×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

*
*
*
*

Thanks. We have received your request and will respond promptly.

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Flow rate in and out does not match

thread997-234505

Flow rate in and out does not match

Flow rate in and out does not match

(OP)
I recently reviewed a ANSYS CFD report of a custom valve and noticed that the flow rate in and flow rate out did not match. More came in then out.  

I am currently playing with the Comsol packages and did a quick model of a pipe with a reduced port in the middle.  Again the report showed a difference.  More flow in then out the back end.

(water used in both scenerios)

I am obviously new to this stuff so I am thinking there is something fundamental I am missing.

Any thoughts???
 

RE: Flow rate in and out does not match

Most likely either your solutions haven't converged, or you have a gap in your mesh.

RE: Flow rate in and out does not match

What Mint said.  Or, you have a third port in the model, that you didn't know about?

Plot residual errors vs. iteration number, see if solution is converging.

Plot streamlines, look for funky behavior (streamlines diving into the wall and disappearing).

Possibly there is a leak in the CPU memory, and all the water is going thru there, look for a puddle under your PC. :)

RE: Flow rate in and out does not match

gap in your mesh = third port in the model, that you didn't know about

Yes?

RE: Flow rate in and out does not match

Kinda - but "gap in mesh" in my mind meant "I built the model, but it's f'd up".  Third port = it's somebody else's model, of a valve type you are not familiar with (multi-port), and you didn't set the b.c.'s correctly.  Same effect, different root cause.

Sorry to poach on your reply Mint, I'll shut up now.

RE: Flow rate in and out does not match

(OP)
Thanks for the input.

I am positive that in both cases there is no third port. I've looked at every possible chart or graph and they look fairly correct. I also believe the mesh to be correct. I have even refined it with minimal change to the results.

I'll see if I can find the residual error information.

btrueblood - I keep towels under my pc just in case of such a leak.

 

RE: Flow rate in and out does not match

When you say that the flows don't match do you mean there is a signifigant difference? Or are we talking about a difference of say 1.50 GPM IN and 1.498895 OUT?

Typically with this sort of thing I see a very slight difference as described above when using COSMOS FloWorks. I don't consider the above example anything to fret about.

RE: Flow rate in and out does not match

(OP)
In the valve flow report the difference was about 10%
In my model its about 110%  The traces look fine so I am a little stumped.  I will provide updates once I return from my travels and have time to go over everything again.
 

RE: Flow rate in and out does not match

What is the size of your model ?  

RE: Flow rate in and out does not match

Have you accounted for losses?

Fe

RE: Flow rate in and out does not match

I've gone trough several problems that sounds the same as you have. And the troubles has always come from the boundary setting. Somehow, one or more nodes or edges on the mesh belongs to Neumann Bc's which should be Dirichlet Bc's.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now
Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close