i don’t know why it become supersonic.

- May 18, 2023 at 10:27 am
  
  seung mook park
  Subscriber
  
  i only change density constant to ideal gas.
  i don't know why it become supersonic.
  it is PBS and my inlet condition is
- May 18, 2023 at 11:24 am
  
  NickFL
  Subscriber
  
  First thing, check your dimensions. Sometimes when importing the mesh we accidentally import it in mm when we want m or something. This is typically a consequence of such a mistake. In the first image you are also at 700 m/s. I do not know what material and pressure you are at, but I would image this should be a compressible flow. What did your hand calculations give you for a max velocity?
  - May 19, 2023 at 2:13 am
    
    seung mook park
    Subscriber
    
    working fluid is air, inlet condition is 192 kPa, 2067K, 0.007551m^2 and my hand calculation result is 673m/s.
    it is not supersonic at inlet.
    - May 19, 2023 at 7:35 am
      
      NickFL
      Subscriber
      
      it is not supersonic at inlet.
      If it is not supersonic at the inlet, then go back and review the boundary conditions. The outlet boundary is supersonic in your calculation. This means, if you were expecting subsonic flow, that there is a problem here. When the flow is supersonic it uses the upstream inlet conditions and the downstream is swept away (the characterstics of the equations do this).
    - May 19, 2023 at 8:26 am
      
      seung mook park
      Subscriber
      
      you mean i have to change my outlet boundary conditions?
    - May 19, 2023 at 8:28 am
      
      NickFL
      Subscriber
      
      Review: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/flu_ug/flu_ug_sec_compress_inputs.html?q=modeling%20inputs%20for%20compressible%20flow
    - May 22, 2023 at 1:54 am
      
      seung mook park
      Subscriber
      
      Thank you for answering!