CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

wall y-plus problem: unable to manage between 30 to 300..kindly help..

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 8, 2014, 02:18
Default wall y-plus problem: unable to manage between 30 to 300..kindly help..
  #1
New Member
 
maaz ahmad
Join Date: Dec 2011
Location: india
Posts: 21
Rep Power: 14
maaz is on a distinguished road
i am pasting the problem link here, below,,, images also attached here...


http://www.cfd-online.com/Forums/mai...-building.html
maaz is offline   Reply With Quote

Old   February 12, 2014, 10:54
Default
  #2
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 337
Rep Power: 15
Aeronautics El. K. is on a distinguished road
What turbulence model do you plan to use?
Are you going to use FLUENT (or CFX) for you analysis?

If so, Menter suggests to follow a y+=1 strategy and use a y+_insensitive turbulence model. I think that most of their models are like that now but take that with a pinch of salt as I'm not absolutely sure.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   February 13, 2014, 23:41
Default
  #3
New Member
 
maaz ahmad
Join Date: Dec 2011
Location: india
Posts: 21
Rep Power: 14
maaz is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
What turbulence model do you plan to use?
Are you going to use FLUENT (or CFX) for you analysis?

If so, Menter suggests to follow a y+=1 strategy and use a y+_insensitive turbulence model. I think that most of their models are like that now but take that with a pinch of salt as I'm not absolutely sure.
thanx for response....i am using fluent software...and solver is std k-epsilon..with std wall functions (not enhanced)...actually the problem starts when i once run problem....my values of pressure coeff. remain good but y plus falls below 30...as i alter the mesh of those places showing y plus less than 30, it starts showing absurd values of pressure coeff. ,,,so when i control the y plus, pressure coeff becomes absurd...this is the problem.....so i need help.....
maaz is offline   Reply With Quote

Old   February 14, 2014, 14:51
Default
  #4
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 337
Rep Power: 15
Aeronautics El. K. is on a distinguished road
Quote:
Originally Posted by maaz View Post
thanx for response....i am using fluent software...and solver is std k-epsilon..with std wall functions (not enhanced)...actually the problem starts when i once run problem....my values of pressure coeff. remain good but y plus falls below 30...as i alter the mesh of those places showing y plus less than 30, it starts showing absurd values of pressure coeff. ,,,so when i control the y plus, pressure coeff becomes absurd...this is the problem.....so i need help.....
Maybe your mesh is too coarse generally. If the mesh was good enough then you would get the Cp right and you wouldn't have the correct Cd. I would try to refine the mesh and go for y+=1 and use enhanced wall treatment.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   February 15, 2014, 00:13
Default
  #5
New Member
 
maaz ahmad
Join Date: Dec 2011
Location: india
Posts: 21
Rep Power: 14
maaz is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
Maybe your mesh is too coarse generally. If the mesh was good enough then you would get the Cp right and you wouldn't have the correct Cd. I would try to refine the mesh and go for y+=1 and use enhanced wall treatment.
actually when i refine the mesh to get values of y+=1, gambit crashes with the error: out of memory..so i cant take that much fine mesh..if you can suggest me anything for this ..please..
maaz is offline   Reply With Quote

Old   February 15, 2014, 21:05
Default
  #6
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK
Posts: 337
Rep Power: 15
Aeronautics El. K. is on a distinguished road
I don't know if there's going to make much difference but try y+<5 and enhanced wall treatment in Fluent. If you gambit crashes again, go again for y+>30 and standard wall functions.

However, I believe that you should refine your grid generally, not just near the walls.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   February 21, 2014, 05:41
Default
  #7
New Member
 
maaz ahmad
Join Date: Dec 2011
Location: india
Posts: 21
Rep Power: 14
maaz is on a distinguished road
my ske and rng values are showing much difference ...anyone can point out the reason...
maaz is offline   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
Natural convection in a closed domain STILL NEEDING help! Yr0gErG FLUENT 4 December 2, 2019 01:04
problem in using of additional variable in wall velocity adsladsl CFX 10 May 31, 2015 20:29
Heat Flux at wall in a conjugate heat transfer problem Chander CFX 2 July 9, 2011 23:22
Two Sided wall Problem Mk1987 ANSYS Meshing & Geometry 0 March 26, 2010 14:09
moving wall BC problem Sourabh Main CFD Forum 1 August 8, 2006 08:47


All times are GMT -4. The time now is 14:34.