CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

k-omega-SST model (OF 1.6) - turbulent flat plate

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

Like Tree5Likes

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 5, 2011, 02:41
Default
  #21
Senior Member
 
Travis Carrigan
Join Date: Jul 2010
Location: Arlington, TX
Posts: 161
Rep Power: 16
tcarrigan is on a distinguished road
To cboss:

Do you think you could post your setup, 0/nut, 0/k, 0/omega, fvSchemes, fvSolution, etc...?

I've been trying to simulate turbulent flow over a flat plate in OpenFOAM-1.6-ext for both a resolved grid with a y+=1 and an unresolved grid with a y+=60. I'm also using the kOmegaSST model with and without wall functions to handle both grids.

The problem I'm having is that when running the resolved grid using the kOmegaSST model, I'm slightly underpredicting the skin friction by just a few percent. However, when running the unresolved grid with wall functions for the kOmegaSST model, I'm severly underpredicting the skin friction.

Looking at your images, the behavior I'm seeing for the unresolved grid is similar to the behavior of the y+=30 grid you plotted in your third image when you were comparing the results of cases without using wall functions. This leads me to believe that either I'm not implementing the wall functions correctly, or the wall functions aren't being utilized during the simulation at all.

Thinking this was an issue with 1.6-ext, I installed OpenCFDs 1.6 version from mid February 2010, about the time of your original post. I reran the case using this version and observed the same behavior. So it seems it might be my problem.

Any help would be much appreciated.
tcarrigan is offline   Reply With Quote

Old   February 5, 2011, 07:46
Default
  #22
New Member
 
Join Date: Feb 2010
Posts: 24
Rep Power: 16
cboss is on a distinguished road
Hi,

nice, that this post is still recognized.

To your questions: The problem is, that I haven't been working with OpenFOAM for a long time, and that I don't have access to the done simulations. And it's quite complicated to get into it again, if you have neither a version of OF, nor any data. So I'm afraid, that I cannot give you a good advice.
Perhaps someone else can help.

Regards
cboss is offline   Reply With Quote

Old   February 5, 2011, 10:50
Default
  #23
Member
 
Maruthamuthu Venkatraman
Join Date: Mar 2009
Location: Norway
Posts: 80
Rep Power: 17
maruthamuthu_venkatraman is on a distinguished road
Hi,
Your answers are kept in Turbulence modelling for CFD by Wilcox . Just have a look at it how to set omega values at the nearwall cells. In general refer Ercoftac best pracise guidelines recommended BC's for external flows.

Good Luck. I dont think schemes will make big difference in this case.

Regards
maruthamuthu_venkatraman is offline   Reply With Quote

Old   November 13, 2011, 02:28
Default
  #24
Far
Senior Member
 
Sijal
Join Date: Mar 2009
Location: Islamabad
Posts: 4,558
Blog Entries: 6
Rep Power: 54
Far has a spectacular aura aboutFar has a spectacular aura about
Send a message via Skype™ to Far
Quote:
Originally Posted by cboss View Post
Nick,

(3) Yes, I set k as fixedValue=0.
In the original paper it is mentioned as flux = zero
Far is offline   Reply With Quote

Old   February 24, 2016, 04:52
Default
  #25
New Member
 
Yidao Dong
Join Date: Feb 2016
Posts: 4
Rep Power: 10
choux is on a distinguished road
Hello, cboss!
You said you were working on turbomachinery computations. I am wondering your progress because I plan to star my PhD research in this field. However, I am not familiar with this field. Could you recommend some review articles, especially thsoe with dynamic grids? Besides, could you give me some advice to seek some new research points in this field?
Best wishes!
choux is offline   Reply With Quote

Old   August 9, 2016, 10:53
Default
  #26
Senior Member
 
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 14
Eloise is on a distinguished road
Hello Foamer,

I'm digging out an old post with a validation case of a turbulent boundary layer over a flat plate. The details of the validation case are as in the first post of this thread.

I ran the case with two solvers (FineMarine4.2 and simpleFoam from OF2.2.1). I used the same mesh with both solvers, using the wall function (yPlus~60).

I compared the wall shear stress along the plate with Wieghardt's data in the attached figure. The results obtained with FineMarine match well the experimental data while the OpenFoam results are off.

However, if I check the drag force on the plate, I obtain the following values which are relatively close to each other:
OF -> Fx = 0.405871 N
FM -> Fx = 0.414316 N
Therefore, it looks like the OpenFOAM simulations are correct but that I actually don't post-process the wall shear stress properly.

I extract the wall shear stress using the wallShearStress and the sample utilities:
Code:
// Fields to sample.
fields
(
    wallShearStress
    wallGradU
    nut
);
sets
(
    plate
    {
        type        face;
        axis        xyz;
        start       ( 0.0  0.0 0.0);
        end         ( 6.0  0.0 0.0);
    }
);
Then, I compute Cf(x) = wallShearStress_X/(0.5*U_0^2)
omitting the density since simpleFoam uses values normalized with rho.

I also attempted to compute Cf(x) based on wallGradU:
Cf(x) = wallGradU_X*muEff/(0.5*rho*U_0^2) with muEff = rho*(nu+nut)
but it doesn't seem to be the proper way neither.

Both of those expressions for Cf seems to be wrong, is there anyone who can help me?

Regards,
Eloïse
Attached Images
File Type: jpg Cf(x).jpg (27.7 KB, 23 views)
Eloise 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
SST model swe704 Main CFD Forum 0 February 5, 2010 09:36
Flow Over Flat Plate Lance FLUENT 1 November 13, 2008 23:20
Half laminar and turbulent model trying to solve Andrew Clarke FLUENT 5 May 19, 2008 14:40
Turbulent flow over flat plate Narayanan Main CFD Forum 1 May 8, 2000 08:03


All times are GMT -4. The time now is 20:53.