aspect ratio

- June 9, 2020 at 7:02 am
  
  obschti
  Subscriber
  
  Hello everybody!
  
  For my current project in Fluent is have to use the inflation tool. My first layer thickness is very small (~30µm) in comparison to the rest of the model due to y+. Therefore my aspect ratio is partially very bad (with a max of 3400).
  
  Might this become a problem with convergence? How can I solve that problem?
  
  Thanks in advance!
- June 9, 2020 at 1:17 pm
  
  Kalyan Goparaju
  Ansys Employee
  
  Hello,
  
  Such type of aspect ratios are expected in situations where finer mesh resolution is used to resolve the boundary layer. Ansys Fluent should be able to handle these situations. However, if you do notice any issues, especially in terms of stability of the solution, I strongly recommend increasing the mesh density in the wall-parallel direction to reduce the aspect ratio.
  
  Thank you,
  
  Kalyan
- June 10, 2020 at 6:58 am
  
  obschti
  Subscriber
  
  Hey Kalyan,
  
  thank you for your reply. Right now I just got confused about my desired y+ value while reading in some forums. I use SST model. What is a fitting desired y+ value to calculate the first layer thickness?
  
  Thank you!
- June 10, 2020 at 1:35 pm
  
  Kalyan Goparaju
  Ansys Employee
  
  Hello,
  
  The implementation of SST in Ansys Fluent is y+ insensitive. In other words, it will automatically use the appropriate techniques depending on the y+ of the mesh. So, the choice of y+ for your mesh is dependent on whether you are interested in integrating quantities all the way to the wall (y+~1) or whether you are OK with having wall functions approximate the near wall behavior (y+~>30).
  
  Thanks,
  Kalyan