[Nek5000-users] Pipe with expansion

Sat Jan 18 12:17:05 CST 2014

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 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 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> 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 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 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 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 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 [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: Monday, January 13, 2014 3:35 AM
>> To: 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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