10 second hydrogen leak, not all time period. After 10s, I just want to see how hydrogen disperse. While i am trying to figure it out, I found that I need to make UDF file to simulate 10s leak. Can someone help me to resolve my problem? Thank you.

August 23, 2016, 08:36		#2
cturutoglu Member CT Join Date: May 2016 Location: Turkey Posts: 32 Rep Power: 9	You dont need any udf. Calculate your case 10 seconds at first with hydrogen leaking and than stop the simulation, turn the mass-flow-inlet boundary to the Wall and run your calculation again up to 100s. jaewonlee likes this.

August 26, 2016, 07:28		#4
cturutoglu Member CT Join Date: May 2016 Location: Turkey Posts: 32 Rep Power: 9	Firstly, you have to explain your solver settings in detail. Are you using VOF model? If yes, did you activate the gravity?. If no, which is a big physics fault, you need to set the Volume of Fluid (Vof) model. You can learn how vof works in tutorials. You're welcome! jaewonlee likes this. Last edited by cturutoglu; August 26, 2016 at 07:29. Reason: forgot to thank

August 29, 2016, 05:36		#6
cturutoglu Member CT Join Date: May 2016 Location: Turkey Posts: 32 Rep Power: 9	No need to change your model you can go on eulerian. Did you patch the air to the all domain before simulation? jaewonlee likes this.

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August 24, 2016, 21:55		#3
jaewonlee New Member jaewon lee Join Date: Jun 2016 Posts: 5 Rep Power: 9	Thank you cturutoglu. As you said, I carried out what you comment for me; simulating 10s leak, and then set the inlet to wall as boundary condition. Additionally, I tried to set the inlet quantity as 0 after 10s. Unfortunately, I could not get the result that I expected. I thought after stopped leaking, hydrogen spread quickly. But the results did not show it. It just stay the position near inlet. Can you let me know how to resolve this problem? ** My conditions are below. - Model : Eulerian - Viscous : k-e, realized - inlet : Q(air)=0, Q(H2)=1.489e-06, pressure=50 Pa - no outlet(confined geometry)

August 28, 2016, 21:28		#5
jaewonlee New Member jaewon lee Join Date: Jun 2016 Posts: 5 Rep Power: 9	Thank you for your very kindness. As you said, my setting is not VOF, but Eulerian, because my simulation deals with hydrogen dispersion in air. And I heard VOF model is not proper for gas & gas. And I activate the gravity of course. Is my setting, Eulerian, big mistake? Do I have to choose VOF model as valid method?

August 29, 2016, 07:29		#7
jaewonlee New Member jaewon lee Join Date: Jun 2016 Posts: 5 Rep Power: 9	Sure, I added hydrogen as phase 2 in the setting. At the very beginning of the result, 0 second(before hydrogen leaks), there are full of the air in the geometry. Even though I don't know how to upload my picture file here, my figure shows that volume fraction of phase 1(air) is 1. I really appreciate your reply.