Dear Dr. Sherwin,


Thanks for the response. I look forward to hearing from you about the progress. Also it would be very helpful for my study if you can share the input files you are using to test the solver, once the problem is resolved.


Regards,

Arfan Uddin




From: Sherwin, Spencer J <s.sherwin@imperial.ac.uk>
Sent: Tuesday, September 29, 2015 12:29 PM
To: Uddin, Md (uddinma)
Cc: nektar-users; Ghia, Urmila (ghiau)
Subject: Re: [Nektar-users] Need help in stability analysis of flow over cylinder
 
Hi Arfan,

This is indeed the same problem and Chris and I are working very actively to sort this issue out and hope to have it sorted in the next week. There was a sign error in the FFT routines that was fixed a while back but since there was not a regression test for the Floquet stability it was not caught. 

Currently we are trying to reproduce the test that if you do a 2D floquet multiplier about a time periodic base flow the Floquet multiplier should be 1. Currently we are observing 1.04.  

Anyway hopefully some more news soon and a working version of the code.

Cheers,
Spencer.



On 28 Sep 2015, at 23:09, Uddin, Md (uddinma) <uddinma@mail.uc.edu> wrote:

Hello Dr. Sherwin,
Thanks for your reply. I saw a ticket, posted in 8/15/15, which detected some problem in floquet stability code. Is the problem you are mentioning the same? Can you give me an approximate timeline by when the problem will be solved?

I saw some results in the user guide for similar problem using this solver.  Was the results achieved by a different version. I am currently using version 4.1.0.

Regards,
Arfan Uddin



From: Sherwin, Spencer J <s.sherwin@imperial.ac.uk>
Sent: Saturday, September 26, 2015 7:44 AM
To: Uddin, Md (uddinma)
Cc: nektar-users
Subject: Re: [Nektar-users] Need help in stability analysis of flow over cylinder
 
Hi Afran,

We believe there is a problem with the Floquet solver which we are currently investigating.  We will certainly post the solution as soon as we find it. We can then check your case.

Cheers
Spencer 

Sent from my iPhone

On 26 Sep 2015, at 08:38, Uddin, Md (uddinma) <uddinma@mail.uc.edu> wrote:

Hi all, 

I am trying to do Biglobal floquet stability analysis of flow over a cylinder. My base flow has converged and I am getting the Strouhal numbers correctly for different Reynolds numbers. Then I tried to do the stability analysis, but I am not getting the desired results for floquet multipliers. I think there are some wrong settings in my input file that I am not able to figure out.

Can anyone look at my input files and help me figuring out the possible source of error?  Please check the attached files.

Here are the steps I am following:
1. Solve for the 2D base flow using UnsteadyNavierStokes equations. (Input file Cylinder.xml)
2. Get the base flow (.bse files) by taking 32 time slices over one period. (Input file Cylinder-base.xml)
3. Use the base flow to set up stability simulation for a specified LZ (Input fie Cylinder-Stability.xml)

The output .evl file is also attached.

General data: Re=220, LZ=2.4166, Expected floquet multiplier=0.45.

I am new to the solver. Any help will be greatly appreciated.

Regards,
Arfan Uddin
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Spencer  Sherwin
McLaren Racing/Royal Academy of Engineering Research Chair, 
Professor of Computational Fluid Mechanics,
Department of Aeronautics,
Imperial College London
South Kensington Campus
London SW7 2AZ

+44 (0) 20 759 45052