Scalar and outlet problem

[Mike Good]

Hello Nek,

I am simulating a simple channel that flows over a rough bed. My simulation diverges when the injected scalar in the channel reaches the outlet. How can I solve this issue?

How can I apply the sponge or other method to my problem?

Thanks
Mike

[Ricardo]

Hi Neks, I also have a problem with the outflow divergence for the scalar field.
I wonder if anyone knows how to extend the velocity sponge zone to multiple scalar fields, or perhaps if anyone knows of a reference work for such a numerical technique.

Ricardo

[Fischer, Paul]

calling turb_outflow in userchk() generally works for channel/pipe flows

---both for scalars and velocity.  It's not great for boundary-layer flows

but often can work with some minor effort.  

From the navier5.f source code:

c-----------------------------------------------------------------------

      subroutine turb_outflow(d,m1,rq,uin)

c     . Set div U > 0 in elements with 'O  ' bc.

c

c     . rq is nominally the ratio of Qout/Qin and is typically 1.5

c

c     . uin is normally zero, unless your flow is zero everywhere

c

c     . d and m1 are work arrays of size (lx1,ly1,lz1,lelt), assumed persistant

c

c     This routine may or may not work with multiple outlets --- it has

c     not been tested for this case.

c

c

c     TYPICAL USAGE -- ADD THESE LINES TO userchk() in your .usr file:

c                      (uncommented)

c

c     common /myoutflow/ d(lx1,ly1,lz1,lelt),m1(lx1*ly1*lz1,lelt)

c     real m1

c     rq  = 2.

c     uin = 0.

c     call turb_outflow(d,m1,rq,uin)

c

ref. is here:

Computer methods in applied mechanics and engineering 196 (31-32), 3049-3060

hth,

Paul

---

From: nek...@googlegroups.com <nek...@googlegroups.com> on behalf of Ricardo <rasf...@gmail.com>
Sent: Wednesday, October 26, 2022 2:20 PM
To: Nek5000 <nek...@googlegroups.com>
Subject: [nek5000] Re: Scalar and outlet problem

 

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[Ricardo]

Hello Paul,

Thank you for your quick reply.

Indeed, it seems to be a great solution. Unfortunately, in all cases where I add these lines, the code crashes at the first time step.

Is there any way to check the routine? Am I missing something else?

Thank you for your time,
R

[Fischer, Paul]

What is the size of your domain and the magnitude of the velocity?

There may be a scaling issue (though I tried to make it scale independent)

---

From: nek...@googlegroups.com <nek...@googlegroups.com> on behalf of Ricardo <rasf...@gmail.com>

Sent: Thursday, October 27, 2022 1:38 PM
To: Nek5000 <nek...@googlegroups.com>
Subject: Re: [nek5000] Re: Scalar and outlet problem

 

To view this discussion on the web visit https://groups.google.com/d/msgid/nek5000/ea6d6e4b-1173-4f71-91bc-57f54a0495e1n%40googlegroups.com.