May 2024 - Nektar-users - imperial.ac.uk

PowerKernel for not available along homogeneous directions?
by Alexander Schukmann 12 May '24

12 May '24

******************* 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 everybody, I am currently running Quasi-3D CG-SVV iLES with the IncNavierStokesSolver and noticed that the SVV PowerKernel is not activated/available for Fourier discretizations along homogeneous directions. However in the paper "Industry-relevant ILES of a high-performance road car via S/HPEM" (Mengaldo et al. 2021) it says: "The current best practice in Nektar has been to use the "DG" kernel in general while employin the "power-law" kenel only along homogeneous directions in case periodic boundary conditions are present" So does this mean the PowerKernel is only available if S/HP is also used along homogeneous directions? Why not use the DGKernel then? And how does one setup different SVV kernels for different spatial directions? If it DOES refer to the quasi-3D case, however, there seems to be an issue, since no output is given regarding SVV, if the "SpectralVanishingViscosityHomo1D" flag is set to "PowerKernel" within the session file. Also I noticed that it seems to be impossible to activate SVV only for the S/HP discretizations in quasi-3D cases, i.e. without using SVV for the Homo1D directions, but vice versa it works. All the best Alex Sicher versendet mit [Proton Mail](https://proton.me/).

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Global vs local polynomial de-aliasing
by Alexander Schukmann 12 May '24

12 May '24

******************* 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 everybody, I have a quick question regarding the "SPECTRALHPDEALIASING" flag for the IcnNavierStokesSolver within the "SOLVERINFO" tag of the session file. Does this activate local de-aliasing only, i.e. de-aliasing with respect to the nonlinear convection term or are other parts of the equation (mass matrix, diffusive flux etc.) also "overintegrated"? Thanks and all the best Alex Sicher versendet mit [Proton Mail](https://proton.me/).

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Taylor Hood approximation causing divergence
by Alexander Schukmann 11 May '24

11 May '24

******************* 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 everybody, I am currently working on a CG-SVV iLES of a cylinder flow at ReD = 3900 with the IcnNavierStokesSolver and wanted to run some 2D tests first, in order to find an appropriate polynomial order for the wall shear stress to converge in a cheap fassion, as suggested by Guglielmo in another post. I read that for under-resolved simulations it can be beneficial to resort to an equivalent of the Taylor Hood approximation and use a polynomial order for pressure that is reduced by 1 compared to velocity. However, the simulation immediately crashes, if "SPECTRALHPDEALIASING" is activated. If however I define the number of quadrature points manually within the "EXPANSIONS" tag to be at least equal to the amount needed to achieve consistent integration of quadratic nonlinearities or higher, the simulations remain stable. I assume by setting the number of quadrature points like this, global de-aliasing is performed, i.e. all the equation terms are overintegrated, instead of only the convective term being consistently integrated. Whereas by activating "SPECTRALHPDEALIASING" local de-aliasing is performed. Has anybody observed this kind of behavior and has an explanation? The simulation remains stable with "SPECTRALHPDEALIASING" switched on, if I rely on P_pressure = P_velocity for the polynomial order. Thanks and all the best Alex Sicher versendet mit [Proton Mail](https://proton.me/).

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CFD to CAA coupling issue
by dauood Tariq 11 May '24

11 May '24

******************* 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 been attempting to use the cwipi function to form a coupled process with the nektar++ incompressible navier stokes solver and the acoustic solver however there is a repeated error that states: Fatal : Level 0 assertion violation Need to set up pressure field definition I am unsure what this means and why it is occuring. Any help would be greatly appreciated Kind regards, Dauood Tariq

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Cwipi coupling not working
by dauood Tariq 08 May '24

08 May '24

******************* 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 attempting to run a cwipi coupling of the APE acoustic and incompressible navier stokes solver however they are not running correctly. The NS solver is sending out velocity files to the APE solver and is running correctly however the APE solver is meant to be reading files but cannot find a the file I have named despite it being done correctly. Any help would be appreciated. Regards, Dauood Tariq

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