CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

How do I specify a decrease in pressure?

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By Somebody

Reply
 
LinkBack Thread Tools Display Modes
Old   July 10, 2012, 07:45
Question How do I specify a decrease in pressure?
  #1
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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.
Somebody is offline   Reply With Quote

Old   July 10, 2012, 19:22
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 11, 2012, 00:49
Default
  #3
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
Thanks. Could you give me a few more details on how I can do that? I am quite a beginner with ANSYS software.
Somebody is offline   Reply With Quote

Old   July 11, 2012, 01:01
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 12, 2012, 04:25
Default
  #5
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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?
Somebody is offline   Reply With Quote

Old   July 12, 2012, 08:09
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 13, 2012, 04:19
Default
  #7
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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?
Somebody is offline   Reply With Quote

Old   July 13, 2012, 07:53
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 13, 2012, 09:20
Default
  #9
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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.)
Somebody is offline   Reply With Quote

Old   July 14, 2012, 05:35
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Until you post the actual error message we cannot help you.

Post the output file as an attachment to a post.
ghorrocks is offline   Reply With Quote

Old   July 23, 2012, 04:20
Default
  #11
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
Thanks again. Here is the Out File from CFX Solver Manager.
Attached Files
File Type: txt notsurehowtofixthis.txt (18.0 KB, 8 views)
Somebody is offline   Reply With Quote

Old   July 23, 2012, 08:02
Default
  #12
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 23, 2012, 10:15
Default
  #13
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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?
Somebody is offline   Reply With Quote

Old   July 23, 2012, 18:41
Default
  #14
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 24, 2012, 03:23
Default
  #15
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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...)
Somebody is offline   Reply With Quote

Old   July 24, 2012, 03:32
Default
  #16
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   July 24, 2012, 04:06
Default
  #17
New Member
 
Join Date: Jun 2012
Posts: 10
Rep Power: 5
Somebody is on a distinguished road
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 likes this.
Somebody is offline   Reply With Quote

Old   July 24, 2012, 19:29
Default
  #18
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,658
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 06:27
Setup/monitor points of pressure and force coefficients siw CFX 3 October 22, 2010 06:07
Operating condition in Fluent MASOUD FLUENT 3 September 16, 2010 17:50
Help ASAP! pressure inlet & outlet engahmed FLUENT 0 June 13, 2010 15:33
Setting pressure and velocity in inlet Asghari FLUENT 5 September 22, 2006 13:23


All times are GMT -4. The time now is 04:38.