- Nektar-users - imperial.ac.uk

JFM Paper on Instability Suppression Published
by Abhishek Kumar 23 Jun '25

23 Jun '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear all, I hope you're all doing well. I’m pleased to share that our paper, *“Suppressing instabilities in mixed baroclinic flow using an actuation based on receptivity,”* has now been published in the *Journal of Fluid Mechanics*: https://doi.org/10.1017/jfm.2025.10241 The study presents a receptivity-based strategy to suppress instabilities in a mixed convective flow, with actuation designed from adjoint eigenmodes. The work builds on our previous stability analysis and was carried out entirely within the Nektar++ framework. Some of the earlier results were presented at a previous Nektar++ meeting. I’ve attached the published version in case it’s of interest. Unfortunately, I won’t be able to attend this year’s Nektar++ meeting due to personal circumstances. I wish you all a successful and enjoyable meeting! Best regards, Abhishek

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Nektar++ 5.8.0 Released.
by Chris Cantwell 16 Jun '25

16 Jun '25

Dear all, We are pleased to announce the release of Nektar++ v5.8.0. As always, if you encounter any problems please feel free to contact us on the mailing list nektar-users(a)imperial.ac.uk. You can also report bugs and issues on our issue tracker (https://gitlab.nektar.info/nektar/nektar/-/issues) This release includes a range of new features and improvements over the 5.7.0 release: **Library** - Use GLL quadrature points on Tri Dirichlet BCs with CG (!1895) - Add FieldConvert module to perform local stability analysis for compressible flows (!1319) - Remove get() accessor from Array data structure (!1937) - Fix issue with `StdTetExp::v_LocCollapsedToLocCoord` (!1946) - Fix issue with `NodalTriExp::v_GetTracePhysVals` (!1951) - Remove deprecated version of v_SetCoeffsToOrientation functions (!1954) - Fix issue with Dirichlet BCs when using variable P (!1972) - Patch for implicit-function error in scotch-6.0.4 (!1938) - Tidy virtual inheritance in NodalTriExp (!1979) - Fix partial overload virtual function in AssemblyMap, StdRegions, and LocalRegions (!1978) - Fix partial overload virtual function v_PhysEvaluate (!1980) - Matrix free ops shape cleanup (!1735) - Fix NodalTri processing and static condensation matrix release (!1989) - Fix third-party Scotch patch (!1998) - Fixed Modified Arnoldi driver to remove discontinuities from random vectors (!2002) - Addedd support for backing up filters output when the file name have already existis (!2006) - Partially revert Geometry::v_ContainsPoint (!2007) - Make the CWIPI third-party patch work with IntelLLVM (!2053) - Use C++17 value template for traits (!2081) - Add H1-norm to Error filter (!1834) - Delete redundant lines in the Navier-Stokes diffusion functions (!2058) - Various tidy-up for solvers (!2056) - Add Compilation option for boost filesystem (!2092) - Update minimum Cmake version to 3.10 (!2096) - Deprecated FR method (!2102) - Remove some boost include in favor of C++17 build-in features (!2097) - Various tidy-up in SolverUtils (!2100) - Use forward declaration in header files for GlobalMapping (!2099) - Remove dummy `APESolver` executable. (!2119) - Tidy use of boost_lexical_cast (!2109) - Tidy-up SpatialDomains (!2120) - Remove NekInt, NekInt32, NekInt64, NekUInt, NekUInt32, NekUInt64 typedef (! 2123) - Fix CMake warnings related to modern policy changes (!2129) - Add support for unsigned int in SessionReader parameters (!2127) - Put in check for variable p diagonal preconditioner (2132) **CI** - Fix CubeAllElements performance test tolerance (!1943) - Remove `allow_failure` from compiler warnings and formatting (!1958, !1966) - remove CI image tag when dockerhub deploy completes (!1960) - Use recursive strategy for submodule (!1997) - cleanup CI environment images after packaging (!1991) - Update Fedora test environments to Fedora 40 (!1993) - Fix broken Fedora packaging library dependency (!2160) **NekMesh** - Add high-order pyramid and prism support from gmsh (!1956) - Industrial Pipeline Mesh Curving and CAD-Mesh link Reconstruction for all type of elements (!2057) **Python** - Transition bindings to use pybind11 (!1950) **Documentation** - Updated the User-guide with additional inofrmation for outflow BC, addressing the issue #103 (!1990) **PulseWaveSolver** - Added ability to output history points (and other filters) (!2000) **Miscellaneous** - Deprecate use of TimeIntegrationMethod in SolverInfo (!2059) Kind regards, Chris -- Chris Cantwell Reader in Computational Engineering Director of Postgraduate Studies (PhD) Department of Aeronautics Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0)20 759 45050 Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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Planar Jet Flow with Predefined Velocity Distribution
by Diksan Muhammad 04 Jun '25

04 Jun '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Hi, I am new to Nektar++. I want to simulate planar jet flow with predefined velocity distribution, based on a csv file. Any recommendation from which tutorial should I start and which tutorial does provide an example of employing arbitrary distribution for a boundary condition? Best Regards, Diksan M

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build issues with versions 5.6.0 and 5.7.0
by Aidan Forknall 04 Jun '25

