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

Pipe Pressure Loss

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 15, 2009, 04:21
Default Pipe Pressure Loss
  #1
New Member
 
Antonio Caimano
Join Date: Mar 2009
Posts: 4
Rep Power: 8
PoliPro is on a distinguished road
Hi,

I simulated a simple incompressible air flow through a small pipe (diameter = 1 mm) with StarCCM+ in order to verify the pressure losses along it.
The values of pressure loss I obtained are quite higher (60%) than the analytical ones.
The mesh is good and the turbulence model I used is the k-epsilon.
Any suggestions?
PoliPro is offline   Reply With Quote

Old   May 15, 2009, 04:46
Default
  #2
SKK
Member
 
Join Date: Mar 2009
Posts: 55
Rep Power: 8
SKK is on a distinguished road
What is the Reynolds number of your flow? Is it turbulent or laminar?
SKK is offline   Reply With Quote

Old   May 15, 2009, 07:38
Default
  #3
New Member
 
Antonio Caimano
Join Date: Mar 2009
Posts: 4
Rep Power: 8
PoliPro is on a distinguished road
We can consider a Reynolds number of 600, so the flow is laminar.
I've already simulate that case with laminar model but result doesn't change.
I'd prefer to use turbulent model in order to validate it for the next application with sharp geometry variations.
PoliPro is offline   Reply With Quote

Old   May 15, 2009, 07:54
Default
  #4
SKK
Member
 
Join Date: Mar 2009
Posts: 55
Rep Power: 8
SKK is on a distinguished road
Are you using high or low Reynolds number turbulence model? What is your y+ values? In laminar case, how does the profile compare with Blasius's profile?

All failing, I would recheck the analytical solution to see if radius and diameter got extra 1/2 somewhere. This is a very common mistake and with 60% difference this is a very probable cause.

Last edited by SKK; May 15, 2009 at 08:15.
SKK is offline   Reply With Quote

Old   May 18, 2009, 09:42
Default
  #5
Senior Member
 
Aroon
Join Date: Apr 2009
Location: Racine WI
Posts: 148
Rep Power: 8
vishyaroon is on a distinguished road
I'm not surprised. One of my co-workers was trying something very basic like this (not sure whether it was pressure drop or laminar Nu values) and he could not get it to match analytical values.

Adapco should post some simple validations like this either in their web-page or the tutorials.
vishyaroon is offline   Reply With Quote

Old   May 20, 2009, 08:52
Default
  #6
New Member
 
Antonio Caimano
Join Date: Mar 2009
Posts: 4
Rep Power: 8
PoliPro is on a distinguished road
I am using an high Reynolds model.
Wall y+ is unfortunately < 15 and I know that it should be between 30 and 150.
I have not yet compared the profile I obtained with the Basius one, I will do...
No diameter/radius errors.

Next step is to change the turbulence model from k-epsilon to k-omega.
I could also try with a 2D model, in order to accelerate the process, what do you think?
PoliPro is offline   Reply With Quote

Old   May 20, 2009, 10:02
Default
  #7
SKK
Member
 
Join Date: Mar 2009
Posts: 55
Rep Power: 8
SKK is on a distinguished road
When you say you have tested Laminar model and the results do not change, do you mean the pressure drop does not change? That does not sound right.

Performance of turbulence models vary for different geometry depending on which model you are using. For example, Launder-Sharma model is one of the best model for a flat plate boundary layer simulation. This is mainly because the constants and formulation for each models are derived and validated against different kind of flows.

Test with increasing y+ and see if that helps. Both the production and dissipation terms are very large in the log law region of 30<y+<100. The low y+ may result in high shear stress you are getting as du/dy would be much larger. Having said that, generally skin friction results when simulated are not much better than 30% off the analytical solution.

k-w models are much better in modeling adverse pressure gradient situations. It might be a good idea to test these, especially since you are using turbulence to model laminar flow.

It might be a good idea to test a simple model, ie a flat plate model to validate the turbulence models.
SKK 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
Discrepancy between the measurements (pressure drop; VOF) blackemperor FLUENT 1 August 30, 2011 00:45
Pressure loss in PEM cell with different profiles rodrigoscf FloEFD, FloWorks & FloTHERM 1 April 14, 2009 10:00
Pressure Drop - Please Help - Simple Pipe Flow Joe A. FLUENT 2 April 23, 2007 07:50
Gas pressure question Dan Moskal Main CFD Forum 0 October 24, 2002 22:02
total pressure change in a pipe flow Im FLUENT 4 February 6, 2002 20:09


All times are GMT -4. The time now is 16:29.