Y plus for transition sst

- March 24, 2020 at 2:51 pm
  
  ashwin11
  Subscriber
  
  I am using transition SST in Fluent to model flow mixing inside curved tubes with multiple inlets and outlets (aorta model). How do I ensure that my y+ values are within 1 as suggested in the documentation? I did a steady state first and checked that y-plus values are within 5.2 (Is this acceptable?). But my actual simulation is transient. How do I get y+ values for transient cases?
- March 24, 2020 at 5:28 pm
  
  Kalyan Goparaju
  Ansys Employee
  
  Hello,
  
  The Transition SST k-omega is a y+ insensitive method. Though y+~1 is recommended so that the boundary layer is accurately resolved, this technique can handle meshes that have higher y+. Your y+ of 5.2 is a reasonable enough to get started.
  
  Thanks,
  
  Kalyan
- March 25, 2020 at 8:07 am
  
  ashwin11
  Subscriber
  
  Thanks a lot for the quick reply. But in transient cases, should I take a time average of y+ plus to ensure that the boundary layer is resolved properly at all timesteps?
- March 25, 2020 at 1:19 pm
  
  Kalyan Goparaju
  Ansys Employee
  
  Hello,
  
  I would instead recommend using a y+ calculator (https://www.cfd-online.com/Tools/yplus.php) and enter the expected mean values of your transient simulation to get a reasonable estimate of the y+ value. Based on this value, you can change your grid appropriately to resolve the BL.
  
  Thanks,
  
  Kalyan
- March 27, 2020 at 11:01 am
  
  ashwin11
  Subscriber
  
  This is a great tool. Thanks for the suggestions. The L_Boundary Layer is the diameter of the tube where the inlet is, if I am right?
  
  Regards
  
  Ashwin