[Nek5000-users] Nek5000 documentation details: Pn-Pn pressure solver

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

Dear Neks,

reading the documentation I got the impression that Pn-Pn solver (low Mach) first solves the pressure where the convective and viscous (!) terms are taken into account. After that using this p^{n+1} we solve for velocity field. It seems that the algorithm consists of only 2 steps (pressure + velocity).

However, reading the paper by Tomboulides, Lee, Orszag (1996) which is referenced inside the code, I see the projection algorithm where first the velocity is updated using the extrapolated convective term, then the Laplacian of pressure is calculated due to convection, after that the velocity is updated using convection and pressure gradient. The last step accounts for viscous term.

I am a bit confused, could you please help me out here? Which method is used?

PS. Another thing is the coupled Helmholtz solver in Pn-Pn. I see that in case of Pn-Pn-2 each velocity component is treated separately (segregated solver). However, this coupled thing slightly confuses me, why not treating it separately as in Pn-Pn-2? Could you please comment there as well? Thank you.

Best regards,
Vlad