Simulation of a emptying gas cylinder

ticofiz · March 3, 2016, 19:59

Hi everybody,

I want to simulate a gas cylinder that that is open and closed periodically but I have problems with defining the Boundary Conditions. I do not know how to define the interior of the cylinder as there is no inlet. How can I specify that the interior is a gas at certain pressure? Also is there any way I could put a periodic opening and closing of the outlet?

Many thanks

Ahmed Saeed Mansour · March 4, 2016, 00:13

Check the tutorials out....I am sorry I cannot help you with more information.
https://www.google.com.eg/?gfe_rd=cr...cylinder+ansys

ticofiz · March 4, 2016, 05:34

Quote:

Originally Posted by Ahmed Saeed Mansour

Check the tutorials out....I am sorry I cannot help you with more information.
https://www.google.com.eg/?gfe_rd=cr...cylinder+ansys

I think that most of the people are using today google search. I have tried many tutorials before asking here but none of them gave me any idea on how to solve this problem. I hoped that some of the forum users had encountered the same problem and could give some useful tips.

LuckyTran · March 6, 2016, 00:49

I'm not quite sure what your problem is. Your interior and inlets/outlets should have been done already after you meshed the geometry. Do you even have your geometry defined? How about a mesh?

The interior is independent of any boundaries (inlet and outlets). The fact that there is no inlet has no effect whatsoever on the interior.

There's several ways to model a periodically open and closed valve but it depends on what the user is trying to do. If you can define precisely how you want to model the action of the valve opening then maybe someone can then help you with the implementation. Valve opening and close is too vague. Does it close instantaneously? Does it close completely or can it leak? What does the valve actually do? How do you want your valve to behave?

Once you have clearly started your problem, it is fairly straightforward. Unfortunately, Fluent is not the place for you to still be brainstorming.

ticofiz · March 6, 2016, 01:54

Thank you for your reply,

The problem is that, after importing the mesh in Fluent I do not know how to define the interior of the cylinder as being a gas with a certain pressure. All the simulations I have done so far had inlet and outlet so the boundary conditions were easy to define.
In my case I want to see in time how the gas density profile changes inside the cylinder when I open or close suddenly the outlet. I could define the outlet as "pressure outlet" but how can I feed the gas when there is no inlet?

The valve can be idealised as a instant open or close.

LuckyTran · March 6, 2016, 10:41

It is a closed cylinder so you do not need any inlets.

What you have is a transient problem. Therefore you need to specify the initial pressure of the contents via the initialization.

Use a pressure outlet for when your valve is open. When the valve is closed, change it from a pressure outlet to a wall (no-slip or slip wall). You can do this manually or automate it.

ticofiz · March 6, 2016, 20:24

Quote:

Originally Posted by LuckyTran

It is a closed cylinder so you do not need any inlets.

What you have is a transient problem. Therefore you need to specify the initial pressure of the contents via the initialization.

Use a pressure outlet for when your valve is open. When the valve is closed, change it from a pressure outlet to a wall (no-slip or slip wall). You can do this manually or automate it.

It worked perfectly. Thank you very much for your help.

ticofiz · March 6, 2016, 23:30

I have added two extra zones, as shown in the attached picture. If I do not bother too much could you please tell me how I can specify that the gas flows only from the middle zone? I have no option in the Initialization to choose any of those zones. I have defined the outer shell of the added zones as pressure outlet and the outer shell of the middle zone as wall. The interface between zones is defined as interior.

ticofiz · March 7, 2016, 01:46

--------------------------------------------

LuckyTran · March 7, 2016, 07:54

You can patch variables in individual zones if that's what you're asking about.

ticofiz · March 7, 2016, 19:00

Quote:

Originally Posted by LuckyTran

You can patch variables in individual zones if that's what you're asking about.

Yes, it is exactly what I was looking for.
Thank you for your help.

March 3, 2016, 19:59	Simulation of a emptying gas cylinder	#1
ticofiz New Member Alexander Comsa Join Date: Jan 2016 Posts: 15 Rep Power: 10	Hi everybody, I want to simulate a gas cylinder that that is open and closed periodically but I have problems with defining the Boundary Conditions. I do not know how to define the interior of the cylinder as there is no inlet. How can I specify that the interior is a gas at certain pressure? Also is there any way I could put a periodic opening and closing of the outlet? Many thanks

March 6, 2016, 10:41		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	It is a closed cylinder so you do not need any inlets. What you have is a transient problem. Therefore you need to specify the initial pressure of the contents via the initialization. Use a pressure outlet for when your valve is open. When the valve is closed, change it from a pressure outlet to a wall (no-slip or slip wall). You can do this manually or automate it. ticofiz likes this.

March 7, 2016, 01:46		#9
ticofiz New Member Alexander Comsa Join Date: Jan 2016 Posts: 15 Rep Power: 10	-------------------------------------------- Last edited by ticofiz; March 7, 2016 at 02:32. Reason: I put a question without checking properly my simulation.

March 7, 2016, 07:54		#10
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	You can patch variables in individual zones if that's what you're asking about. ticofiz likes this.

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March 4, 2016, 00:13		#2
Ahmed Saeed Mansour Senior Member Have a nice time! Join Date: Feb 2016 Location: mech.eng.ahmedmansour@gmail.com Posts: 291 Rep Power: 11	Check the tutorials out....I am sorry I cannot help you with more information. https://www.google.com.eg/?gfe_rd=cr...cylinder+ansys

March 6, 2016, 00:49		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	I'm not quite sure what your problem is. Your interior and inlets/outlets should have been done already after you meshed the geometry. Do you even have your geometry defined? How about a mesh? The interior is independent of any boundaries (inlet and outlets). The fact that there is no inlet has no effect whatsoever on the interior. There's several ways to model a periodically open and closed valve but it depends on what the user is trying to do. If you can define precisely how you want to model the action of the valve opening then maybe someone can then help you with the implementation. Valve opening and close is too vague. Does it close instantaneously? Does it close completely or can it leak? What does the valve actually do? How do you want your valve to behave? Once you have clearly started your problem, it is fairly straightforward. Unfortunately, Fluent is not the place for you to still be brainstorming.

March 6, 2016, 01:54		#5
ticofiz New Member Alexander Comsa Join Date: Jan 2016 Posts: 15 Rep Power: 10	Thank you for your reply, The problem is that, after importing the mesh in Fluent I do not know how to define the interior of the cylinder as being a gas with a certain pressure. All the simulations I have done so far had inlet and outlet so the boundary conditions were easy to define. In my case I want to see in time how the gas density profile changes inside the cylinder when I open or close suddenly the outlet. I could define the outlet as "pressure outlet" but how can I feed the gas when there is no inlet? The valve can be idealised as a instant open or close.