[Nek5000-users] Pipe with expansion

Sat Jan 18 12:22:27 CST 2014

Kamal,

Have you looked at the peris example?  The usr file there shows how to deform
a pipe geometry.

Paul

________________________________
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: Saturday, January 18, 2014 12:17 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Pipe with expansion

Dear Paul,

I tried many ways to map my straight pipe geometry but it does not seem to work properly

I used something like

X = X + Z * tan ( alpha )
Y = Y + Z* tan (alpha )

even that dint work. could please help me with this

Thank you

Kamal.

On Jan 17, 2014, at 2:24 PM, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:

Hi Paul,

Thanks paul. I tried working with the diverging mesh modification.

I tried to use this form of equation to modify the mesh

z = mx + b
z = ny  + c

x = ( z - b ) / m
y = (z - c)  / n

Do you think would work ? or is there any other way to input that ?

Thanks,

Kamal

On 17/01/2014 14:14, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:
Kamal,

1) To check for convergence, run your simulation for increasing polynomial orders ( lx1 in the SIZE file) and measure some consistent quantity (drag, TKE, etc).  You can plot this quantity against lx1 and this should give you a good picture of how you are converging (without needing to change the physical mesh).

2) If you weren't using temperature in your simulation, you could do put the following code snippet in your userchk

c-------------------------------------------
integer i, ntot

ntot = nx1*ny1*nz1*nelv  ! total number of points in simulation (on THIS processor)

do i = 1,ntot
   t(i,1,1,1,1) = 0.5*(vx(i,1,1,1)**2 + vy(i,1,1,1)**2 + vz(i,1,1,1)**2)
enddo

ifto = .true.
c-------------------------------------------

I've assumed here that your density is unity.  This computed kinetic energy point-wise and stores it in the temperature field.  The part "ifto = .true." tells Nek to output the temperature field whenever it outputs a field file.  You could then view this in visit just like you would the velocity field.

Hope this helps!

Josh

On Wed, Jan 15, 2014 at 9:52 AM, <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>> wrote:
Hi Paul,

I will try that mapping, I created a straight pipe to do some simulations.

1) Is there a way to check my spectral convergence, so that I can do some mesh convergence study?
2) Is there a way to plot the kinetic energy in the flow ?

Thank you,
Kamal

On 15/01/2014 12:14, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:

Hi Kamal,

For the geometry you describe, I would apply mesh morphing
to a standard straight pipe.  You can create such a pipe
using a subset of the mkmesh script provided in the expansion
example.

If your transition region is conical, then I woud make
certain that the change in slope occurs at element boundaries,
i.e., as in the half cross-section depicted below:

                              _______________
                             /|      |      |
                           /  |      |      |
                         /|   |      |      |
       ________________/  |   |      |      |
       |     |     |   |  |   |      |      |
       |     |     |   |  |   |      |      |
       +-----+-----+---+--+---+------+------+---->  z

Paul

On Wed, 15 Jan 2014, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:

Hi Paul,

I looked at the example and it looks very helpful, but for a sudden expansion we have only two parts (i.e) the inlet pipe and the outlet pipe. Whereas in a diverging pipe we have three section (i.e,) The inlet pipe, Diverging section and the outlet pipe.

Is it possible for me to create a 2D diverging section using mesh modification and revolve it around the centre axis to get a 3d diverging pipe ?

or should I apply the mesh modification directly to the 3d sudden expansion pipe using usrdat2() ?

Thanks,
Kamal

On 14/01/2014 21:09, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:
Hi Paul,

Thanks a lot for the update. I will take a look at as soon as possible and keep you updated with it.

Thank you,

Kamal

On Jan 14, 2014, at 9:04 PM, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:

Kamal,

I've added an example for a step-type expansion in a pipe. New example directory
is nek5_svn/examples/expansion, with a README.

If you want a standard diffuser, I would use mesh-morphing, as outlined in the
nek primer, which can be found on this page:

http://nek5000.mcs.anl.gov/index.php/UG#Documentation

I've also automated our turbulent outflow bc treatment -- one simply provides an
expansion factor (typically ~ 1.5) and two persistent arrays to turb_outflow(), which
is now in navier5.f.    This can be useful when very strong vortices are leaving the
domain, which is possible for certain diffuser flow conditions (and others).

Paul
________________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov<mailto:nek5000-users-bounces at lists.mcs.anl.gov> [nek5000-users-bounces at lists.mcs.anl.gov<mailto:nek5000-users-bounces at lists.mcs.anl.gov>] on behalf of nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> [nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>]
Sent: Monday, January 13, 2014 3:35 AM
To: nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>
Subject: [Nek5000-users] Creating a Mesh

Hi

Can some one please help me in this because I am new to nek

1) How can I create a .rea for a specific geometry say ' A sudden
expansion pipe ' or a ' Diverging pipe '

2) What tool I should use to create that mesh.

Thank you

kamal
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--
Josh Camp

"All that is necessary for the triumph of evil is that good men do nothing" -- Edmund Burke

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