CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM Running, Solving & CFD

Spalart-Allmaras boundary condition

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

LinkBack Thread Tools Display Modes
Old   April 7, 2010, 17:04
Default Spalart-Allmaras boundary condition
Senior Member
Join Date: Feb 2010
Posts: 213
Rep Power: 8
vaina74 is on a distinguished road
I have a few questions about Spalart-Allmaras model, I applied it to an airfoil (blade section of a marine propeller).

1. I guess a turbulent viscosity ratio equal to 1, so nut = nu. I don't find a shared opinion about nuTilda: nuTilda = 3 * nu? nuTilda = 5 * nu? Maybe it's not so important.

2. Wich is the best range for y+?

3. My reference case is 2DAirfoil tutorial (incompressible/simpleFoam). I don't know the meaning of freestreamPressure or freestream BC types, I've used fieldValue or zeroGradient so far. Could you explain this to me? For istance, I used (k-w SST model):

inlet: p = zeroGradient;
U = uniform (7.30 0 0);
k = uniform 0.24;
omega = uniform 1.78

outlet: p = uniform 0;
U = zeroGradient;
k = zeroGradient;
omega = zeroGradient;

wall: p = zeroGradient;
U = uniform (0 0 0);
k = uniform 0.24; type: kqRWallFunction;
omega = uniform 1.78; type: kqRWallFunction;

side: p,U,k,omega = symmetryPlane;
frontAndBack: p,U,k,omega = empty;

Thanks for your help (and patience).
vaina74 is offline   Reply With Quote

Old   April 16, 2010, 08:17
Senior Member
Join Date: Feb 2010
Posts: 213
Rep Power: 8
vaina74 is on a distinguished road
I really don't understand. For external flows, FLUENT suggests \frac{\mu_t}{\mu}=1-10, ESI a range of 0.1-0.2, other sources about Spalart-Allamaras model suggest a 0.1 value... help me, please!

Last edited by vaina74; April 16, 2010 at 15:52.
vaina74 is offline   Reply With Quote

Old   April 3, 2013, 11:53
Join Date: Dec 2012
Location: Austin, USA
Posts: 52
Rep Power: 4
malaboss is on a distinguished road
Hi !
I really don't understand how to set the BC for the Spalart model either.
What I read in the litterature explains that it is suitable to choose something between 3*nu and 5*nu.

On the wiki, you can also find a formula which depends on the turbulent length scale and the turbulence intensity. When I apply it for a cylinder in a wind tunnel of turbulence intensity of 1%, a turbulence length scale of 0.11m (estimated with the dimensions of the wind tunnel used by Roschko), and for a velocity of 15 m/s, I have nutilda/nu >> 5

Conclusion 1: my flow, is not fully turbulent...
But lets make it more turbulent : we will have to increase velocity. But if we increase it, nutilda is going to increase, and never come closer to 5*nu

Conclusion 2 : there is something I don't understand on the way you choose the Spalart BC.

If anyone has an idea, I would be very delighted to hear it !
thanks in advance !
malaboss is offline   Reply With Quote


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
How exactly the "pressure outlet" bdry condition compute properties on the boundary? yating9901 FLUENT 3 June 28, 2010 12:26
Transient outlet boundary condition problem jwillie2000 CFX 1 December 7, 2009 18:07
Axis Boundary Condition..what is it? CFDtoy FLUENT 6 February 13, 2007 06:51
How to set boundary condition in Fluent for the fo Peiyong FLUENT 1 November 10, 2006 12:44
How to resolve boundary condition problem? sam FLUENT 2 July 20, 2003 02:19

All times are GMT -4. The time now is 02:37.