Hi,

I might be misunderstanding what it is you need, sorry for that, but have you tried to use the non stationary solver, gradually increasing Re from Re_0 up to Re_1, such that you maintain your solution, evan as it becomes unstable? For not so large differences in Re this might work.

Also, what do you need U_1 for? Do you want to superimpose U_1 onto U_0 to get an approximation of what the solution for Re_1 should be? I am not sure you can do this in a general case, and if you do, I think that choosing the right amplitude might be very tricky.

Cheers!
Stanisław Gepner

5 maj 2020 18:30 "A.P." <k210@list.ru> napisał(a):
Stanisław and Spencer,
 
it is impossible to use the selective frequency damping because my flows may have purely exponential leading eigenmodes.
 
I have checked the SteadyLinearisedNS examples and improve my xml file. 
 
The workflow now is:
(1) I calculate a stable velocity field U_0 by non-stationary solver at Re_0 and set this field as AdvectionVelocity.
(2) I set Re_1 > Re_0 and calculate a velocity field U_1 by SteadyLinearisedNS solver.
(3) Is it possible to find the physically reasonable amplitude for U_1?
 
Thanks.
 
 
Best regards,
Alex.
 

 
Вторник, 5 мая 2020, 4:48 +07:00 от "Sherwin, Spencer J" <s.sherwin@imperial.ac.uk>:
 
HI Both,
 
There should be examples of using the SteadyLinearisedNS in the directory solvers/IncNavierStokesSolver/Tests where it has been used for Re >>1 in stability analysis runs. Indeed I think there is a case at Re=7500. So possibly there is a SolverType setting that is wrong as Stan suggests.
 
Cheers,
Spencer.
 
 
On 4 May 2020, at 20:29, sgepner@meil.pw.edu.pl wrote:
 
Hi,
 
There is a steady state solver you might try. It was a while since I have attempted to use it, but I think you need to set the driver to SteadyState, and not change the Eqtype. Have a look at the manual sections 11.1.4 and 11.5.
 
My personal experience was, that it was easier for me to run the non stationary, standard solver towards a stationary solution, rather than to use the steady state one, even in the case of potentially unstable flows.
 
Hope this helps, cheers!
Stanisław Gepner
 
4 maj 2020 09:28 "A.P." <k210@list.ru> napisał(a):
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Hello,
 
I need to calculate a steady flow which may be unstable.
 
Is the option
 
<I PROPERTY="EQTYPE"  VALUE="SteadyLinearisedNS"/>
 
can be used only for Re<<1 or it is possble to make an appropriate AdvectionVelocity section for large Re?
 
Alex Proskurin.
 
 
 
 
 
 
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Spencer Sherwin FREng, FRAeS
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