Different first layer cell height for different pipe diameter?

    • habibulaqil97

      Hello all,

      Should I change different first layer thickness value for inflation inside my pipes with different diameters? I currently making a simple fluid flow simulation from a pipe with 206mm ID which flow through a reducer and another pipe with 102 mm ID. From my understanding and according to this guide here (correct me if I am wrong), change in diameter will result in change of Reynolds number which also affects other values needed to calculate first layer cell height value such as skin friction constant Cf, shear wall stress tw and frictional velocity Ut.

      Let me know what you guys think.

    • Rob
      Ansys Employee

      You're aiming to resolve the near wall flow, so need to decide what mesh resolution is needed. The meshing tool doesn't know what the Re will be, so provides default heights based on the shape and other global size settings. 

    • habibulaqil97

      Hello rwoolhou,

      Honestly, I do not get it. I have calculated the Reynolds number in each part of the pipe and I know according to Reynolds number equation, Re should decrease as there's a sudden decrement of diameter. Should I manually and separately set the first layer cell height according to the diameter of pipes which are 206 and 102 mm respectively or not, therefore the first layer cell height for all parts of my pipe system are the same?

    • Keyur Kanade
      Ansys Employee

      The diameter is almost half. 

      Re also depends on other factors. 

      I suggest you to use different first layer height if you can. If not you can go ahead with smaller first height. 




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