CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLOW-3D

Pipe flow - orifice plates

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 26, 2010, 08:06
Question Pipe flow - orifice plates
  #1
New Member
 
Alessandro
Join Date: Nov 2010
Posts: 2
Rep Power: 0
Alessandro P is on a distinguished road
Hi FLOW 3d users,

I recently started to approach to CFD. I would like to simulate the flow in a pipe with SINGLE-HOLE and MULTI-HOLE orifice plates, starting from experimental data (quite detailed and complete both for velocities and pressure measurements).
I am able to simulate a portion of the pipe working with polar coordinates and considering Z as the flow direction. I set pressure B.C. both at the inlet and the outlet of the pipe and an initial uniform velocity, but i tried also with velocity at the inlet and pressure at the outlet, with similar results. I activated a k-e turbulence model and a cavitation potential model.
The model converges and pressure and velocity fields are estimated well with respect to lab data.

The main problem is that I get the desired result modifying the parameter "ROUGHNESS" in surface properties. I found in the User's manual and in the forum that this parameter is proportional to the size of the roughness elements and has the dimensions of a length. Well, i am working with SI units and I have to use very high values of roughness in the model (0.08-0.1) to have a realistic simulation. Moreover, the model appears to work also because the distributed losses are much lower than the concentrated ones (due to the plate), while I would expect an opposite behavior in case of prevailing distributed losses.

Can anyone, please, explain this behavior? It is however correct?

Does anyone study the same problems?

Thank you for your attention,
Alessandro
Alessandro P is offline   Reply With Quote

Old   November 30, 2010, 00:42
Default
  #2
Senior Member
 
michael barkhudarov
Join Date: Mar 2009
Posts: 331
Rep Power: 9
MuxaB is on a distinguished road
Hi Alessandro,

I have a few questions to clarify.

Do you include both sides of the plate in the domain or is it adjacent to a mesh boundary? How big is the pipe?

Do I understand correctly that without using roughness, the flow losses are too small?
MuxaB is offline   Reply With Quote

Old   November 30, 2010, 04:55
Default
  #3
New Member
 
Alessandro
Join Date: Nov 2010
Posts: 2
Rep Power: 0
Alessandro P is on a distinguished road
Hi Michael,

thank you for your reply.

The pipe I am studying has a diameter D=200 mm. I am simulating complexively a length of 15D (7D upstream and 8D downstream...I know that it is not the best choice but I have limitations in the number of cells I can use, and I however verified the development of a correct velocity profile in the upstream and downstream sections). I am using only one mesh block, in cylindrical coordinates, that covers from 30 to 90 degrees on Y (according to the specific symmetry that I can find for different multihole orifices) from the beginning to the end of the pipe, so the plate is inside the domain. The rendering option showed that the software recognized correctly solid fractions and holes of the plate.

According to what I found in my simulations I think that you're right, so that reducing the roughness too much (also setting a zero value) I have small pressure losses, if compared to the concentrated ones I expect. On the contrary, setting a high value of roughness, I can get really good results.

Please, ask me for any other doubt,

Regards

Alessandro
Alessandro P is offline   Reply With Quote

Reply

Tags
orifice, pipe flow, pressure drop, roughness, turbulence

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
flow in perforated pipe distributor pertupd ANSYS 0 August 12, 2009 08:36
Reverse Flow at Rotating Pipe Outlet vismech STAR-CCM+ 1 August 11, 2009 10:38
About Turbulence Intensity (Pipe flow assimilated) gRomK13 Main CFD Forum 1 July 10, 2009 03:11
High speed compressible flow through pipe Munni Main CFD Forum 5 April 20, 2007 03:15
Turbulence in a pipe flow JM Main CFD Forum 4 December 21, 2006 05:04


All times are GMT -4. The time now is 13:14.