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

Free Surface Flows[Duncan's Exp & Wigley Hull]

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 15, 2011, 17:30
Question Free Surface Flows[Duncan's Exp & Wigley Hull]
  #1
New Member
 
Angela Wang
Join Date: Mar 2009
Location: Fairfax, VA, USA
Posts: 15
Rep Power: 8
Angela Wang is on a distinguished road
Send a message via MSN to Angela Wang
Hi foamers,

I wanna share my two cases with respect to free surface flows to see if anyone have same problems as mine. The 1st is the Duncan's Experiment, with a submergence of the hydrofoil as 1.034. The 2nd is the wigley hull case with Froude Number =0.316. Both of them are run with interFoam, laminar+Euler mesh, non-dimensionalized, OpenFoam 1.7.

The problems I have for the Duncan's Experiment:

there is a wake (an area where velocity jumps down) behind the trailing edge, see fig attached. I tried to run it as inviscid, and with different domains and meshes. It still didn't go away. Is it physically reasonable? Or is it caused by the numerical viscosity?

The wave elevation compares well with the experimental data with a little bit under-prediction.

The problems I have for the Wigley hull case:

While the wave elevation along hull compares well with the experimental data and the wave pattern seems good, the force calculated oscillates with time and the force coefficient shifts away off the experimental data. For C_w, 0.0015 is expected from the experimental measurement. However, my value oscillates around 0.0022. Does any one have similar experience? see fig attached.

** Cw=Np/(0.5*rho*U^2*S_w) where Np is the first term written in the forces.dat file (pressure_x), S_w wet area of half hull [the domain is set as symmetry].
Attached Images
File Type: jpg naca_wake_u.jpg (14.8 KB, 174 views)
File Type: png cd_converge_layout.png (11.1 KB, 123 views)
Angela Wang is offline   Reply With Quote

Old   February 29, 2012, 23:06
Default
  #2
Member
 
Dave
Join Date: Jul 2010
Posts: 97
Rep Power: 6
daveatstyacht is on a distinguished road
Angela,
I am a bit confused about your first issue with a speed drop in the foil wake. It is normal for the wake of an object to be slower than free stream in viscous flow though from what I can discern your issue is a region aft of the trailing edge slowing down sharply. Have you tried running the foil in a single fluid run (simpleFoam) to see if the behavior occurs without the influence of the free surface?

As for the Wigley hull, that is a good place to start for still water resistance validation. An issue that you need to be careful about for sub-critical Fn is wave reflections off of the outlet (and sides). The reflected waves can lead to oscillating forces. Also be aware that your choice of mesh and fvSchemes can have a very strong impact on the wave making (numerical dampening and diffusion). Good luck in your studies.

Regards,
Dave

Last edited by daveatstyacht; February 29, 2012 at 23:08. Reason: grammar
daveatstyacht is offline   Reply With Quote

Old   March 9, 2012, 05:43
Default
  #3
Senior Member
 
Join Date: Apr 2010
Posts: 151
Rep Power: 7
flowris is on a distinguished road
Angela,

If you send your files, I will take a look at them.

I have done a scaled Wigley simulation and also had oscillating forces. Their average compared well to experimental values from a towing tank. I believe this is what really happens in flows around hulls.

I also did simulations on a hydrofoil in water only, and now I am trying to move forward to foils near the free surface.
flowris is offline   Reply With Quote

Old   June 28, 2012, 12:58
Default drag on Wigley tutorial
  #4
New Member
 
Rafael Coelho
Join Date: Jun 2012
Location: Portsmouth
Posts: 22
Rep Power: 5
Rafael_Coelho is on a distinguished road
Hello I am quite new on OpenFoam and I am trying to calculate drag forces on the Wigley tutorial. Can anyone tell me what should I change?

Thanks you!
Rafael_Coelho is offline   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
Thermocapillary free surface flow zakifoam OpenFOAM Running, Solving & CFD 6 August 24, 2014 03:24
Free surface is below than expected..results are not good mechovator CFX 24 April 8, 2011 00:41
Submarine Free Surface samwh CFX 7 August 30, 2009 07:14
sphere in a free surface (thin film)flow Vasu Veerapaneni Main CFD Forum 0 September 15, 1998 17:32
Modeling Free Surface Flows Elliot Schwartz Main CFD Forum 5 August 25, 1998 21:03


All times are GMT -4. The time now is 00:12.