Fluids

Fluids

I am doing an external flow simulation of a bus. When I tried to solve it I get a varying Cd?

    • JOELGEORGE
      Subscriber


      1. Model: Standard K-omega.
      2. Reynolds No: 18.63e^-06
      3. Boundary Conditions:

      Inlet - 22.22m/s Outlet - pressure outlet and gauge pressure set to 0 Pa. Bus body - wall, stationary non-slip condition. Rest of the zones are set as symmetry.

      4.Solution methods: Scheme - Coupled and rest as default. 


        Can anyone help me this. Thanks in advance.


    • aitor.amatriain
      Subscriber
      On the one hand, you get a varying Cd because the solution is not converged.
      Could you please show us a picture of the residuals? I guess that there will be various peaks and the mean values will be far from the converged values.
      On the other hand, you have a very poor mesh. Maximum orthogonal quality is 1 (the worst possible value) and the maximum aspect ratio is of the order of 10^(12). You should start working on this
    • JOELGEORGE
      Subscriber
      Ok thank you, I will work on my meshing. My geometry is imported and it needs surface repair. I am new to geometry clean up. Can you suggest any tutorials that might help me.

    • aitor.amatriain
      Subscriber
      What kind of problems do you have with your geometry? Could you post some pictures?
    • Rob
      Ansys Employee
      There are some tutorials if you click on "Help" and navigate to SpaceClaim or Fluent Meshing. The former lets you fix the CAD, the latter allows you to ignore some of the errors. Given a bus is more-or-less a box on wheels you may also have a transient eddy shedding issue to deal with.
    • JOELGEORGE
      Subscriber
      In SpaceClaim I did tried to remove the inexact edges, extra edges and I got a clean geometry with no errors, which was not the case initially.







      Thanks in advance.
    • aitor.amatriain
      Subscriber
      Why are you meshing the interior of the bus? This is not necessary for your case.
      In any case, I would recommend you to use Fluent Meshing. ANSYS Meshing is obsolete for CFD applications (with the exception of 2D meshing, as Fluent Meshing is not available in 2D).
    • DrAmine
      Ansys Employee
      ANSYS Meshing is still good for CFD Applications. You can use it or rely on Fluent Meshing Workflows to have a good mesh.
    • JOELGEORGE
      Subscriber
      For meshing I did create a mesh with tet. elements (Patch conforming algorithm), body sizing for the body of influence, face sizing for all the faces of the bus, and finally created a prism layer around the bus boundary.
      I would like to know how I could make orthogonal quality value in between 0.1 and 1.
      Thank you.




    • Rob
      Ansys Employee
      Have a look at the regions with poor skew. What is the cause of the poor skew? Post images and we (the community) may be able to give you some pointers.
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