Hi Ehsan That is rather unusual behaviour. The only thing I can think of is that the solution has locked due to an inf-sup type condition. I have mainly however seen this at higher Re. Anyway you could try running the pressure at a NumModes which is one order lower than the velocity but you have to use the same quadrature order. There are details in the user guide how to do this (search for Taylor Hood). This expansion setup satisfies the inf-sup condition. Cheers, Spencer. From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of Ehsan Asgari <eh.asgari@gmail.com> Date: Saturday, 15 April 2023 at 15:42 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] unphysical flow field with higher polynomial order This email from eh.asgari@gmail.com 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, When I increase the polynomial order from 5 to 6, the flow field becomes unphysical. It reaches a frozen state in which the solution does not change with time anymore! I have provided two planar snapshots of the flow fields for p=5 (first) and p=6 (second) below: [cid:ii_lgi2y4s10] [cid:ii_lgi2yuqi1] As you can see in the images above, p=6 resulted in a weird wake pattern (frozen in time) which is not physical either. My case is a 3-D low-Re flow and I am using the incompressible solver. I was wondering if something may be wrong with what I am doing, or if there is a specific issue with the numerics. Any help would be appreciated. Kind regards syavash