Fluids

Fluids

Y plus for transition sst

    • 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? 

    • 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

    • 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? 


       

    • 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

    • 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

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