[Nek5000-users] Elsasser subroutines in the MHD solver

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

Hi,
I am simulating a flow in a rotating spheroidal shell (made from a cubed 
sphere grid) with a periodical forcing and no-slip boundaries for the 
velocity.  Without a magnetic field, this is working great. I recently 
tried my hand on dynamo simulations and tried to adapt quasi vaccum (n x 
B = 0) boundary conditions for the magnetic field. I have a local 
orthogonal coordinate system on the surface, where I set the two 
tangential components of B to 0 and use div B = 0 to find a value for 
the normal component . This vector is then transformed back to cartesian 
coordinates and used in userbc. This is of course a bit ad hoc and needs 
further testing.
However, I am not quite sure in how the MHD implementation in Nek5000 
actually works and wether it can be used for my problem. As far as I 
understand, the Elsässer formulation is mainly used for MHD turbulence. 
My main questions for further testing are
1) Is a kinematic dynamo possible with Nek5000? (we already have data 
from a finite volume code of kinematic dynamos for comparison)
2) Since the Elsasser variables combine u and B, are the forcings in 
userf actually seperate? I used "if (ifield .eq. 1)"  in userf, so that 
the forcing only adds to the velocity field, but the B field starts to 
grow before u.
As mentioned in the earlier mail, I already looked in the source code, 
but couldn't get any clear answers.

Cheers, Jan