|
[Sponsors] |
February 2, 2011, 17:18 |
first grid size and y-plus
|
#1 |
Senior Member
Morteza
Join Date: May 2010
Location: Iran,Islamic Republic of
Posts: 161
Rep Power: 15 |
hi
i am going to model a turbulent flow over a flat plate. if i want to extract a given y-plus, how can i set the first grid size? is there any formula to calculate the distance between wall and first grid in a given flow? thank you in advance |
|
February 2, 2011, 20:51 |
|
#2 |
Senior Member
Real Name :)
Join Date: Jan 2010
Location: United States
Posts: 192
Rep Power: 16 |
The first grid height can be set easily when you're first meshing the problem (Gambit, ANSYS Meshing, etc..). After the mesh has already been created, fluent has some adaptation routines for refining the mesh near walls/boundaries, assuming they've been named. Have a look through the manual: Adapting Grids
As far as the required spacing, have a look here:http://geolab.larc.nasa.gov/APPS/YPlus/ |
|
February 3, 2011, 02:59 |
|
#3 |
New Member
Amir
Join Date: Nov 2010
Location: Shiraz,Iran
Posts: 12
Rep Power: 15 |
Hi morteza,
note that y+ is a function of u*,nu and y. therefore you should compute average y+ on your plate. because u* varies along the plate , to obtain the same y+ over it , you ought to use non uniform grid that is not reasonable. I think a try and error procedure over averaged y+ using adaptation tools in FLUENT can be helpful. |
|
February 3, 2011, 09:22 |
|
#4 |
Senior Member
Join Date: Nov 2009
Posts: 411
Rep Power: 19 |
The y+ calculators are usually based on formulas for the flat plate. However you can successfully use them for curved surfaces (airfoils) using a bit of trial and error.
If you are interested in the underlying theory check: Anderson - Fundamentals of Aerodynamics |
|
February 4, 2011, 09:17 |
|
#5 | |
Senior Member
Morteza
Join Date: May 2010
Location: Iran,Islamic Republic of
Posts: 161
Rep Power: 15 |
Quote:
the calculator that you have sent its link for me , is for which turbulence model? |
||
February 4, 2011, 18:46 |
|
#6 |
Senior Member
Real Name :)
Join Date: Jan 2010
Location: United States
Posts: 192
Rep Power: 16 |
It's turbulence-model-independent.
Please see the following:http://www.cfd-online.com/Wiki/Dimen..._wall_distance |
|
February 4, 2011, 19:06 |
RE:first grid size and y-plus
|
#7 |
New Member
cfd_mistry_science
Join Date: Feb 2011
Posts: 2
Rep Power: 0 |
The y+ value is u*.y/nu, where y is the distance to the nearest wall. and this is your first grid size. u* you can take 1-5% of the bulk velocity and nu is the local kinematic viscosity and it depends upon the fluid is gas or liquid. But i take the same as the bulk fluid is in the computation. but it varies if flow is multiphase then nu will be different.
then if you want the y+ value 0.1 or less then this value then you can calculate the y value with above equation and this will be your first grid size. |
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
critical error during installation of openfoam | Fabio88 | OpenFOAM Installation | 21 | June 2, 2010 03:01 |
OF 1.6 | Ubuntu 9.10 (64bit) | GLIBCXX_3.4.11 not found | piprus | OpenFOAM Installation | 22 | February 25, 2010 13:43 |
Phase locked average in run time | panara | OpenFOAM | 2 | February 20, 2008 14:37 |
fluent add additional zones for the mesh file | SSL | FLUENT | 2 | January 26, 2008 11:55 |
Combustion Convergence problems | Art Stretton | Phoenics | 5 | April 2, 2002 05:59 |