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<p class="MsoNormal">Dear Nek users,</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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:
</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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. </p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am not quite sure what is the reason contributing to this phenomenon. Could anyone help me on this?</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Many thanks.</p>
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