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

Bad submarine drag force with SimpleFoam

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 30, 2015, 07:55
Unhappy Bad submarine drag force with SimpleFoam
  #1
New Member
 
Christian Whitefield
Join Date: Aug 2015
Location: Germany
Posts: 3
Rep Power: 11
Scarpafico is on a distinguished road
Hey,
I’m working on an external flow around a small submarine for quite some time now. I tried a lot of different settings and read many papers and posts here. I must say: a great forum!
Unfortunately I’m stuck now and need some help. My Problem:
I have experimental date which I cannot match! 64N was measured. Ansys CFX was easily able to get as close as 68N with SST. The closest I could get is 74N drag with Spalart-Almaras and 82N with komegaSST.
I optimized my geometry a few times and got good convergence in most of the cases. I tried initialization with potentialFoam or higher fvSchemes from the beginning with not much improvement. I used the motorBike-case as reference and included some higher fvSchemes after some time. Some of my settings/results for an example case:
  • OpenFOAM 2.3.1
  • Inlet water velocity 2m/s
  • komegaSST with k=0,0001588 and omega 0,0382
  • Y+ 12 … 22 (small areas with y+=1)
Please find the full information (fvSchemes, fvSolution, CheckMesh, p, U, omega, residual and force plot etc.) attached. Unfortunately I cannot post a geometry plot, but imagine a small torpedo-shaped submarine 3,5m long and with a diameter of maybe 0,5m.

I hope someone out there can give me a hint, how to get my drag force closer to the measured 64N!

PS: I calculated omega backwards with the cfd-Online-Tools by using TuL = 0,3m (10% of the body length was recommended somewhere here in the forum) and k=0,0001588. The simulations show a final omega of roughly 2000 … 5000 and k=2.8e-6 … 0.0381 in ParaFoam. Could that be the problem?

Cheers,
Christian
Attached Files
File Type: zip files_20150930.zip (82.1 KB, 28 views)
Scarpafico is offline   Reply With Quote

Old   September 30, 2015, 08:26
Default
  #2
New Member
 
Josh
Join Date: Jun 2013
Posts: 19
Rep Power: 13
joshm is on a distinguished road
Could it be due to your y+ falling in the buffer region? You'reusing the nutkWallFunction which is for y+ in the region 30~500 or so.
joshm is offline   Reply With Quote

Old   September 30, 2015, 12:01
Default
  #3
New Member
 
Christian Whitefield
Join Date: Aug 2015
Location: Germany
Posts: 3
Rep Power: 11
Scarpafico is on a distinguished road
Thanks for the hint. I started with Y+ ~ 1 in my first calculations. I'm at 30 to 50 now, but this calculation needs still some more time to converge! However, due to flow speed at the tip and the stern (aft), small faces and geometry curvature I still have areas with Y+ close to 5! Should I expect a larger impact from these small areas?

I will try to increase the boundary layer further without getting to much non-orthogonality
Scarpafico is offline   Reply With Quote

Old   October 3, 2015, 11:19
Default
  #4
New Member
 
Christian Whitefield
Join Date: Aug 2015
Location: Germany
Posts: 3
Rep Power: 11
Scarpafico is on a distinguished road

I managed to increase Y+ to the range of 40 to157. However the bow and some minor areas in the back are still around 14. I will try to fix this next week.
The drag force decreased to 62N, which would be fine when the pressure force wouldn’t be twice as high as the viscous force. Actually it should be the other way around!

Compared to the example case above I didn’t use cellMDLimited this time:
Code:
 
divSchemes
{
/* default Gauss linear;
div(phi,U) bounded Gauss upwind;
div(phi,omega) bounded Gauss upwind;
div(phi,k) bounded Gauss upwind;*/
//changed after 4500 iterations:
div(phi,nuTilda) Gauss linearUpwind default;
div(phi,U) Gauss linearUpwind grad(U);
div(phi,k) Gauss linearUpwind default;
div(phi,omega) Gauss linearUpwind default;
 
div((nuEff*dev(T(grad(U))))) Gauss linear;
and used limited 1.0 instead of 0.5
Code:
 
laplacianSchemes
{
//default Gauss linear corrected;
//changed after 4500 
default Gauss linear limited 1.0;
}
Can someone please help me to get out of this mess?!

Attached Images
File Type: png forces0-8500.png (36.4 KB, 19 views)
File Type: png residuals0-8500.png (84.9 KB, 18 views)
Scarpafico is offline   Reply With Quote

Reply

Tags
drag force, simplefoam, submarine

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
Force vectors for drag during sweeping motion aamer FLUENT 0 April 18, 2011 09:17
exporting drag force from fluent fluentguy FLUENT 2 October 27, 2009 15:19
drag coefficient & drag force abhishek.mnit FLUENT 0 April 30, 2009 00:48
Lift and drag force Arti Main CFD Forum 0 April 23, 2009 23:46
Airfoil Drag Force wowakai Main CFD Forum 3 October 13, 1998 20:27


All times are GMT -4. The time now is 15:25.