04 Jun '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Hi I am having issues compiling fresh installs of nektar v5.6.0 and v5.7.0 onto a linux workstation. The tar.gz files are downloaded from nektar src. Once extracted I follow the user guide instructions to create a build directory and pull up the ccmake gui (versions of ccmake and cmake on the PC are 4.0.2 stored in /snap/bin/cmake). Only the IncNavirStokesSolver is on, with USE_MPI switched on with thirdparty builds of GSMPI and SCOTCH. When configuring a cmake warning appears regarding policy CMP0177, and when running 'make install' the following error is displayed: ~~~~ CMake Error at CMakeLists.txt:1 (CMAKE_MINIMUM_REQUIRED): Compatibility with CMake < 3.5 has been removed from CMake. Update the VERSION argument <min> value. Or, use the <min>...<max> syntax to tell CMake that the project requires at least <min> but has been updated to work with policies introduced by <max> or earlier. Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway. -- Configuring incomplete, errors occurred! make[2]: *** [CMakeFiles/gsmpi-1.2.1_2.dir/build.make:92: ThirdParty/stamp/gsmpi-1.2.1_2-configure] Error 1 make[1]: *** [CMakeFiles/Makefile2:1405: CMakeFiles/gsmpi-1.2.1_2.dir/all] Error 2 make: *** [Makefile:146: all] Error 2 ~~~~ I assume it is an error with gsmpi, however when trying to configure with MPI on without building thirdparty GSMPI, the configuring crashes stating it must be built. Any advice is most welcome. Kind regards, Aidan -------------------------------------------------------------------------------------------------- Aidan Forknall Research Associate - Computational Fluid Dynamics of Spray Combustion Rolls-Royce UTC in Combustion System Aerothermal Processes Department of Aeronautical and Automotive Engineering Loughborough University LE11 3TU, UK --------------------------------------------------------------------------------------------------

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No such module: NekFFTW
by ztdepyahoo 04 Jun '25

04 Jun '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* I use IncNavierStokesSolver to solve the channel flow. but it feedback me with "No such module: NekFFTW" I have compiled nektar with fftw support. why did i get this error. | | ztdepyahoo | | ztdepyahoo(a)163.com |

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Time-series of Reynold stresses
by Wang Boning 30 May '25

30 May '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear Nektar++ team, I'm trying to obtain a time series of Reynolds stress. Is there any way to obtain a time series of field-averaged Reynolds stress, or even just at a few specific points? I am currently working with Nektar++ version 5.6.0. However, I am also interested in solutions available in the latest version. I've attempted the following two methods: 1. I tried using the 'history point' filter, but it only outputs variables defined in my session.xml file, specifically uvwp. Is Reynolds stress a predefined variable in Nektar++? Is it possible to define custom variables, such as u'v'? 2. I also tried outputting averaged fields at a high frequency and then post-processing them into a time series. However, this approach leads to enormous disk space occupation, exceeding my authorized storage limit. Is there a more elegant or efficient way to achieve my goal? Best regards, Boning P.S I'm current working on Nektar++ 5.6.0, but I'd like to know solutions for latest version, if there is any.

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Cylinder-Base terminal error question
by 🌸那慢慢🌸 22 May '25

22 May '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear nektar++ users and developers, I am using the base in the flow-stability-cylinder for calculations, and I want to accelerate the appearance of vortices by setting the initial conditions to (1, 0.2, 0). However, the pressure error in the final results is very large, and the filter does not output a file. I would like to know why this is happening. XML file attachment. Hongtao

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Nektar++ Workshop 2025
by Chris Cantwell 21 May '25

21 May '25

Dear all, This year's Nektar++ Workshop will be held on the 24th-26th June 2025 at Imperial College London. We are pleased to announce that Tzanio Kolev (leader of the MFEM project) has agreed to give a keynote lecture at the workshop. More information will be made available via the website soon, including how to register. As with recent years, the event is primarily an in-person meeting, but we will aim to allow the talks to be viewed remotely for those unable to travel. Kind regards, Chris -- Chris Cantwell Reader in Computational Engineering Director of Postgraduate Studies (PhD) Department of Aeronautics Imperial College London South Kensington Campus London SW7 2AZ Tel: +44 (0)20 759 45050 Email: c.cantwell(a)imperial.ac.uk www.imperial.ac.uk/people/c.cantwell

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Nek5000 to Nektar++ Conversion Problem
by 王兴益 13 May '25

13 May '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear nektar-users, I am currently working on converting a flow field from Nek5000 to Nektar++ using the FieldConvert utility. Specifically, I used the following command: FieldConvert input.fld output.fld However, it seems to me that the default conversion cannot take different options of points styles into account. When a xml file is included in the command： FieldConvert example.xml input.fld output.fld Although the output.fld file appears to have the correct SHAPE and BASIS settings, the resulting field data still differs significantly from the original Nek5000 solution. On the other hand, even though I manually ensured that the polynomial order settings are consistent between the two formats and that the POINTSTYPE is set to GaussLobattoLegendre, the resulting output.fld file does not appear to fully or accurately reflect the original Nek5000 field data. Some components seem to be missing or incorrectly mapped. I would appreciate any guidance or suggestions you might have on ensuring a more complete and accurate conversion. Are there any known limitations, specific configuration requirements, or pre-processing steps for converting Nek5000 fields to Nektar++ format? Thank you very much for your time and support. Many thanks, Xingyi Wang Harbin Institute of Technology

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Load time-dependent parameter from outside file
by Chen, Qifan 05 May '25

05 May '25

******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear all, I'm currently working on solving a PDE where a source term which evolves over time. That time dependent parameter cannot be described by a simple function that can be input into .xml; instead, the values can only provided in an external text file. To do it, I can restart Nektar++ with a modified XML file and updated parameters for each time step, but it is very time-consuming due to the initialization of Nektar++. I was wondering if there's a more efficient way to load this time-dependent parameter directly from the external file during the simulation. The methods to load files I find in manual book is not time dependent. Ideally, I'm looking for a method where Nektar++ can load the time-series from the outside file for a parameter. I also wonder the format of such files. Any insights or suggestions you might have on how to achieve this would be greatly appreciated. Thank you for your time and assistance. Best, Qifan

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