|
[Sponsors] |
Problem with grid convergence for turbulent flow around cylinder |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
November 7, 2018, 06:23 |
Problem with grid convergence for turbulent flow around cylinder
|
#1 |
Member
A
Join Date: Jun 2016
Posts: 30
Rep Power: 10 |
Dear OpenFOAMers,
I have trying to achieve grid convergence for the mean drag coefficient and RMS of the lit force coefficient on a stationary, fixed cylinder at Re = 3.6*10^6. Yet, it seems that the drag and lift force coefficient keep on increasing with relatively big jumps with every mesh refinement. I have used the following meshes: 1. Coarse mesh: N = 69.069 2. Regular mesh: N = 98.730 3. Fine Mesh: N = 176.635 All the meshes were done in 100Dx100D domain. The mesh was divided into multiple blocks, where the cylinder was surrounded by the typical O-grid block. The turbulence model that I am using is k-w SST without wall models. Y+ was smaller than 1 and equal in all three meshes. I have seen in literature another numerical study (title: Numerical simulation of flow around a smooth circular cylinder at very high Reynolds numbers. M. Ong et al., 2009) where grid convergence was reached for a 2D stationary cylinder at Re =3.6*10^6 with approx. N = 50.000. Yet, the paper I am referring to used the k-epsilon model with wall functions and they used a smaller domain. I have also worked with smaller computational domains, however, this did not necessarily lead to different results compared to the larger domains (esp. because I kept the topology of the mesh the same). Personally, I think the meshes I have created are fine and should produce GC. I have uploaded the mesh topology of the fine mesh as a screenshot in the attachment. The regular and coarse mesh have the same topology, yet the amount of cells allocated to the all the edges are decreased with a factor of 1.25. Btw; I created the mesh in ANSYS ICEM and converted it with the utility fluentMeshToFoam (which seemed to work). A summary of my Mesh properties/CFD settings: - Flow is resolved in 2D - Re = 3.6*10^6 - Turb. model: k-w SST without wall function - yPlus < 1 - I use standard BC for a cylinder (Uniform inlet velocity, zero ref. pressure at the outlet, fixedValue of U = (0 0 0) around cylinder wall. - I use a fixed timestep. Al the disc. schemes used are 2nd order. The final residuals have been put on a tolerance of 1e-08. For the p-U coupling I use the PIMPLE family, with 20 outer and 3 inner Correctors and some PIMPLE tolerances. - The case has been run in parallel on four processors. - I know the Courant number in all three cases was well below Co < 0.7 - The case files have been uploaded in the attachment. Things I have tried so far: - I have tried a different mesh topology - I Used less tight PIMPLE settings - I have tried to run with a smaller domain size - I have played a bit with the disc. schemes (tried some 1st order as well) - I tried to use the adjustable timestep scheme as well (Co < 0.7) The problem is that especially the lift coefficient keeps on increasing with big numbers, which makes the grid convergence very hard. I have tried to already run with N = 400.000 cells, but still the lift seemed to go to even higher numbers. It looks like the finer the mesh, the higher the lift force (without reaching a ceiling for grid convergence). I dont believe N>400.000 would be required to achieve grid convergence. Personally, I would think that the meshes are fine (esp. since y+ < 1 and the O-grid is very fine) but there might be a problem with the CFD settings. I am out of ideas at this moment and I am wondering if some of you has faced a similar problem before with achieving grid convergence for a turbulent flow. Please let me know if you have any advice/tips/tricks on this matter. Thanks in advance! And feel free to ask for more information |
|
November 12, 2018, 04:23 |
Bump!
|
#2 |
Member
A
Join Date: Jun 2016
Posts: 30
Rep Power: 10 |
Bump! I am very eager to hear your opinion!
|
|
November 13, 2018, 04:19 |
|
#3 |
Senior Member
Jan
Join Date: Jul 2009
Location: Hamburg
Posts: 140
Rep Power: 20 |
Hi,
have you tried kLowReWallFunction for k and nutLowReWallFunction for nut? No idea, if this helps, but maybe worth to check. Best, Jan |
|
November 13, 2018, 05:39 |
|
#4 | |
Member
A
Join Date: Jun 2016
Posts: 30
Rep Power: 10 |
Quote:
Thanks for your reply. Is maybe not a bad idea, since I am not using a typical wall function for BL prediction but I am resolving up to the viscous sublayer. This could indeed be seen as a 'Low-Re' approach. Thanks! |
||
Tags |
cylinder, grid convergence, grid convergence study, k omega sst, turbulent |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
3D Windturbine simulation in SU2 | k.vimalakanthan | SU2 | 15 | October 12, 2023 06:53 |
Flow past a 2D cylinder - High Re (1E+05) - Cd too high | Pervispasco | OpenFOAM Running, Solving & CFD | 4 | March 14, 2022 03:19 |
Keeping intermediate files | OVS | SU2 | 5 | December 5, 2021 12:41 |
benchmark: flow over a circular cylinder | goodegg | Main CFD Forum | 12 | January 22, 2013 12:47 |
Problem with Convergence at high flow rates | Syed | Siemens | 1 | April 10, 2007 16:18 |