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

strange turbulent BCs work

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 11, 2010, 04:51
Default strange turbulent BCs work
  #1
Member
 
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 7
marine is on a distinguished road
hello dear foamers !

I'm simulating flow around a ship on OF1.6 with a mesh exported from StarCCM+.

I first tried a simpleFoam simulation with first order schemes and k-epsilon for modeling turbulence with BCS as follows :

k and epsilon = fixedValue at the inlet and zeroGradient at the outlet, wallfunctions on the hull.

My case didn't work as the continuity equation exploded after 30 iterations.

I think my mesh is correct because it worked on Fluent and STARCCM+ and the checkMesh only reported 4 skewFaces and few non orthogonal cells.

So I tried to modify the BCs for turbulence and I have now :

inlet : k=zeroGradient and epsilon=fixedValue
outlet : k=inletOutlet and epsilon=zeroGradient
(still wallfunctions on the hull)

I think it worked, I obtained coherent velocity and pressure fields (distribution and values) and forces of the same order as the ones I obtained on Fluent and StarCCM+.

My questions are : does someone know if this set-up is reliable or is not ? Does someone ever use this kind of set-up? because on the forum I only found cases where people fixed k and epsilon at the inlet and put zeroGradient for both at the outlet but it seems strange to me to impose values at the inlet where the flow is not "very" turbulent.

One more, what would be the best between wallfunction or fixedValue on the hull? (Re=111.6)

(I know the k-epsilon model isn't the best for this type of simulation but I want to compare with an old simulation using this model)

thank you in advance for your replies and advices !

Marine
marine is offline   Reply With Quote

Old   June 11, 2010, 05:18
Default
  #2
Member
 
Moritz Wied
Join Date: Mar 2010
Location: suttgart, germany
Posts: 35
Rep Power: 7
Mo-ITB is on a distinguished road
hey marine,

i am working on a similar problem at the moment, ahmed body aerodynamics. have you tried to make a polymesh in ccm+? this solved most of my problems, as it has much better quality.

bye,
moritz
Mo-ITB is offline   Reply With Quote

Old   June 11, 2010, 05:35
Default
  #3
Member
 
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 7
marine is on a distinguished road
yes my mesh is a polymesh, but I have a low density of cells in the volume (0.4).
My mesh doesn't seem to be the problem because with the turbulent BCs I choose for the second simulation it worked perfectly.
marine is offline   Reply With Quote

Old   June 14, 2010, 08:41
Default
  #4
Member
 
Marine
Join Date: Mar 2010
Posts: 38
Rep Power: 7
marine is on a distinguished road
To add precision : my case works with first order schemes, when I try with a second order scheme for convection (div(phi,U)=linear) it explodes...I'm know looking for a good 2nd order scheme If anyone have an advice?

thanks !

Marine
marine 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
Laminar doesn't converge; Turbulent models do? Amit FLUENT 11 April 23, 2015 22:55
LES and total turbulent kinetic energy Boerge FLUENT 1 September 8, 2012 11:41
Specfying Turbulent boundary-backward-facing step Ben Sellars FLUENT 1 December 13, 2006 08:39
Turbulent: Steady or Unsteady: confusion prem FLUENT 0 March 30, 2006 10:40
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 06:13


All times are GMT -4. The time now is 17:09.