How to define the conditional open state for domain interface

sakalido · April 9, 2014, 14:26

Hello,

I am modeling a tank filled with air and water (two phase flow) with two openings in the bottom of the tank. one opening opens to a channel filled with air and the other opening opens to a channel filled with water.
tank and each channels are separate domains. So I have three domains totally.

I have fluid fluid interface at the opening, one of them is the default interface. The other one is made manually.

I want to be able to control the time of opening and closing of these openings. Meaning that I want to for example leave the opening to water channel open for 1 second and then close it for 1 second. I think I should use "conditional connection control", correct?
But the problem is although I can control the water discharge from the opening to air channel by defining my "conditional connection control" as "conditional open state" of "Time>1[s]", I cannot control the water discharge from the water opening bu using the same setting. No matter I use "conditional connections control" or I don't use it, no water is discharged from this opening as if it is a wall boundary condition. Although it is exactly defined as the other opening. What am I missing here?
I am attaching a picture.

Thank you,
Sara

ghorrocks · April 9, 2014, 20:11

I am a little confused by your question.

Conditional openings are on interfaces, not openings. And what do you mean by "no water is discharged from this opening as if it is a wall boundary condition"? Flow does not go through wall boundaries so what do you mean?

Can you clarify whether you are talking about the conditional opening settings on the interfaces, or the opening boundary conditions at the end of your ducts.

sakalido · April 10, 2014, 10:28

hello Glen ,

I'm sorry I was not clear. I'll try to describe better.

I am talking about interfaces.
I am trying to define two "conditional open state" to discharge water from the tank through two channels. One channel filled with air and the other filled with water.

I can control opening and closing of the interface connected to the channel filled with air but I cannot do the same for the interface connected to the channel filled with water. In other words, water does not pass through the interface. Although I set the conditional open state to have an open interface to be able to let water discharge from the tank through the interface to the channel, but water does not pass through this interface.

I have no problem with the other interface which connects the tank to the air channel.

ghorrocks · April 10, 2014, 18:18

Can you post your CCL?

sakalido · May 1, 2014, 16:09

Hi all,

This problem is solved.
It was much simpler and more basic than what I was thinking.
The problem I had was I was not seeing water passing through the interface that was connecting the tank to the channel filled with water.

The problem was, in another downstream location, I had to define an interface between two domains. I had two domains without defining an interface between them. Therefore, the surface between these two interfaces acted like a wall.

Once I defined an interface between all my domains through which I wanted to pass water, the problem was solved.

Best,
Sara

Vaaj · April 27, 2017, 17:42

I have a problem in simulating compressed air flow from one container to another container connected through a tube.

At the end of the container which has compressed air at 21 bar(a) pressure there is a valve. It is open for 45 milliseconds and closed after that time.

I could not find help to simulate this on/off valve. I am not worried about the valve motion but the flow has to stop after 45ms.

I tried to simplify the approach by giving mass flow inlet without the compressed air container through the pipe, but the actual physics could not be captured as there are many assumptions to get the mass flow.

How to stop the flow from the pressurized container after 45 ms?

ghorrocks · April 27, 2017, 18:18

First of all: Please do not PM me with copies of posts on the forum. I do not answer CFD questions by PM.

You can do this by many methods:
* You can use the conditional opening on interfaces
* You could close a transient rotor stator interface
* You could put a region in as the valve and use a function to make the velocity in this region zero
* You could model the actual valve mechanism as it shuts.

Vaaj · April 27, 2017, 18:59

Thank you for your reply Glenn. Sorry for PMing with the question.

I am modeling the flow in ANSYS Fluent.
1) I am not aware of how to create conditional opening on interface. Are there any links to that effect?
2) Any link on how to do that will be helpful, as I am a chemical engineer and new to the designing and meshing I am in the learning phase
3) I do not know the velocity as the flow is choked for some time and unchoked thereafter. I want Fluent to let me know the property changes
4) I can see some help on creating check valve through dynamic meshing, but that is going to disturb the flow as the turbulence created in this flow is important and any obstruction created during the flow costs me. In case of check valve it is still going to be present in angle to the flow, are there any way in creating On/OFF valve like inserting a stop plate during the simulation? (I am being naive, but I have to ask questions to find answers, pardon me)

ghorrocks · April 27, 2017, 23:20

If you are using Fluent then my comments do not apply as they were for CFX. Try the Fluent forum.

Vaaj · May 2, 2017, 10:53

Hi Glenn,

In the simulation there is not outlet and I know the mass flow inlet (which varies with time), pressure (which varies with time), Temp and density varies with varying pressure (isentropic).

I am confused with setting the inlet boundary conditions.

If I set mass flow rate the velocity that I am calculating with hand is not matching with that of fluent (way too less). There is some problem with the gauge pressure/sonic pressure that determines the initial density that is making the difference.

How do you initialize compressible transient flow simulation in closed domain with one inlet and no outlet?

ghorrocks · May 2, 2017, 18:36

If you are using Fluent then my comments do not apply as they were for CFX. Try the Fluent forum.

