- Nektar-users - imperial.ac.uk

Re: [Nektar-users] Reflection using APE Solver
by Sherwin, Spencer J 20 Oct '15

20 Oct '15

Dear Miguel, Kilian Lackhove (cc’ed above) has been working on this solver most closely so may be in a better position to response. However if you have set up a Riemann type solution at the boundary they should be a reasonable first attempt at non-reflecting boundaries. Can I ask what boundary conditions you are currently setting up? Cheers, Spencer. On 16 Oct 2015, at 13:30, Miguel Moratilla-Vega <M.A.Moratilla-vega(a)lboro.ac.uk<mailto:M.A.Moratilla-vega@lboro.ac.uk>> wrote: Dear Spencer, I am trying to solve the simple acoustic wave problem, imposing a Gausian pulse as an initial condition. I am using the APE solver to obtain the acoustic propagation, but at the boundaries of the domain I am having reflections. For that reason I was wondering if there is any method in Nektar implemented to avoid these reflection in the outer boundaries of the domain. I have tried using the Absorption forcing but it is not giving me any changes in the solution. I have noticed as well that for the Compressible Flow Solver there is a PressureOutletNonReflective boundary condition, so I don’t know if implementing this in the APE solver would solve the problem. In addition, I have found in a paper of Tam and Webb, that they developed a Radiation Boundary Condition that it has been applied by Groschel, Schroder et al. to minimize the reflection and applied to an APE problem. Thank you very much and kind regards, Miguel --------------------------- Miguel Moratilla-Vega PhD Student Aeronautical and Automotive Engineering Department Stewart Miller Building Loughborough University Leicestershire LE11 3TU 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 s.sherwin(a)imperial.ac.uk<mailto:s.sherwin@imperial.ac.uk> +44 (0) 20 759 45052

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Floquet stability analysis update
by Chris Cantwell 14 Oct '15

14 Oct '15

Dear all, We have now fixed one of the bugs which prevented the Floquet stability analysis part of Nektar++ from working correctly. The updates to the code are currently in the fix/floquet branch in the code repository. This will most likely be merged into the main codebase in the near future. We have tested the HalfMode variation of the code with a cylinder testcase and this accurately reproduces results from Barkley & Henderson (1996). I have attached example files for reproducing the critical case at Re=188.5/beta=1.585, which you should be able to run directly as follows. 1. Generate the time-periodic 2D base flow. IncNavierStokesSolver m32_base.xml This will also extract the field variables at a few history points which can be used to calculate the base flow frequency parameter "Freq", required for the following steps. Note that this simulation runs for 2000 time units, necessary to ensure the flow reaches a truly periodic state. 2. Generate the 2D base-flow slices for stability analysis IncNavierStokesSolver m32_slices.xml This will evolve the base flow for one period and create 32 slices (33 files, numbered 0 to 32) as checkpoint files which will be Fourier-interpolated to provide the base flow. 3. Run the 3D stability analysis. IncNavierStokesSolver m32.xml Note the specification of the base flow now uses the C-style printf format for specifying the baseflow slices. It should converge in around 20-30 iterations and the leading eigenvalue should be very close to 1.0. The "Re" (and therefore the "Freq") and "beta" parameters can be adjusted to compute the other Floquet multipliers from the paper. Note: there is still a bug with the SingleMode and MultipleModes mode types. We will update you when these are also fixed. Please let us know if you encounter any further bugs while using the HalfMode setting. Cheers, Chris -- Chris Cantwell Imperial College London South Kensington Campus London SW7 2AZ Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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Adding Body force for the Channel flow
by Jian Yu 06 Oct '15

06 Oct '15

Dear all, I am now trying to compute the channel flow using the Compressible Flow Solver. I have found the body force with derivatives non-trivial to add. Once the flow in a channel has reached a fully developed state, inertial forces in the channel, which are related to the mean favourable streamwise pressure gradient (pressure drop in a duct), are balanced with the wall friction forces. In this case, the body force f would be in the following form f=-tw/h, where tw is the wall friction containing velocity derivatives, h is the channel scale. Can anybody tell me how to perform this flow in Nektar? Thank you very much! Best Jian Yu

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OS X 10.11
by David Moxey 06 Oct '15

06 Oct '15

Dear all, For anyone that is interested in upgrading to OS X 10.11 (El Capitan), I can confirm that Nektar++ compiles, installs and passes regression tests. You will need to install the latest Xcode and install the new command line tools (go to the Terminal and run the command "xcode-select --install"). Additionally, for those that use MacPorts or Homebrew: 1) If you use MacPorts, you need to junk /opt/local and reinstall your ports. 2) If you use Homebrew, you probably need something along the lines of of brew update && brew doctor && brew upgrade. You will also need: 1) A small Nektar++ patch that can be found in the fix/osx-10.11-elcapitan branch. 2) A patch that you should apply to the boost static_assert.hpp header: https://svn.boost.org/trac/boost/ticket/11664 This will fix compiler warnings related to BOOST_STATIC_ASSERT. Cheers, Dave -- David Moxey (Research Associate) d.moxey(a)imperial.ac.uk | www.imperial.ac.uk/people/d.moxey Room 363, Department of Aeronautics, Imperial College London, London, SW7 2AZ, UK.

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Need help in stability analysis of flow over cylinder
by Uddin, Md (uddinma) 29 Sep '15

29 Sep '15

Uddin, Md (uddinma) has shared OneDrive for Business?files with you. To view them, click the links below. <https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> [https://r1.res.office365.com/owa/prem/images/dc-generic_20.png]<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> Cylinder(1).evl<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> <https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> [https://r1.res.office365.com/owa/prem/images/dc-generic_20.png]<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> Cylinder(1).xml<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> <https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> [https://r1.res.office365.com/owa/prem/images/dc-generic_20.png]<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> Cylinder-base(1).xml<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> <https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> [https://r1.res.office365.com/owa/prem/images/dc-generic_20.png]<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> Cylinder-Stability(1).xml<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/Documents/Ema…> 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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Uddin, Md (uddinma) wants to share the file Cylinder-base(1).xml with you
by Uddin, Md (uddinma) 25 Sep '15

25 Sep '15

To view Cylinder-base(1).xml, sign in<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/_layouts/15/a…> or create an account.

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Uddin, Md (uddinma) wants to share the file Cylinder-Stability(1).xml with you
by Uddin, Md (uddinma) 25 Sep '15

25 Sep '15

To view Cylinder-Stability(1).xml, sign in<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/_layouts/15/a…> or create an account.

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Uddin, Md (uddinma) wants to share the file Cylinder(1).xml with you
by Uddin, Md (uddinma) 25 Sep '15

25 Sep '15

To view Cylinder(1).xml, sign in<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/_layouts/15/a…> or create an account.

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Uddin, Md (uddinma) wants to share the file Cylinder(1).evl with you
by Uddin, Md (uddinma) 25 Sep '15

25 Sep '15

To view Cylinder(1).evl, sign in<https://mailuc-my.sharepoint.com/personal/uddinma_mail_uc_edu/_layouts/15/a…> or create an account.

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How to process "filename_eig_0" like file
by Hongfu Zhang 25 Sep '15

25 Sep '15

Hi All, I want to computethe eigenmode of a period field using BiGlobal Floquet analysis. I have gotten the "filename_eig_0" like file, how to do post-processing with this kind of file? Thanks very much for any help! Best Regards! Hongfu

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