[Nek5000-users] Finite-amplitude disturbance based on os7000

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

Dear Emily,


At that amplitude, you are seeing the nonlinear

effects - this is at it should be.


If you wish to compare against linear theory, then

the amplitude needs to be small enough such that the

u.grad u term is quite small.


I'm not certain of your ultimate objective -- if you're

trying to measure convergence, then a small amplitude

is important.  If you are interested in large amplitude

effects, then you won't be able to compare with linear

theory results.


hth,


Paul


________________________________
From: Nek5000-users <nek5000-users-bounces at lists.mcs.anl.gov> on behalf of nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
Sent: Friday, April 27, 2018 10:34:51 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Finite-amplitude disturbance based on os7000


Dear all,



First of all, thank you a lot for your help and feedback. The amplitude of ux’  in my case is 1.82E-1 which is superimposed on the base flow u = 1 – y**2 along with uy’ (this setting is identical to the literature paper). An order of BDF 3 is employed. Polynomial order is 8 with 4 elements in streamwise direction and 12 elements in the wall-normal direction. 1 wave length is simulated in the channel.



The default setting of os7000 was what I started. I have also tried to increase the spatial resolution, and reduce the time steps (dt = 0.05, 0.01, 0.005). However, it did not really change anything.  The distortion is less obvious if the magnitude of perturbation is decreased and totally disappears if it is as small as 1.82E-3.



Again, thank you a lot for the help and I will further explore the parameters and see what I can find.



Regards,



Emily
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