[Nek5000-users] Divergent issue in Accelerating BL

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

Dear Nek users,

I ran into an odd issue I do not quite understand. I am working on an accelerating BL with relatively high RE (Re_{\delta*}_inlet = 8000) and this is how I did it:

I modified the available Blasius code in the NEK5000 such that it gives me the analytical profile for accelerating BL. Instead of using the pressure gradient to drive the flow, I used the analytical solutions as BCs at inlet and freestream. This approach works very well for low RE (Re_{\delta*}_inlet  ~ < 1500), however it gives me issue when I increase the RE (by decreasing viscosity P02); CFL increased significantly and started to fluctuate. If delta_t is large (~0.1) then eventually it quits for CFL being too large. If delta_t is small enough (~0.01) then it kept fluctuating. I plotted instantaneous u and v contours (I am doing 2D case)and I noticed many vertical streaks of unphysically high velocities across the domain, which is clearly a numerical issue.

I am not quite sure what is the reason contributing to this phenomenon. Could anyone help me on this?

Many thanks.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20181004/4d211987/attachment.html>