[Nek5000-users] Velocity inlet boundary condition issue

[nek5000-users at lists.mcs.anl.gov]

Hi Toon,

If you also have Walls, then v=0 at the all, and 0.1 at the other grid points.  However, what
you have is a polynomial that is 0 at one point and 0.1 at the others... such a thing will be oscillatory.
(Similar to Gibbs phenomena for Fourier representation of a square wave.)

Usually, we would have a boundary layer that smoothly transitions from a constant down to zero
at the wall.

I usually do this with a polynomial fit that uses a polynomial order = (lx1-1)

Paul

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From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Tuesday, July 26, 2016 2:12 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Velocity inlet boundary condition issue


Dear users,


I have a channel simulation where I set the boundary condition of one of the domain side as 'v' (in the box file). Then in the userbc subroutine, I define the velocity at that boundary as a constant (say 0.1). After I run my simulation and visualise the result, the velocity at that boundary is not exactly the constant I put in the user file. Do you have any idea how this could happen?


Thank you in advance.


Best regards,

Toon

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