[sandri_92]

Hi there! It's been a long time since my last post... I was then using fluent, and now I'm working as an intern and I have to fast learn Star-ccm+ to help my coworkers to do simulations ... They're pretty ambitius!

This time I want to do something that was easy in fluent & CFX. We want to make a 3D mesh, but use it for a 2D simulation. I mean, considering 3-axis, and the "depth" in the x-direction, the ZY plane should be refined, and have some nice inflation layers, but in the x-direction I want to have only one element (see screenshot mesh 3D & mesh ZY).

In fact, the problem I see here is that having only 2 or 4 elements in that direction doesn't allow me to have good results. If you see the residuals plot, you can check that x-momentum never is below 0.1, I've set as a stopping criteria 1e-4 for every equation (should be OK for our purpose, but next step is to calculate Y+ to check accuracy). And it's kind of non-sense to have more than 1 element, it multiplies the total amount of elements and gives no information, as the boundaries in the x-direction are set to symmetry walls. I've also tried with slip-walls, but I have the same problem, residuals don't go lower than 1e-3 (screenshot residuals).

The funny thing is only with 100 iterations (approx.) it gaves a good result (see screenshot velocity_106), and then at the 400th iteration weird things happens (screenshot velocity_1500)...

So people, what am I doing wrong? Is it possible to have only one element in that direction? I've tried a volumetric control (with all the geometry inside it), and applied a trimmer, anisotropic meshing (taking care in the x-direction), but the minimum number of elements I get is 2.


Some extra info:
-This is a simple simulation involving a flat plate located vertically. The size is (x,y,z)=1, 0.1, 1 (meters). The "wind tunnel" is about (1, 20.1, 11).
-The CD coefficient I want to get is about 1.9 (Frank White as reference).
-Simulations are carried in star-ccm+ 9.02. Local parallel (4 processors).

Thanks in advance!

Sandra.