Vaaj · May 2, 2017, 18:52

The concepts are same right. Can you give me some pointers? I am also going to try it in CFX.

ghorrocks · May 3, 2017, 08:42

These are pretty basic questions - have you done the tutorial examples from the ANSYS customer website? That answers basic questions like this.

April 10, 2014, 10:28	conditional open state for interface	#3
sakalido Member Sara S. Join Date: May 2010 Location: NJ, USA Posts: 41 Rep Power: 15	hello Glen , I'm sorry I was not clear. I'll try to describe better. I am talking about interfaces. I am trying to define two "conditional open state" to discharge water from the tank through two channels. One channel filled with air and the other filled with water. I can control opening and closing of the interface connected to the channel filled with air but I cannot do the same for the interface connected to the channel filled with water. In other words, water does not pass through the interface. Although I set the conditional open state to have an open interface to be able to let water discharge from the tank through the interface to the channel, but water does not pass through this interface. I have no problem with the other interface which connects the tank to the air channel.

May 1, 2014, 16:09	define an interface between all connected domains	#5
sakalido Member Sara S. Join Date: May 2010 Location: NJ, USA Posts: 41 Rep Power: 15	Hi all, This problem is solved. It was much simpler and more basic than what I was thinking. The problem I had was I was not seeing water passing through the interface that was connecting the tank to the channel filled with water. The problem was, in another downstream location, I had to define an interface between two domains. I had two domains without defining an interface between them. Therefore, the surface between these two interfaces acted like a wall. Once I defined an interface between all my domains through which I wanted to pass water, the problem was solved. Best, Sara

April 27, 2017, 17:42	transient flow with valve	#6
Vaaj New Member Bharatvaaj Join Date: Feb 2017 Posts: 23 Rep Power: 9	I have a problem in simulating compressed air flow from one container to another container connected through a tube. At the end of the container which has compressed air at 21 bar(a) pressure there is a valve. It is open for 45 milliseconds and closed after that time. I could not find help to simulate this on/off valve. I am not worried about the valve motion but the flow has to stop after 45ms. I tried to simplify the approach by giving mass flow inlet without the compressed air container through the pipe, but the actual physics could not be captured as there are many assumptions to get the mass flow. How to stop the flow from the pressurized container after 45 ms?

May 2, 2017, 10:53	Closed domain simulation	#10
Vaaj New Member Bharatvaaj Join Date: Feb 2017 Posts: 23 Rep Power: 9	Hi Glenn, In the simulation there is not outlet and I know the mass flow inlet (which varies with time), pressure (which varies with time), Temp and density varies with varying pressure (isentropic). I am confused with setting the inlet boundary conditions. If I set mass flow rate the velocity that I am calculating with hand is not matching with that of fluent (way too less). There is some problem with the gauge pressure/sonic pressure that determines the initial density that is making the difference. How do you initialize compressible transient flow simulation in closed domain with one inlet and no outlet?

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April 9, 2014, 20:11		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I am a little confused by your question. Conditional openings are on interfaces, not openings. And what do you mean by "no water is discharged from this opening as if it is a wall boundary condition"? Flow does not go through wall boundaries so what do you mean? Can you clarify whether you are talking about the conditional opening settings on the interfaces, or the opening boundary conditions at the end of your ducts.

April 10, 2014, 18:18		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can you post your CCL?

April 27, 2017, 18:18		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	First of all: Please do not PM me with copies of posts on the forum. I do not answer CFD questions by PM. You can do this by many methods: * You can use the conditional opening on interfaces * You could close a transient rotor stator interface * You could put a region in as the valve and use a function to make the velocity in this region zero * You could model the actual valve mechanism as it shuts.

April 27, 2017, 18:59		#8
Vaaj New Member Bharatvaaj Join Date: Feb 2017 Posts: 23 Rep Power: 9	Thank you for your reply Glenn. Sorry for PMing with the question. I am modeling the flow in ANSYS Fluent. 1) I am not aware of how to create conditional opening on interface. Are there any links to that effect? 2) Any link on how to do that will be helpful, as I am a chemical engineer and new to the designing and meshing I am in the learning phase 3) I do not know the velocity as the flow is choked for some time and unchoked thereafter. I want Fluent to let me know the property changes 4) I can see some help on creating check valve through dynamic meshing, but that is going to disturb the flow as the turbulence created in this flow is important and any obstruction created during the flow costs me. In case of check valve it is still going to be present in angle to the flow, are there any way in creating On/OFF valve like inserting a stop plate during the simulation? (I am being naive, but I have to ask questions to find answers, pardon me)

April 27, 2017, 23:20		#9
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you are using Fluent then my comments do not apply as they were for CFX. Try the Fluent forum.

May 2, 2017, 18:36		#11
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you are using Fluent then my comments do not apply as they were for CFX. Try the Fluent forum.

May 2, 2017, 18:52		#12
Vaaj New Member Bharatvaaj Join Date: Feb 2017 Posts: 23 Rep Power: 9	The concepts are same right. Can you give me some pointers? I am also going to try it in CFX.

May 3, 2017, 08:42		#13
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	These are pretty basic questions - have you done the tutorial examples from the ANSYS customer website? That answers basic questions like this.