|
[Sponsors] |
October 25, 2010, 13:43 |
Help! Emergency!! Karman Vortex using ANSYS
|
#1 |
New Member
|
Hello everyone.
To begin with, I must say that I am such an idiot ANSYS learner . I've tried hard to simulate Karman Vortex Street with CFX. But now, I get no result at all. Please, anyone that have experienced this before, guide me step by step from the modelling, meshing... But, I found biggest difficulty in meshing. I use ANSYS 12.1 I appreciate your advices much, many thanks to you!!! |
|
October 25, 2010, 19:59 |
|
#2 |
Senior Member
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17 |
Hi -
Nobody is going to give you a step-by-step guide. Capturing the von Karman vortex street is pretty challenging for a new user. You'll need to post specific questions and give details of particular problems. http://www.cfd-online.com/Wiki/Ansys_FAQ |
|
October 26, 2010, 00:09 |
|
#3 |
New Member
|
Oh, thank you very much, Mr. Josh.
My biggest problem is I cannot generate a fine mesh (or suitable mesh) for the simulation. Actually, I learn everything by myself but this Karman Vortex simulation is really challenging as you said. That's why I need help. Do you have any advice for me in meshing for Karman Vortex simulation? |
|
October 26, 2010, 01:51 |
|
#4 |
Senior Member
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17 |
I understand your struggle. I had to learn everything myself, as well.
What meshing program are you using? I'd recommend avoiding CFX's built-in meshing program. Use ICEM (or Gambit), something that can create a nice structured mesh and allows for optimal control. Get a copy of Spalart's "Young-Person's Guide to Detached-Eddy Simulation Grids" (2001). Although it focuses on DES, the grid for the cylinder would be excellent for URANS, as well. Make sure the grid refinement is sufficient in the boundary layer and wake regions. Do this by creating at least three meshes, each doubling in resolution (e.g., mesh 1: 50000 nodes; mesh 2: 100000 nodes; mesh 3: 200000 nodes). Once the desired results (e.g., skin friction) have stopped changing with further refinement, you have obtained a grid-independent solution. Also, ensure the grid quality is sufficient. Cylinder simulations are very common. Search this website. Here's one page about cylinders: http://www.cfd-online.com/Wiki/Flow_...cular_cylinder Make sure the simulation is transient (unsteady). Good luck. |
|
October 26, 2010, 02:28 |
|
#5 |
New Member
|
Many thanks to you. I'll try harder. Anyway, this problem is sure uneasy. Thanks for your advice, I do appreciate that much!
|
|
October 26, 2010, 03:33 |
|
#6 |
Senior Member
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17 |
You're welcome! Let us know what you figure out.
|
|
October 28, 2010, 08:37 |
|
#7 |
New Member
Amir Khodabandeh
Join Date: Oct 2010
Location: Sweden
Posts: 10
Rep Power: 15 |
the most important part is (as josh mentioned): Make sure the simulation is transient (unsteady).!!!
this, what I waste lots of time to figure that out! also I believe if u do it for urself the mesh would not be much difficult maybe even a 2d can do the trick! |
|
November 10, 2010, 11:50 |
|
#8 |
New Member
|
Thank you all. I finally solved the problem. I made a mesh of ~420.000 nodes, after 8 hours running the simulation on a Core i3-330 laptop, I got the Karman Vortex Street. SO HAPPY!!!
|
|
November 10, 2010, 14:31 |
|
#9 |
Senior Member
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17 |
Congrats. A video would be great. If you're feeling generous, you can describe your setup in greater detail (e.g., unstructured/structured mesh, boundary layer resolution, Reynolds number, timestep size, discretization scheme...)
|
|
November 11, 2010, 15:01 |
|
#10 |
Member
Fabian E.
Join Date: Nov 2009
Posts: 38
Rep Power: 16 |
I did a transient simulation in CFX. I used an unstructured "2D" Mesh generated with ICEM. In fact it was no big deal to get the desired result. The key point was a sufficient small time step. I estimate this by the seperation frequency which can be calculated by the strouhal correlation for several bodies.
example: http://www.youtube.com/watch?v=TGNQL0WCVDo |
|
November 11, 2010, 16:39 |
|
#11 |
New Member
Amir Khodabandeh
Join Date: Oct 2010
Location: Sweden
Posts: 10
Rep Power: 15 |
I cr8 group on fb CFD(wonder y no one else build it before me) and 1 of the members post 2 interesting video
http://www.facebook.com/pages/CFD/173392319338461 I am lazy to grab links from youtube and post it separately! |
|
November 12, 2010, 02:34 |
|
#12 | |
New Member
|
Quote:
|
||
November 28, 2010, 02:21 |
|
#13 |
New Member
|
Everyone, thank you a lot for helping me out. After many runs, I finally relatively satisfied with this video of my simulation.
Please take a look and give me advice for better development. I appreciate much. http://www.youtube.com/watch?v=bfF2Ktn5oQA |
|
November 28, 2010, 05:41 |
|
#14 |
New Member
Amir Khodabandeh
Join Date: Oct 2010
Location: Sweden
Posts: 10
Rep Power: 15 |
congrats.
I think it is just ok and fine! |
|
November 29, 2010, 02:51 |
|
#15 |
Senior Member
Joshua Counsil
Join Date: Jul 2009
Location: Halifax, Nova Scotia, Canada
Posts: 366
Rep Power: 17 |
Looks good to me. Good job.
|
|
December 6, 2010, 02:02 |
|
#16 |
New Member
|
This is my 2nd simulation and it's a square cylinder:
http://www.youtube.com/watch?v=BFHzHGwL3I8 |
|
Tags |
ansys, cfx, karman, vortex |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
von Karman vortex street. Vortices formation mechanism. | mnvl | Main CFD Forum | 1 | February 24, 2010 17:53 |
low Re (30-170) Karman vortex street | Sponi | FLUENT | 0 | March 16, 2007 13:27 |
Karman vortex street ??? | anisa | FLUENT | 1 | May 5, 2005 13:04 |
Karman vortex street | Zhipeng | FLUENT | 5 | June 24, 2002 11:00 |
Kármán vortex street in cavitating flow behind bodies in the cavitation tunnel | L. Könözsy | Main CFD Forum | 0 | April 17, 2000 13:16 |