[Nek5000-users] Unrealistic values at element edges

[nek5000-users at lists.mcs.anl.gov]

Dear Neks,


I've been running turbulent channel and pipe flows using nek5000 for a while. However, recently when I created movies of lambda2 structures and pressure iso-surfaces in channel and pipe flows I observed some "strange" values at the edge between elements.


[cid:cec5092f-41be-4ae9-a468-a5fa9ab9f7ff]

This is lambda2 structures in turbulent pipe flow.


It is clearly visible from the picture that at some slices in streamwise direction, the values don't seem to be realistic and it feels like the flow is passing through some filters. Interestingly, when I plotted the mesh together with the variables, the vertical noise lines happened to be at the edge between adjacent elements, which is particularly clear in lambda2 plot. Same behaviour was also found in 2D pressure plots and in turbulent channel flow cases. Has anyone observed similar things before in visualisation?


I used both Paraview and VisIt for visualisation and the same thing was observed, so it shouldn't be a problem of software. In this case, I'm just wondering why the result is like this or is it because I set something wrong in my simulations?


Any comments will be appreciated and thank you very much in advance.


Best regards,

Tony
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