Fluids

Fluids

First cell height/2 or (Yp) < Roughness Height(Ks) in 3D ABL flow steady simulation?

    • DIWAS
      Subscriber

      Hello everyone, I have seen many threads but could not find a good solution method. I have also read the documentation that Fluent doesn't allow Yp to be less than Ks. I have seen some papers like this "Numerical simulations of development of snowdrifts on long-span spherical roofs" where Ks=0.06 is greater than the first cell height(0.01m) and Cs is 0.9. How to apply these conditions to get a good results. When I keep the Ks and Cs as 0.00058 and Cs as 0.5 it seems ok but when I increase these two values the results are totally messed up.

    • Rob
      Ansys Employee
      Y+ and any other wall based roughness models will be a little messy when you add a few mm/cm/m of snow to the surface: this is why we mesh to resolve the flow and physics rather than blindly following guidelines that were developed for smooth wings.
    • DIWAS
      Subscriber
      Thankyou for your helpful response, but I am not dealing with wings. Simply, I am dealing with a cube inside a domain(consider a flat roof). Then, is it impossible to do it?
    • Rob
      Ansys Employee
      It's not impossible, you just need to be very careful with settings. If you're setting a roughness that's comparable to the near wall cell height then consider if you should be resolving the rough surface: the models are there to make things easier. If you are adding a load of snow to the roof you may want to ensure the inflation and (relatively) low aspect ratio mesh are thicker than the expected pile of snow.
    • DIWAS
      Subscriber
      thank you so much, I will try to apply it on the mesh and check the inflation as well.
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