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#1 |
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Hi all, I want to ask what are the consequences of using to thin boundary layer in meshig of the domain. I perform simulaiton of axial fan (I simulate 1 blade) with Re=10^6 and diameter of 1.5 m. While doing mesh independent studies I noticed following observation. I meshsed domains 2 times, one time with inflation layer first node placed for 1 m dimension (which is suitable for geometry) and one time for 0.3 m (what gives relatively thinner first layer of the mesh). I perform the simulation in ansys 11 and ansys 10 cfx version having following results: a) cfx ver. 11 and "thick" first element of boundary layer - mass flow of 2.85m3/s and nice convergence b) cfx ver. 11 and "thin" first element of boundary layer - almost the same mass flow and convergence c) cfx ver. 10 and "thick" first element of boundary layer - mass flow of 1.3m3/s and big problems with convergence d) cfx ver. 10 and "thin" first element of boundary layer - the same situation as for version 11,the same flow, everything ok. e) cfx ver. 10 and "thick" first element of boundary layer and 4 times denser mesh - mass flow was again in range of 1.3m3/s and big problems with convergence
Every other parameters are exactly the same. The simulaitons vere performed few times to ensure. Can anyone explain it? Luk |
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#2 |
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I hope you mean mm's for your first node height
![]() In general your solution should become better if you refine your boundary layer area (when your solving up to the wall), but if you're using wall modeling this isn't necessarily true. |
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#3 |
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Hi, Yes,it is in mm. My problem is that every other parameter of the mesh and simulation is the same (Y+ is set to 11 in both cases, I use k-e model with scalable wall functions). The strange thing is that there are differences between cfx versions and overall differenfce in flow image. I am not yet sure about other mesh densities.
Luk |
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#4 |
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Hi Luk,
I can't imagine that the thickness of boundary layer is the reason of your convergence problem?! Which conditions do you apply on Boundaries (Inlet/Opening/Outlet)? I had made the experience the mass flow has to be set an Inlet, and Outlet Total pressure, or sometimes like better to implement as Opening (Re-Flows!!) If I switched the boundary conditions i had also various problems with the convergence... |
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