CFD Online URL
[Sponsors]
Home > Forums > FLUENT

Y+ and accuracy of Pressure Coefficient of a wing

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 3, 2005, 20:30
Default Y+ and accuracy of Pressure Coefficient of a wing
  #1
Mick
Guest
 
Posts: n/a
Hi All,

Forgot to ask a question in my previous thread.

The 2D analysis I am doing here has a Y+ value of 2 (min) and 11 (max), however the S-A Turbulence model says that a Y+ of 30 should be used.

Does it mean that the pressure coeff. are not right! or should I stick with the current value. The adapt option in Fluent doesnt seem to coarse the grid for Y+ of 30.

Thanks in advance,

Mick
  Reply With Quote

Old   October 4, 2005, 10:15
Default Re: Y+ and accuracy of Pressure Coefficient of a w
  #2
Razvan
Guest
 
Posts: n/a
Spallart-Almaras model is much better suited for y+=1. So adapt your mesh to this value. A value of y+=5-6 is very wrong (and I bet that's the medium value for your model)!

Observation: if you got a structured mesh, then coarsening is impossible (this is available only for unstructured meshes)!!

Razvan
  Reply With Quote

Old   October 4, 2005, 17:19
Default Re: Y+ and accuracy of Pressure Coefficient of a w
  #3
Mick
Guest
 
Posts: n/a
Hello Razwan,

Many Thanks for the reply. Yes you are right, I am using a structured grid close to the wing.

According to your advice I adapted the mesh to Y+=1 by using min value=1 and max value=1. Correct me if I did it the wrong way. Now, when I plot the turbulence for wall Y+, I dont see any lines that are close to 1. It is in a region of about 5 and 12!

What have I done wrong here?

Many Thanks in advance.

Mick
  Reply With Quote

Old   October 4, 2005, 17:39
Default Re: Y+ and accuracy of Pressure Coefficient of a w
  #4
Razvan
Guest
 
Posts: n/a
Use y+= (min(0.8),max(1.2)). It will not work otherway. Also, activate dinamic adaption, and set 10-20 iterations for adaption. This tehnique (adaption) is not so great after all, because it introduces a high gradient of cell volume right where it isn't needed: in the boundary layer! So, for better precision I use this type of adaption only in desperate cases. What you should try to do is to obtain a good grid right from the start. To do this, follow my instructions:

- make first a 2d grid for a flat plate, and calculate flow over this plate with BC for your final case (same velocity, temperature, pressure, etc)

- plot y+ values on the plate: this way you will find out if you have chosen the right size for first cell at the wall; if you did not succeed at the first shot, try again until you figure out what cell size would be needed to obtain a desired y+ value

- take this value and make a good grid for your final geometry.

Best wishes, Razvan
  Reply With Quote

Reply

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
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 07:27
Increasing the accuracy of pressure head values in output data Saeed1390 FLUENT 0 June 13, 2011 03:17
Finite Wing Simulation Altocirrus STAR-CCM+ 1 February 7, 2011 13:41
Intake Flow Simulation Accuracy atlantis83 FLUENT 0 April 25, 2010 06:18
negative static pressure !?! Marat Hoshim Main CFD Forum 15 October 26, 2000 12:48


All times are GMT -4. The time now is 09:49.