******************* 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: <I PROPERTY="Driver" VALUE="ModifiedArnoldi" /> So I suggest the following solver condition: *<I *PROPERTY*=*"SOLVERTYPE" VALUE*=* "VelocityCorrectionScheme"*/>* *<I *PROPERTY*=*"EQTYPE" VALUE*=* "UnsteadyNavierStokes"* />* *<I *PROPERTY*=*"Projection" VALUE*=*"Continuous"* />* *<I *PROPERTY*=*"EvolutionOperator" VALUE*=*"Direct"* />* *<I *PROPERTY*=*"TimeIntegrationMethod" VALUE*=*"IMEXOrder3"* />* *<I *PROPERTY*=*"Driver" VALUE*=*"ModifiedArnoldi"* />* *<I *PROPERTY*=*"HOMOGENEOUS" VALUE*=*"1D"*/>* *<I *PROPERTY*=*"ModeType" VALUE*=*"HalfMode"*/>* and the following parameter condition: *<P>* kdim = 16 *</P>* *<P>* nvec = 1 *</P>* *<P>* nits = 500 *</P>* *<P>* evtol = 1e-06 *</P>* *<P>* HomModesZ = 1 *</P>* *<P>* BETA = 1.0 *</P>* *<P>* LZ = (2*PI)/BETA *</P>* Best regards, Abhishek On Sun, Aug 31, 2025 at 6:15 PM Gaurav Gupta <gauravxpgupta@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