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

Standing Wave: different solutions for different Courant and/or different Mesh

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 6, 2010, 10:40
Default Standing Wave: different solutions for different Courant and/or different Mesh
  #1
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 8
nuovodna is on a distinguished road
I'm trying to solve a standingWave but i have multiple different results with changing mesh params and Courant number.
Test cases:
BC : four walls
Dimension: 1x1x0.1 (2d)
1/nu = 1060
Mesh divisions along orthogonal flow direction : 100
200
400
Courant number: 0.5 / 0.1 / 0.05 / 0.01

Kinetic energy plots are different. On Courant numbers the 0.1 and 0.05 offer comparable solutions. Numerical schemes (ddtScheme, divScheme, gradScheme) are essentially non influential. Any idea/suggestion ??
nuovodna is offline   Reply With Quote

Old   May 7, 2010, 03:51
Default
  #2
Senior Member
 
Suresh kumar Kannan
Join Date: Mar 2009
Location: Luxembourg, Luxembourg, Luxembourg
Posts: 129
Rep Power: 8
kumar is on a distinguished road
what solver are you using. I had a similar expereince while using interFoam. The solution is very much mesh dependent and also very much dependent on CFL number.

bye
Suresh kumar
kumar is offline   Reply With Quote

Old   May 7, 2010, 05:18
Default
  #3
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 8
nuovodna is on a distinguished road
Yes, i m using interFoam 1.6.x . In my opinion, the difference of solutions seems to be related with viscous term. Have you any idea??
nuovodna is offline   Reply With Quote

Old   May 7, 2010, 05:27
Default
  #4
Senior Member
 
Suresh kumar Kannan
Join Date: Mar 2009
Location: Luxembourg, Luxembourg, Luxembourg
Posts: 129
Rep Power: 8
kumar is on a distinguished road
actually i am also studying a problem which involves waves but it is not a standing wave. I am studying liquid sheets. I was wondering if the problem is due to the surface tension term.

Also since my simulation is unsteady, i use second order schemes for time. In my experience the solution also varies a lot if you use different schemes. Just try doing that.
kumar is offline   Reply With Quote

Old   May 7, 2010, 06:58
Default
  #5
Senior Member
 
Emanuele
Join Date: Mar 2009
Posts: 110
Rep Power: 8
nuovodna is on a distinguished road
hi kumar thanks for your reply.

1-I tried three ddtScheme (Euler, backward and CrankNicholson) but they offer the same solution. I understand that backward and Crank Nicholson are the only 2nd order temporal schemes available.

2-Surface tension is not responsible in this case because i set it to 0.

3- I try as written in Couette Flow - The influence of viscosity
a very simple viscous flow and results were not good.
I'm thinking about the term

- fvm::laplacian(muEff, U)
- (fvc::grad(U) & fvc::grad(muEff))
// - fvc::div(muEff*(fvc::interpolate(dev(fvc::grad(U)) ) & mesh.Sf()))

in Ueqn.H.

I try the second formulation (commented in the file) and results changes a lot.
Maybe someone has find an alternate formulation (perhaps 2nd order) or find numerical schemes better to solve viscous problems without turbulence model.
nuovodna is offline   Reply With Quote

Old   May 7, 2010, 07:40
Default
  #6
Senior Member
 
Suresh kumar Kannan
Join Date: Mar 2009
Location: Luxembourg, Luxembourg, Luxembourg
Posts: 129
Rep Power: 8
kumar is on a distinguished road
Hello
Just one comment
how can the results of the Euler and Cranknicholson be the same if Euler is first order and Cranknicholson is second order.
In my case when i compare the results of the Euler case with the Cranknicholson case i see that the waves at the interface are damped in the first order scheme results and as a result of which the breakup of the sheet is much delayed.

regards
Suresh kumar
kumar 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
2d irregular grid Remy Main CFD Forum 1 December 22, 2008 05:49
basic of mesh refinement arya CFX 4 June 19, 2007 12:21
Icemcfd 11: Loss of mesh from surface mesh option? Joe CFX 2 March 26, 2007 18:10
pls help fluctuating residuals due to courant no sagar CFX 3 March 28, 2006 01:10
unstructured vs. structured grids Frank Muldoon Main CFD Forum 1 January 5, 1999 11:09


All times are GMT -4. The time now is 04:06.