{"id":314494,"date":"2023-11-02T07:59:25","date_gmt":"2023-11-02T07:59:25","guid":{"rendered":"\/forum\/forums\/topic\/mesh-independence-study-4\/"},"modified":"2023-11-06T16:41:25","modified_gmt":"2023-11-06T16:41:25","slug":"mesh-independence-study-4","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mesh-independence-study-4\/","title":{"rendered":"Mesh Independence study"},"content":{"rendered":"

Hi to all,<\/p>\n

I am working on a 3D airfoil. Currently, I am doing a mesh independence study to assess the dependence of the simulation results.
For this purpose, I plot the two parameters CL and CD when calculating. My solver is Fluent and I use K-W SST<\/em> turbulence model. My mesh is the structure that I produced in icem-cfd. 
I first started with a 552K<\/em> cell mesh with  Y+ <1<\/em> , and the residuals converged very well. which is according to the following figure:<\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

 <\/p>\n

Now, I increased the number of grid cells to 1,263,000 cells, but unfortunately, this time, the residuals fluctuate strongly and do not intend to converge, and I also receive the message (Stabilizing pressure coupled to enhance linear solver robustness.) repeatedly when solving, which is as follows:<\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

I really wonder why this is happening. To create a new mesh, I did not change the growth rate of the block lines at all, and only increased the number of nodes of the block lines, and at the end, I checked the mesh quality parameters, which were very good.<\/p>\n

Mesh 1:  (has very good convergence)<\/p>\n

Aspect Ratio: 1-5700<\/p>\n

Determinant : 0.87-1<\/p>\n

Orthogonal Quality: 0.82-1<\/p>\n

Quality: 0.87-1<\/p>\n

Skew: 0.69-1<\/p>\n

 <\/p>\n

                                            Mesh 2:  (has very bad convergence)<\/p>\n

Aspect Ratio: 1-5660<\/p>\n

Determinant : 0.895-1<\/p>\n

Orthogonal Quality: 0.837-1<\/p>\n

Quality: 0.87-1<\/p>\n

Skew: 0.674-1<\/p>\n

 <\/p>\n

If you pay attention, you can see that even the quality of the second mesh is a little better than the first mesh, but its convergence is much worse and full of (Stabilizing pressure coupled to enhance linear solver robustness.) messages.<\/p>\n

The aspect ratio of the network is as follows, which shows the elements behind the airfoil:<\/span><\/span><\/span><\/p>\n

 <\/p>\n

 <\/p>\n

Now, I increased the network behind the airfoil and found that my non-convergence problem was solved:<\/span><\/span><\/span><\/p>\n

 <\/p>\n

 <\/p>\n

See, with the increase in the number of cells behind the airfoil, my network has increased from 1,263,000 cells to 2,000,000 cells, which takes time to solve.<\/span> If this amount of cell increase is applied on the surface of the airfoil, it gives much more accurate results than applying  at the back of the airfoil.<\/span><\/span><\/p>\n

In many papers, I have seen that the mesh behind the airfoil is gradually enlarged up to the outlet pressure boundary condition, which is as follows:  but it gives me a message of non-convergence.<\/span><\/span><\/span><\/p>\n

 <\/p>\n

Why do I have to make the grid behind the airfoil so small to solve the problem of its non-convergence? Do you have a method or an idea to solve the problem of its high aspect ratio without increasing the cells behind the airfoil?<\/span><\/span><\/span><\/p>\n

 <\/p>\n

Thanks in advance<\/span><\/span><\/span><\/p>\n

Regards<\/span><\/span><\/span><\/p>\n","protected":false},"template":"","class_list":["post-314494","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t