Preprocessing

Preprocessing

How to determine the y+ values for k-omega SST model?

    • Abdallah1996
      Subscriber

      Hello Everyone,


      Im performing a CFD study using ANSYS 18.1 on a 3D inverted Ahmed model to investigate the effect of an active underbody rear diffuser (Re > 1.4 e+6), my study was supposed to be performed using a wind tunnel, but due to the corona pandemic, i had to change the method to CFD, which is new to me, so i have some questions if anyone can help.


      1- is there a specific rule for the enclosure (domain) dimensions? i made it 10-12 times the model L,H,W.


      2- how can i perform a local refinement for the area around the model in ANSYS 18.1?


      3- im using the k-omega SST turbulent model as it predicts well near walls and combines the benefits of k-epsilon and k-omega, what value for y+ should i aim for? and is there a redcommended limit for the number of inflation layers? as if i aim for y+ around 1, the inlation layers are barely visible when zoomed in.


      4- should the inflation layers size and growth rate be the same on the walls and on the model surface?


      Appreciate your help guys

    • Keyur Kanade
      Ansys Employee

      first please upgrade to latest release 2020R1. 


      use 5 times infront, 10 times in rear, 5 to 7 times on sides. you can use symmetry to keep cell count low. 


      you can use body of influence for refinement. please check following. 


      https://studentcommunity.ansys.com/thread/body-of-influence-for-sizing/


      if you are using k-w sst, you need fine meshing near wall. you should aim for y+ ~ 1 to 5. 


      Regards,


      Keyur


       


      If this helps, please mark this post as 'Is Solution' to help others.


      Guidelines on the Student Community


      How to access ANSYS help links


       


       

    • Abdallah1996
      Subscriber

       Thank you for the reply,


      unfortunately, im not able to update to newer versions as this is the newest version available from my university.


      i have applied symmetry to my model, but, how is this going to affect my CFD simulation? and do i have to use half of the model area in the reference valuies?


      also, aiming for a y+ value of (1-5) will lead to very small elements in the inflation layers which will have big size difference from the next tetrahedral elements in the coarse mesh far away from the model as shown in the picture, any idea how to solve that?


    • Keyur Kanade
      Ansys Employee

      in fluent you can define symmetry boundary condition. please go through help document for the same. 


      to reduce jump from prism to tet, please use different inflation method. 


      please have a look at 



      please ask university to get latest 2020R1. 


      Regards,


      Keyur


       


      If this helps, please mark this post as 'Is Solution' to help others.


      Guidelines on the Student Community


      How to access ANSYS help links


       

Viewing 3 reply threads
  • You must be logged in to reply to this topic.