September 2025 - Nektar-users

Conjugate Heat Transfer Development in Nektar++
by Abhishek Kumar 26 Sep '25

26 Sep '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 would like to know if there is any branch of Nektar++ that includes conjugate heat transfer (CHT) development. From what I can see, this feature does not appear to be included in the current code. I am exploring ways to perform CHT calculations with Nektar++. Could you please let me know if there has been any past development in this area? Best regards, Abhishek Abhishek Kumar CFD/MHD Analyst abhishek.kumar(a)tokamakenergy.co.uk<mailto:abhishek.kumar@tokamakenergy.co.uk> www.tokamakenergy.co.uk<http://www.tokamakenergy.co.uk/> Tokamak Energy Ltd, 173 Brook Drive, Milton Park, Abingdon, OX14 4SD [cid:46e2000d-de1a-4ec1-92e1-5b361360221f] This e-mail and any attachments are confidential and may contain personal views that are not the views of Tokamak Energy Ltd unless specifically stated. If you have received this email in error, please notify the sender immediately and then delete it from your system. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission.

2 2

Validation of Biglobal Floquet Analysis of Cylinder
by Gaurav Gupta 19 Sep '25

19 Sep '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 All ! I am trying to validate the Barkley JFM paper on the Biglobal floquet analysis of cylinder. I am doing the simulations at the following Re and Beta values to find the neutral modes and create a curve of neutral modes (as done in the paper) to identify the critical Re and Beta. 1. Re 190; Beta = 1.4 and 1.8. 2. Re 200, Beta = 1.2 and 2.0 For the above cases, the leading eigenvalue magnitude should be approximately 1. But the solver is producing eigenvalues with magnitude greater than 1. For example, converged eigenvalues for Re=190 and Beta=1.4 Magnitude Angle Growth Frequency EV: 0 1.28858 0.886868 0.202835 0.709494 EV: 1 1.28858 -0.886868 0.202835 -0.709494 EV: 2 1.13585 0.342226 0.101906 0.273781 EV: 3 1.13585 -0.342226 0.101906 -0.273781 For the base flow, I am doing DNS for around 40 shedding periods (~200s) and then storing 32 snapshots for the 41st shedding period. DNS solution is converged and validated against CD, and St values. The DNS mesh has around (~2050 Quads and 7th order polynomial). I also made sure that the 1st snapshot is not equal to the 32nd snapshot as mentioned in the user-guide. Later, I am interpolating the DNS snapshots to a coarser mesh (~550 Quads and 7th order polynomial) using FieldConvert. These interpolated chk files are used as baseflow for the Floquet Analysis. I would be highly grateful, if anyone could help me out with this. I have attached my case setup files for Re=190 and Beta=1.4 case. Case Files: https://drive.google.com/drive/folders/1-0fbs1mxAuQVKfYpbSpj5PBod2aQjKKS?us… Thanks! Regards, *Gaurav Gupta* Scientist/Engineer-SC Space Applications Centre, ISRO Ahmedabad, GJ, India

2 1

Re: [Nektar-users] Problem in Validation of Biglobal Stability Analysis with ARPACK
by Abhishek Kumar 02 Sep '25

02 Sep '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 Gaurav, Thank you for your kind email. I would suggest reducing the Krylov dimension to 16. Since your base flow is 2D2C, you can use HalfMode as the ModeType, which will reduce your computation time. Furthermore, I noticed that for β = 1, you have set Lz = 1, which is incorrect. It should be Lz = (2π)/β. I have also found that ModifiedArnoldi sometimes works better than Arpack: So I suggest the following solver condition: ** ** ** ** ** ** ** ** and the following parameter condition: ** kdim = 16 ** ** nvec = 1 ** ** nits = 500 ** ** evtol = 1e-06 ** ** HomModesZ = 1 ** ** BETA = 1.0 ** ** LZ = (2*PI)/BETA ** Best regards, Abhishek On Sun, Aug 31, 2025 at 6:15 PM Gaurav Gupta <gauravxpgupta(a)gmail.com> wrote: > Hello Prof. Abhishek, > I saw your answers to multiple queries in the NEKTAR++ community and > believe would be help me with stability analysis using NEKTAR++. I am > trying to validate the results of biglobal LSA of NACA0012 at AOA=16 with > ARPACK. I was able to recreate the base-flow and tried to do the direct > analysis with shift invert transformation at 0i, 2i, 4i, 6i, 8i and 10i and > beta=1 but the eigenvalues are not correct. I have attached the case files > as well as the reference paper. I will be highly grateful, if you could > check my implementation and highlight any possible issues. > > Thanks! > > Regards, > *Gaurav Gupta* > Scientist/Engineer-SC > > Space Applications Centre, ISRO > > Ahmedabad, GJ, India >

1 0