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

abou the Y Plus

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 22, 2007, 04:13
Default abou the Y Plus
  #1
Eric
Guest
 
Posts: n/a
Dear Friends,

I am simulating the distribution of compressible air in cylinder. The value of Y plus should be between 30 and 100. But my result is between 10 and 148. How to do it? Could you give me some advice, thank you in advance.

Eric
  Reply With Quote

Old   January 22, 2007, 17:11
Default Re: abou the Y Plus
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

Why do you say y+ should be between 30 and 100? For many simulations y+ can higher than 100, and with automatic wall functions y+ can go down to less than one.

The standard way of adjusting y+ is by remeshing with a different thickness for the first inflation layer.

Glenn Horrocks
  Reply With Quote

Old   January 22, 2007, 21:23
Default Re: abou the Y Plus
  #3
eric
Guest
 
Posts: n/a
Dear Mr. Horrocks

Many thanks for your answer.

The person in Ansys (CFX) company told me that Y plus value.

As you said, I am trying the first layer thickness.

Best Regards Eric
  Reply With Quote

Old   January 23, 2007, 16:54
Default Re: abou the Y Plus
  #4
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

Whether that range is suitable or not depends on what you are simulating. In that range you will be using the wall function approach. You should do a mesh sensitivity check to see if your near wall spacing gives reliable results.

Glenn Horrocks
  Reply With Quote

Old   January 23, 2007, 21:08
Default Re: abou the Y Plus
  #5
Hong
Guest
 
Posts: n/a
Hello, Glenn

Could you please provide more information on mesh sensitivity check?

For example, should I keep the same Y+ value for different meshes ( which will be used for sentivity tests)

Regards,

Hong
  Reply With Quote

Old   January 23, 2007, 22:38
Default Re: abou the Y Plus
  #6
eric
Guest
 
Posts: n/a
Maybe Y plus is used for the mesh quality near the wall of the model.

So, Mr. Horrocks could you explain "a mesh sensitivity check to see if your near wall spacing gives reliable results." Thank you very much

Eric
  Reply With Quote

Old   January 24, 2007, 17:18
Default Re: abou the Y Plus
  #7
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

A mesh sensitivity check is where you run a number of different mesh sizes and check the results of important parameters. Assuming the simulation converges to the exact answer at zero mesh spacing, you then can estimate the error of your simulation by comparing to the finest mesh size. You then can select a mesh size which produces an acceptable level of error for your purposes.

A detailed analysis of mesh sensitivity analysis can be found in the textbook "Computational Fluid Dynamics" by Roache. Highly recommended reading for anyone interested in validating CFD results.

The Journal of Fluids Engineering demands all papers have minimum standards of validation and verification. Their policy is well worth a read: journaltool.asme.org/Templates/JFENumAccuracy.pdf

Glenn Horrocks
  Reply With Quote

Old   January 24, 2007, 23:28
Default Re: abou the Y Plus
  #8
Eric
Guest
 
Posts: n/a
Many thanks for Mr.Horrocks answer. Thank you very much.
  Reply With Quote

Old   January 26, 2007, 08:35
Default Re: abou the Y Plus
  #9
tarek
Guest
 
Posts: n/a
Hi Eric, I come cross ur qtion on line, Ive read the answers; I don't agree about that, because the first thing to talk about before look at the Y+, is which turbulence model you use?. Example standard K-E is not longer valid in internal flows, so your y+ doesn't mean any thing, and flowing ur setting , u are in compressible flow, ur y+ should be less than 3 units, no even 5. U need to do very fine mesh near the wall; then u can make a mesh adaptation in the region where ur solution on y+ is still very high .

  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Open Foam for ship hydrodynamics cognit OpenFOAM 27 March 14, 2021 17:54
TwoPhaseEulerFoam convergence problems alberto OpenFOAM Running, Solving & CFD 74 June 7, 2016 06:26
Problems with the RSM in simpleFoam sberg OpenFOAM Running, Solving & CFD 10 February 25, 2014 20:39
[blockMesh] I thought about this solution to create a spherical mesh. sega OpenFOAM Meshing & Mesh Conversion 9 May 24, 2008 07:15
Variable inletoutlet for dynamic mesh mixer2D case soeren OpenFOAM Running, Solving & CFD 0 May 11, 2008 18:22


All times are GMT -4. The time now is 01:14.