[Nek5000-users] perturbation mode

[Antonios Monokrousos]

Hello!
I have a question about the pertubation mode of the code.

First I computed the base flow using the full non-linear solver and
letting it run until I get a steady solution. This worked fine.
Then I construct a perturbation which I add on the steady solution I got
before (base flow) with a very small amplitude, around 0.1%. The
solution, after I subtract the base flow looks good. (I'm comparing to a
different code).

Next I try to use perturbation mode since I want to use the exact
linearised Navier-Stokes and the problems appear.
I have the base flow and the perturbation in two different restart
files, which I specify in .rea file like this:
------------------------------------------------------
            2 PRESOLVE/RESTART OPTIONS  *****
meanflow.u
ic_pert_field.fld
------------------------------------------------------
I activate the perturbation mode (option 31 in .rea).

I damp both the solution of the base-flow and of the pertubation. I can
see that the code is solving for the base-flow (which it shouldn't) but
also has as initial condition the one that is supposed to be for the
The simulation blows-up after a few time steps.

I'm not sure I use the perturbation mode in the right manner.
Thanks in advance for any feedback or help.
Antonios


-- 
---------------------------------------------------------------------------------------------
Antonios Monokrousos
Department of Mechanics                 email:    antonios at mech.kth.se
Royal Institute of Technology (KTH)     phone:    +46 8 790 68 76
Osquars Backe 18                        telefax:  +46 8 796 98 50
SE-100 44 Stockholm, SWEDEN