[Nek5000-users] param 31

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

Hi Neks,

I would like to use Nek5000 to perform the stability analysis based on a 
time periodic base flow.

To do this, I need to introduce my base flow that changes with time, 
thus I need to update the base flow each flow iteration.

I have seen that if param(31)=-1, nek5000 considers constant base flow, 
however if param(31)=1 it considers time variable base flow. Could you 
explain me the difference?

I suppose that if param(31)=-1 I introduce the base flow in the first 
time step,
however, what should I do if param(31)=1?

I did the following tests. Assuming that u,v,w are the vectors 
containing the base flow, I have tried two different things:

1) considering param(31) = -1
    call opcopy(vx,vy,vz,u,v,w) ! update the base flow each time 
iteration

2) considering param(31) = 1
    call opcopy(vx,vy,vz,u,v,w) ! update the base flow each time 
iteration

I obtain different results, and I would like to know the difference and 
what would be the correct option to solve my problem.

Even if I don't update the base flow, the results that I obtain are 
different using
param(31)= +1, -1.

Finally, I have found that vxp, vyp, vzp are the perturbed variables u', 
v', w' (please, correct me if I am wrong). Is there any way to plot only 
these variables?

Thank you in advance.
Cheers
SL