How do I specify a decrease in pressure?

Somebody · July 10, 2012, 07:45

I am trying to simulate a turbine in a pipe simply with a decrease in pressure - but I am unsure how to do this. Some help would be greatly appreciated.
Thank you.

ghorrocks · July 10, 2012, 19:22

You mean you want to replace a turbine with a pressure drop versus flow rate? This can be done with an interface or a source term. You can choose the best approach for your needs.

Somebody · July 11, 2012, 00:49

Thanks. Could you give me a few more details on how I can do that? I am quite a beginner with ANSYS software.

ghorrocks · July 11, 2012, 01:01

The easiest way is using an interface. Have a look at the tutorials for examples with interfaces.

You can add interface models which modify the flow through the interface. You could use a pressure change model and make it a function of mass flow rate to model the fan curve.

Alternately you can use source terms. This is a more advanced technique so best leave it until you have a bit more experience I suspect.

Somebody · July 12, 2012, 04:25

Thank you.
I've spent some time reading up on interfaces and working through a tutorial. I'm still a bit unsure about how they work, however. To create an interface, I first have to have separate domains, yes? Is there something I need to do in DesignModeler to be even able to create separate domains in CFX-Pre?

ghorrocks · July 12, 2012, 08:09

No, an interface can connect a single domain. In fact a single domain can be two separate meshed regions connected by an interface. You do not need two domains.

In designmodeller you need to make it different parts on both sides of the interface.

Somebody · July 13, 2012, 04:19

Thanks for the help.

I have attempted to create this interface, with Pressure Change of -0.5 [bar], but when I try to update the solution I get the following error messages:

CFX Solver Manager: "An error has occurred in cfx5solve: The ANSYS CFX solver has terminated without writing a results file. Command on host wts4 exited with return code 0."
ANSYS Workbench: "The CFX Solver for system (file name) did not produce a results file. Detailed information can be found in the output fil for the run, which can be viewed by selecting Display Monitors from the Solution Component. Cell A5"

Any ideas for other key things I could be missing or misunderstanding?

ghorrocks · July 13, 2012, 07:53

This is the workbench error message. It does not tell you much. You need to open the CFX output file and see the error message there, that will tell you why it bombed out.

Somebody · July 13, 2012, 09:20

That's what I figured - the actual error message seemed awfully long to post, though.

So first, in CFX-Pre, I had the following warning: "In Analysis 'Flow Analysis 1' - Solver Control: When defining Mass and Momentum for a domain interface, it is recommended that a convergence criteria is specified for the Domain Interface Target."
I imagine that this might be my issue (or at least, one of my issues), but I could not figure out what to do about it. Any advice here?

(And again, thank you so much.)

ghorrocks · July 14, 2012, 05:35

Until you post the actual error message we cannot help you.

Post the output file as an attachment to a post.

Somebody · July 23, 2012, 04:20

Thanks again. Here is the Out File from CFX Solver Manager.

ghorrocks · July 23, 2012, 08:02

The error message is quite clear. You have A GGI interface which does not have any intersection. If this was not intended you better fix your mesh to make sure things line up. If this is correct and the interface does not join at times then use the expert parameter as it says.

Somebody · July 23, 2012, 10:15

I cannot figure out where the error with the mesh is. It seems to me that all parts are connecting? How do I figure out where the problem is?

ghorrocks · July 23, 2012, 18:41

Load your mesh in CFD-Post. There should be a variable (can't remember its name) which also shows you the connected and unconnected parts of the GGI. You should see there the unconnected GGI.

Somebody · July 24, 2012, 03:23

But if the CFX Solver "did not produce a results file," I can't load the problematic mesh in CFD Post, can I? (I am assuming that what I see when I click on Results is from before I tried messing with pressure...)

ghorrocks · July 24, 2012, 03:32

You can load def and cfx (CFX-Pre setup files) in CFD-Post.

Also you should make a results file at time step zero which will output the initial condition.

Somebody · July 24, 2012, 04:06

Hmm. I still can't figure it out, and considering the time limit I now have (until the end of the week), I don't think I will be able to.

But thanks again for all your help. I otherwise would not have known how to even start. Do you have a favorite charity? I'd like to send a few dollars their way.

ghorrocks · July 24, 2012, 19:29

Very generous of you. I don't know of any charities like CFD addicts anonymous or anything like that

. As I suspect you are not in Australia none of the charities I support will be relevant to you so you will have to choose one yourself.

nicolas.sargi · May 20, 2022, 12:56

Hello. I am getting the same message.

In Analysis 'Flow Analysis 1' - Solver Control: When defining Mass and Momentum for a domain interface, it is recommended that a convergence criteria is specified for the Domain Interface Target.

Any idea on how to solve this?

Thank you

ghorrocks · May 21, 2022, 06:11

In CFX-Pre:
Solver control - Equation Class settings - turn continuity on and domain interface target will be at the bottom.

