# abou the Y Plus

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 January 22, 2007, 04:13 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

 January 22, 2007, 17:11 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

 January 22, 2007, 21:23 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

 January 23, 2007, 16:54 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

 January 23, 2007, 21:08 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

 January 23, 2007, 22:38 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

 January 24, 2007, 17:18 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

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

 January 26, 2007, 08:35 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 .

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post cognit OpenFOAM 24 October 28, 2014 02:33 sberg OpenFOAM Running, Solving & CFD 10 February 25, 2014 20:39 alberto OpenFOAM Running, Solving & CFD 73 November 10, 2008 18:58 sega OpenFOAM Native Meshers: blockMesh 9 May 24, 2008 06:15 soeren OpenFOAM Running, Solving & CFD 0 May 11, 2008 17:22

All times are GMT -4. The time now is 17:54.

 Contact Us - CFD Online - Top