{"id":314685,"date":"2023-11-03T06:00:10","date_gmt":"2023-11-03T06:00:10","guid":{"rendered":"\/forum\/forums\/topic\/mesh-independence-study-for-airfoil\/"},"modified":"2023-11-03T06:00:10","modified_gmt":"2023-11-03T06:00:10","slug":"mesh-independence-study-for-airfoil","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/mesh-independence-study-for-airfoil\/","title":{"rendered":"Mesh Independence study for airfoil"},"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

\"\"<\/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

\"\"<\/p>\n

 <\/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

\"\"<\/span><\/p>\n

 <\/p>\n

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

\"\"<\/span><\/p>\n

 <\/p>\n

See, with the increase in the number of cells behind the airfoil, my mesh 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 other words, I think that the mesh behind the airfoil does not need a significant increase to solve the convergence problem, and if this mesh increase is applied to the surface of the airfoil, I will get accurate results closer to the Experimental results.<\/span><\/span>  Increasing the grid behind the airfoil solved my convergence problem though.<\/span><\/span><\/span><\/div>\n
 <\/div>\n
<\/div>\n
 <\/div>\n
I have seen in many Paper that the mesh behind the airfoil is gradually enlarged to the end, which is as follows: But when I gradually enlarge the mesh behind the airfoil to the end, the flow does not converge:<\/span><\/span><\/span><\/div>\n
 <\/div>\n
\"\"<\/span><\/span><\/span><\/div>\n

 <\/span><\/span><\/span><\/p>\n

I also used the following ratios on the lines of the blocks:<\/span><\/span><\/span><\/p>\n

\"\"<\/span><\/p>\n

Are these Ratios suitable?<\/span><\/span><\/span><\/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

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

Regards<\/span><\/span><\/span><\/p>\n","protected":false},"template":"","class_list":["post-314685","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["17026","13659","199"],"_bbp_author_ip":["23.52.43.88"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["908"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["314685"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","13659","17026"],"_bbp_voice_count":["3"],"_bbp_reply_count":["7"],"_bbp_last_reply_id":["318186"],"_bbp_last_active_id":["318186"],"_bbp_last_active_time":["2023-11-17 13:55:46"]},"test":"a-karimi8457gmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/314685","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/314685\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=314685"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}