HI Guglielmo,

Thanks for the feedback. It does look like there is a bug between the composite definition since it would look like not all degrees of freedom are being correctly constrainted. Can you send the mesh file along too so we can see if an ADRsolve  also shows the same issue.

Joao (cc’ed) has been looking at setting up a way to specify different polynomial orders in different regions and so this might be an alternative?

Cheers,

Spencer.

From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of Guillermo Suarez <guillermo180395@gmail.com>
Date: Tuesday, 31 January 2023 at 23:01
To: nektar-users <nektar-users@imperial.ac.uk>
Subject: [Nektar-users] Spurious results using composites with different discretization orders

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Hello,

I want to solve the incompressible flow around the naca0012 with
nektar++. I have attached the input file that I am using for such a
case. For nektar++ versions v5.1.0, v5.2.0 and 5.3.0 (master) some
spurious results, two checkerboard patterns, around half and one chord
length right above the trailing edge show up. Such a checkerboard
pattern does not appear when using nektar++ v5.0.1 and v5.0.2. I have
enclosed a screenshot showing the comparison between the different
versions.

The checkerboard pattern seems to first appear in the horizontal
velocity, u. It develops right at the boundary between two composites
with different discretization orders. This is not the only boundary
between composites with different nummodes. The pattern does not belong
to a transitory state, once it shows up it will not fade or get shed
outside of the domain. It will eventually appear in the pressure and
vertical velocity fields as well, but their magnitudes are considerably
smaller compared to one present in the horizontal velocity.

I have tried different approaches to mitigate it:
- Increase and decrease nummodes.
- SVV
- Diferent precodnitiones for velocity and pressure
- Different Reynolds number
- Differnt operators for SmoothAdvection
- Differnt operators for GlobalSysSoln

The pattern only does not show up when using the same discretization
order for all the composites.

Any help would be welcome.

Cheers,
Guillermo