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Need help with post processing transient simulations |
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#21 | |
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Lucky
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Quote:
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#22 | |
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Filippo Maria Denaro
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#23 |
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When I started this thread, I was only interested in knowing if I could post process anything useful with a partial simulation but seeing the general direction this thread is going in, I think I should give some physical clarifications.
The Re based on the inlet diameter is only 2000. The expansion ratio is 2 so the Re after expansion decreases to 1/4th of 2000. Transitional flow is triggered partly by the geometry (diverging c/s) and partly due to the perturbation I am imposing on the inlet BC. Since I am reproducing an article, I am giving all BCs as the author gave; hence the inlet paraboloid UDF with perturbation and so on. What LuckyTran also says about the usage of the word DNS is right; this is a spatial localized problem and that is why I have a very fine mesh only in the expansion area. Of course, it can be questioned as to how did I decide till where to make the mesh fine but then again since I am reproducing an article, I already know till where approximately the mesh needs to be fine. |
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#24 |
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Filippo Maria Denaro
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Could you post a link to such paper?
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#25 |
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Filippo Maria Denaro
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#26 | |
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Lucky
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So the inlet is not turbulent and parabolic velocity profile is appropriate. Inside the domain then, you solve for everything so there are no worries. |
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#27 | |
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Filippo Maria Denaro
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Yes but the theory assumes the Re_D for a pipe developing infinitly downward... Conversely, You should consider here a pipe ending at a certain x due to the expansion that changes the pressure condition... |
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#28 |
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Lucky
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The inlet comes from a long pipe from which you can assume it has developed infinitely and that any possibility of turbulence has been damped out by the walls. Inside the domain is DNS so there are no worries. You can assume that the inlet is parabolic.
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#29 | |
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Filippo Maria Denaro
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My idea is that for Re_D not more than 2000 it could be still reasonable to set a parabolic profile at the numerical inlet but considering thereafter at least 10-15 diameters of pipe lenght in the computational domain to let the flow developping according to the pressure change in the expansion. With the correct grid resolution the simulation could be an acceptable reproduction of the onset of turbulence. A similar problem was simulated in this old paper: https://engineering.jhu.edu/fsag/wp-...6/JFM_1999.pdf in their case the authors assumed a turbulent inflow |
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Tags |
dns, post procesing, transient |
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