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

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 ??

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

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??

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.

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 http://www.cfd-online.com/Forums/ope...viscosity.html
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.

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