CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Asymetric results on a symetric geometry

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree3Likes
  • 1 Post By ghorrocks
  • 1 Post By evcelica
  • 1 Post By Gert-Jan

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 23, 2022, 12:13
Default Asymetric results on a symetric geometry
  #1
RVI
New Member
 
Join Date: Jan 2022
Posts: 2
Rep Power: 0
RVI is on a distinguished road
Hello,
I am pretty new to CFX. I am simulating water passing by some symmetric geometry through a restriction in 3D. Asymmetric simulation can not be used here for further step

As shown in the picture, the turbulences and the flow shape after the restriction is not symmetric.

I don't get to understand if my results are normal. Is it due to my turbulence model (SST)? Does CFX consider the non-linearities? Or, are there other points I am missing out?

I have tried both Hexa and tetra meshes but both end up with (more or less) the same results. Either with the model - tried both with half of it or the full 3D model.

Regarding the convergence criteria, I choose the flow either tend to go right or left. Would an unsteady simulation solve it?

I am pretty lost. If these nonlinear results are normal can someone explain to me why?

Appreciate your time!
VR
Attached Images
File Type: png Capture12.PNG (85.5 KB, 10 views)
File Type: png Capture13.PNG (33.2 KB, 13 views)
RVI is offline   Reply With Quote

Old   June 23, 2022, 20:54
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,234
Rep Power: 135
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
When fluids flow over a symmetric geometry they do not always result in symmetric flows. That is part of the beauty of fluid mechanics. A famous example is the von Karman vortex street, where flow over a cylinder generates a periodic vortex pattern. (https://en.wikipedia.org/wiki/K%C3%A..._vortex_street)

So the effect you are seeing is probably real. The jet will flip to one side, and possible flap about. This means you should do a transient simulation to see which it is.
RVI likes this.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   June 29, 2022, 16:09
Default
  #3
Senior Member
 
Erik
Join Date: Feb 2011
Location: Earth (Land portion)
Posts: 1,116
Rep Power: 21
evcelica is on a distinguished road
What you are seeing is very well known, and called the Coanda effect.
It is caused by the Bernoulli principal (higher velocity = lower pressure). Pressure is lower on the wall where the jet goes since it is traveling faster than the rest of the fluid. This low pressure wall pulls the jet to that side and holds it there. If your pipe were oval, the jet would probably lock to one side, but in a circular pipe, it may wander around the circumference.
RVI likes this.
evcelica is offline   Reply With Quote

Old   July 4, 2022, 04:54
Default
  #4
Senior Member
 
Gert-Jan
Join Date: Oct 2012
Location: Europe
Posts: 1,643
Rep Power: 25
Gert-Jan will become famous soon enough
What question do you want to answer? Do you want to know the flow rate as function of pressure drop? Then your results will be reasonably fine.

But it you want to undertand the flow downstream the nozzle, then this is certainly not a problem to solve using symmetry. Your jet will travel around in all directions. You will need a full transient 3D model to solve this properly.

In this case, you should look in literature for help. Depending on the expansion ratio, the jet in the chamber downstream will behave very differently. You can find this in e.g. Guo, Langrish & Fletcher - Numerical simulation of unsteady turbulent flow in axisymmetric sudden expansions, 574(123), Transactions of the ASME, 2001
RVI likes this.
Gert-Jan is offline   Reply With Quote

Reply

Tags
asymmetric, cfx, restriction, symmetric, water

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Duplicating/pattern results for same geometry but multiple separate instances gopisandy FLUENT 0 June 17, 2019 12:41
how cfd results can be trusted in a very complex geometry garrison Main CFD Forum 1 November 8, 2014 05:13
Comparing Air numerical results with water experimental results cristian2009es Main CFD Forum 1 July 2, 2014 19:11
Problem Importing Geometry ProE to CFX fatb0y CFX 3 January 14, 2012 20:42
[DesignModeler] Error while Loading a Geometry JD944 ANSYS Meshing & Geometry 0 October 25, 2011 15:51


All times are GMT -4. The time now is 18:14.