July 10, 2012, 07:45	How do I specify a decrease in pressure?	#1
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	I am trying to simulate a turbine in a pipe simply with a decrease in pressure - but I am unsure how to do this. Some help would be greatly appreciated. Thank you.

July 24, 2012, 04:06		#17
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	Hmm. I still can't figure it out, and considering the time limit I now have (until the end of the week), I don't think I will be able to. But thanks again for all your help. I otherwise would not have known how to even start. Do you have a favorite charity? I'd like to send a few dollars their way. Lance and karachun like this.

July 24, 2012, 19:29		#18
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	Very generous of you. I don't know of any charities like CFD addicts anonymous or anything like that . As I suspect you are not in Australia none of the charities I support will be relevant to you so you will have to choose one yourself. karachun likes this.

May 21, 2022, 06:11		#20
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	In CFX-Pre: Solver control - Equation Class settings - turn continuity on and domain interface target will be at the bottom. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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July 10, 2012, 19:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	You mean you want to replace a turbine with a pressure drop versus flow rate? This can be done with an interface or a source term. You can choose the best approach for your needs.

July 11, 2012, 00:49		#3
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	Thanks. Could you give me a few more details on how I can do that? I am quite a beginner with ANSYS software.

July 11, 2012, 01:01		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	The easiest way is using an interface. Have a look at the tutorials for examples with interfaces. You can add interface models which modify the flow through the interface. You could use a pressure change model and make it a function of mass flow rate to model the fan curve. Alternately you can use source terms. This is a more advanced technique so best leave it until you have a bit more experience I suspect.

July 12, 2012, 04:25		#5
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	Thank you. I've spent some time reading up on interfaces and working through a tutorial. I'm still a bit unsure about how they work, however. To create an interface, I first have to have separate domains, yes? Is there something I need to do in DesignModeler to be even able to create separate domains in CFX-Pre?

July 12, 2012, 08:09		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	No, an interface can connect a single domain. In fact a single domain can be two separate meshed regions connected by an interface. You do not need two domains. In designmodeller you need to make it different parts on both sides of the interface.

July 13, 2012, 04:19		#7
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	Thanks for the help. I have attempted to create this interface, with Pressure Change of -0.5 [bar], but when I try to update the solution I get the following error messages: CFX Solver Manager: "An error has occurred in cfx5solve: The ANSYS CFX solver has terminated without writing a results file. Command on host wts4 exited with return code 0." ANSYS Workbench: "The CFX Solver for system (file name) did not produce a results file. Detailed information can be found in the output fil for the run, which can be viewed by selecting Display Monitors from the Solution Component. Cell A5" Any ideas for other key things I could be missing or misunderstanding?

July 13, 2012, 07:53		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	This is the workbench error message. It does not tell you much. You need to open the CFX output file and see the error message there, that will tell you why it bombed out.

July 13, 2012, 09:20		#9
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	That's what I figured - the actual error message seemed awfully long to post, though. So first, in CFX-Pre, I had the following warning: "In Analysis 'Flow Analysis 1' - Solver Control: When defining Mass and Momentum for a domain interface, it is recommended that a convergence criteria is specified for the Domain Interface Target." I imagine that this might be my issue (or at least, one of my issues), but I could not figure out what to do about it. Any advice here? (And again, thank you so much.)

July 14, 2012, 05:35		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	Until you post the actual error message we cannot help you. Post the output file as an attachment to a post.

July 23, 2012, 08:02		#12
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	The error message is quite clear. You have A GGI interface which does not have any intersection. If this was not intended you better fix your mesh to make sure things line up. If this is correct and the interface does not join at times then use the expert parameter as it says.

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July 23, 2012, 10:15		#13
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	I cannot figure out where the error with the mesh is. It seems to me that all parts are connecting? How do I figure out where the problem is?

July 23, 2012, 18:41		#14
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	Load your mesh in CFD-Post. There should be a variable (can't remember its name) which also shows you the connected and unconnected parts of the GGI. You should see there the unconnected GGI.

July 24, 2012, 03:23		#15
Somebody New Member Join Date: Jun 2012 Posts: 10 Rep Power: 14	But if the CFX Solver "did not produce a results file," I can't load the problematic mesh in CFD Post, can I? (I am assuming that what I see when I click on Results is from before I tried messing with pressure...)

July 24, 2012, 03:32		#16
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,934 Rep Power: 145	You can load def and cfx (CFX-Pre setup files) in CFD-Post. Also you should make a results file at time step zero which will output the initial condition.

May 20, 2022, 12:56		#19
nicolas.sargi New Member Nicolas Sargi Join Date: May 2022 Posts: 7 Rep Power: 4	Hello. I am getting the same message. In Analysis 'Flow Analysis 1' - Solver Control: When defining Mass and Momentum for a domain interface, it is recommended that a convergence criteria is specified for the Domain Interface Target. Any idea on how to solve this? Thank you