|
[Sponsors] |
A problem of incorrect fluid flow field using Openfoam |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
June 7, 2017, 01:08 |
A problem of incorrect fluid flow field using Openfoam
|
#1 |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Dear all,
I'm a new Foamer, and currently learning how to use it. And now I have a very confusing problem. My model is simple, just a planar jet flow. Which is showed in figure 1, the gas inlet flow velocity is higher in the middle, and lower in the sides. But I can only get this correct flow field using icoFoam, when I use other solvers, like pimpleFoam, pisoFoam, reactingparcelfoam, etc., the flow field will be wavering, as is shown in Figure 2. The gravity is zero, and the flow field is wavering from up and down, not just one side. Can anybody tell me why? and how to fix this? I can't just use icoFoam, because it's only for laminar flow, and cant do anything else. Many thanks. Maria Last edited by marialhm; June 7, 2017 at 01:10. Reason: supplement |
|
June 7, 2017, 03:25 |
|
#2 |
Senior Member
Gerhard Holzinger
Join Date: Feb 2012
Location: Austria
Posts: 342
Rep Power: 28 |
This is likely due to an interaction of the jet and the walls. If you want to simulate a free jet, consider making the domain wider. You could also compare the results of pimpleFoam, when using a RAS-type turbulence model and an LES-type turbulence model.
|
|
June 7, 2017, 10:28 |
|
#3 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
The second result seems to be unplausible, but it is realistic. If a wall comes near a flow, the wall creates some kind of suctions which moves the flow toward the wall. A tiny irregularity starts that process.
__________________
Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
|
June 7, 2017, 23:21 |
|
#4 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
|
||
June 7, 2017, 23:22 |
|
#5 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
Maria |
||
June 7, 2017, 23:51 |
|
#6 |
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 1,288
Rep Power: 34 |
||
June 7, 2017, 23:57 |
|
#7 |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
||
June 8, 2017, 01:46 |
|
#8 |
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 1,288
Rep Power: 34 |
PISO is not pressure interpolation. It seems you did not make any changes to it, so that means you have standard pressure interpolation if it was old version of fluent and second order central if it is new fluent. The pressure interpolation differences could cause what you are seeing. |
|
June 8, 2017, 05:30 |
|
#9 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
|
||
June 8, 2017, 08:46 |
|
#10 |
Senior Member
|
Hi all,
@marialhm I think it would be MUCH easier if you disclose your geometry, mesh, boundary conditions, schemes, linear solvers, convergence criteria used. Right now, people are trying to explain why the second picture is possible, while simpler answer could be: "your simulation does not converge". And for icoFoam it could be just lucky coincidence. |
|
June 8, 2017, 09:23 |
|
#11 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
Regards, Maria |
||
June 8, 2017, 09:25 |
|
#12 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
|
||
June 8, 2017, 09:57 |
|
#13 |
Senior Member
|
You have hidden the most interesting thing: PIMPLE dictionary in fvSolutions (can't you just post gzipped files?). Also boundary conditions are missing or should we assume, you use "standard" ones?.
|
|
June 8, 2017, 10:05 |
|
#14 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
nNonOrthogonalCorrectors 0; nCorrectors 2; Boundary conditions for U is in figure 3. For P, it's fixed value in outlet, and others are zeroGradient. Acturally I tried several cases, different cases may have small differences. but almost all of them have wavering flow field. Thanks again. Maria |
||
June 8, 2017, 10:13 |
|
#15 |
Senior Member
|
So, basically, you do not check convergence, use GAMG solver and limitedLinear scheme. Do you adjust time step? What is your Courant number? Did you try with PCG instead of GAMG? Did you try to check for convergence (using residualControl)? Did you try other discretisation schemes?
|
|
June 8, 2017, 10:21 |
|
#16 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
|
||
June 8, 2017, 10:31 |
|
#17 |
Senior Member
|
Maybe you could also post domain sizes? So people can at least try to reproduce your behaviour.
I do not believe single GAMG -> PCG change will solve your problem. Though it can postpone start of the oscillations (like it does in case of von Karman vortex street). |
|
June 8, 2017, 10:34 |
|
#18 | |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Quote:
x length: 2m y:0.45m injection width: 0.01m Thanks. Last edited by marialhm; June 8, 2017 at 10:34. Reason: wrong information |
||
June 8, 2017, 23:54 |
|
#19 |
Member
Maria
Join Date: Jul 2013
Posts: 84
Rep Power: 13 |
Hi all,
I think it's not the problem of settings, but it's the reality. @Uwe Pilz is right. But the problem is, how can I set up to avoid this phenomenon? I tried outlet boundaries for the bottom and top, but the results are still not satisfactory. Thanks in advance. Maria |
|
June 9, 2017, 06:24 |
|
#20 |
New Member
Diego Ferrando
Join Date: Mar 2017
Location: Zaragoza
Posts: 19
Rep Power: 9 |
You could try with symmetry boundary condition.
|
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Setting time varying flow field in OpenFOAM | Tings_ | OpenFOAM Pre-Processing | 5 | May 8, 2017 11:21 |
OpenFOAM v3.0+ ?? | SBusch | OpenFOAM | 22 | December 26, 2016 15:24 |
Fluid Flow over a bus -- Convergence Problem | Roberto J. | STAR-CCM+ | 2 | May 12, 2016 14:05 |
Problem with an old Simulation | FrankW | CFX | 3 | February 8, 2016 05:28 |
Problem with rhoSimpleFoam | matteo_gautero | OpenFOAM Running, Solving & CFD | 0 | February 28, 2008 07:51 |