- Nektar-users - imperial.ac.uk

Questions Regarding Eigenvalue Computation in Stability Analysis
by shan xiangjun 01 May '25

01 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 Prof, I hope this message finds you well. I am currently conducting a Floquet analysis and using the ModifiedArnoldi method to compute the leading eigenvalues. When the parameter beta is small, the computation converges and produces reasonable results. However, when beta becomes large, all computed maximum eigenvalues turn out to be 1. Increasing the nvec parameter makes it difficult for the calculation to converge. I also tried using the Arpack option and obtained the same results. Could you please advise on how to resolve this issue? Additionally, I would like to inquire about the application scenarios for the BaseFlow_interporder parameter. Can it be used in stability analyses for non-periodic problems? Thank you very much for your time and support. I look forward to your guidance. Best regards, Xiangjun Shan

3 7

Questions about the units of the parameters set in Nektar++.
by Luqi Zhang 08 Apr '25

08 Apr '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 apologize for disturbing you again. I'm currently having trouble setting the kinvis value and noticed that the Nektar++ User-guide sets it to <kinvis=1/Re>. Does this mean that when defining parameters in <PARAMETERS>, they need to be dimensionless , such as timestep, kinvis. If so, how do I define the reference velocity and length in Session.xml for doing dimensionless? Or are they just default values? Moreover, should u,v,p in <BOUNDARYCONDITIONS> and <InitialConditions> be dimensionless, as well? Thank you very much for your time and support. I look forward to your response. Best regards, Luqi Zhang

3 2

Missing Metadata in Checkpoint Files After Switching to Checkpoint Filter in Nektar++ 5.3.0
by z 67 05 Apr '25

05 Apr '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 am encountering an issue with checkpoint file metadata when using the <FILTER TYPE="Checkpoint"> configuration in Nektar++ 5.3.0. I would appreciate your guidance to resolve this. Previously, I used global parameters in session.xml (e.g., IO_CheckSteps) to output checkpoint (.chk) files, which correctly included metadata such as <Time>, <TimeStep>, and <ChkFileNum> in the <Provenance> section. However, after switching to the <FILTER> configuration to *delay checkpoint output until 15 seconds* (see configuration below), the generated .chk files now *lack critical metadata*: <FILTER TYPE="Checkpoint"> <PARAM NAME="OutputFile">un</PARAM> <PARAM NAME="OutputFrequency">10000</PARAM> <PARAM NAME="OutputStartTime"> 15 </PARAM> </FILTER> The missing metadata includes: <ChkFileNum> <Kinvis>1.4<SessionName0><Time><TimeStep> This causes .dat files converted via FieldConvertto *lack SOLUTIONTIME*, preventing time-series visualization in Tecplot. So I just have few questions below: 1. Is there an error in the <FILTER> configuration that causes metadata omission? 2. Are there additional parameters required to preserve <Time>, <TimeStep>, etc., when using the Checkpoint filter, which can solve this problem. 3. Is this a known issue in Nektar++ 5.3.0? Thank you in advance for your assistance. Best regards, Luqi Zhang

2 1

Value of δ in HOutflow condition
by Isaac Rosin 31 Mar '25

31 Mar '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. ******************* Hello Nektar++ Community, I am using the HOutflow condition at the outlet of my flow domain with the incompressible Navier-Stokes solver. According to the user guide, this is enforcing a boundary condition defined by Dong, Karniadakis and Chryssostomidis in equation 3 of their paper: A robust and accurate outflow boundary condition for incompressible flow simulations on severely-truncated unbounded domains. This boundary condition is also stated in equations 11.27 and 11.28 of the user guide. Both the paper and the user guide state that δ is "chosen to be sufficiently small" without explaining what constitutes sufficiently small. Would anyone happen to know what value of δ is used by Nektar++ or where I could find it? Kind regards, Isaac

2 2

nektar for dynamic stall simulations
by Lars Wein 31 Mar '25

31 Mar '25

Dear Nektar-Team, last week during the ETC conference in Hannover, I listend to Mr. Spencer. I think he mentioned you are currently working on a methodology to simulate moving bodies. In my team, we are simulating dynamic stall on wind energy turbines, using openFOAM and a sliding mesh interface. The blade performs an oscillating pitching motion, defined by the user (not two-way FSI). Since we strive for hybrid RANS LES, or even wall resolved LES, I would prefer to switch from openFOAM to a solver that supports higher order numerical methods. Do you think Nektar would be feasible for this kind of simulations? Best regards Lars Wein -- Dr.-Ing. Lars WEIN <https://www.tfd.uni-hannover.de/de/institut/unser-team>Team Leader Multiphysics of Turbulent Flows & Deputy COO Logo LUH / TFD Gottfried Wilhelm Leibniz Universität Hannover Institute of Turbomachinery and Fluid Dynamics | TFD An der Universität 1 Geb. 8140, Raum 209 30823 Garbsen, Germany Telefon: +49 (0)511 762 2347 Fax: +49 (0)511 762 3997 E-Mail: wein(a)tfd.uni-hannover.de Web: www.tfd.uni-hannover.de <http://www.tfd.uni-hannover.de>

2 2

Time derivatives
by Guillermo Suárez 16 Mar '25

16 Mar '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. ******************* Hello, Is there a way to write the time derivatives of velocity and pressure to a file, possibly using FieldConvert? I am specifically interested in the incompressible solver. Thank you. Cheers, Guillermo

2 1

pipe flow tutorial
by 秦志文 03 Mar '25

03 Mar '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 am using naktar++ 5.3.0 for research and have seen the example of 'turbulent pipe flow' in the user guide, but I cannot find it in the installation package. Could you please provide it. regards ZhiWen Qin

2 1

C0Projection module
by Gao 24 Feb '25

24 Feb '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. ******************* Hello, I have much discontinuous (across element interface) distribution of variable in the fluid field. Why this happened? Then I want to use C0Projection module to smooth the fluid field. My mesh is third order, but the error comes ou below, and the other module of FieldConvert works. Fatal : Level 0 assertion violation Variable index out of range. terminate called after throwing an instance of 'Nektar::ErrorUtil::NekError' what(): Level 0 assertion violation Variable index out of range. Could someone give me some advice? With best regards

2 2

how do I get Nektar++
by Igweh Chijioke 11 Feb '25

11 Feb '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. ******************* Sir,I wish to install the software please how can I get it done?IGWEH CHIJIOKE OBIORA.

2 1

Compressible Navier-Stokes Homogenous 1D
by Zhicheng Wang 25 Jan '25

25 Jan '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’m running the compressible flow past a cylinder using the Nektar++ compressible flow solver. So far the implicit time stepping method works well both in 2D and 3D. However, when I try to run 3DHomogenous1D NavierStokesImplicitCFE solver, it gives me error says v_GetLocTraceToTraceMap not coded. I wonder if I have not set the session file correctly or this implicit 1D homogenous solver has not been implemented yet ? Below is solver information, in case I have used the wrong parameters. <SOLVERINFO> . </SOLVERINFO> Best Regards, Zhicheng Wang

2 1