CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Weird velocity vector shape after step height (BFS)

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 23, 2012, 05:30
Default Weird velocity vector shape after step height (BFS)
  #1
New Member
 
Join Date: Nov 2011
Posts: 24
Rep Power: 5
warlocklw is on a distinguished road
Below is backward-facing step 1 micron microchannel with 75% step height, 500 Reynolds number. Investigation is performed on velocity vector after step height. It appears that something interesting happen.

View 1, 5 pictures (further away from step height)











View 2, 5 pictures, same with View 1 (Further away from step height)











There appears a egg-alike shape after step height, when the recirculation zone is over. Why is this happen? Please help for anyone know. Thank you.
warlocklw is offline   Reply With Quote

Old   May 23, 2012, 06:29
Default
  #2
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,971
Blog Entries: 6
Rep Power: 39
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
this seems to be the projection method problem. Select the proper projection method for plotting vectors.

Or this may be something new. I am not sure.
Far is offline   Reply With Quote

Old   May 23, 2012, 07:23
Default
  #3
New Member
 
Join Date: Nov 2011
Posts: 24
Rep Power: 5
warlocklw is on a distinguished road
Since this is about fluid velocity, I am quite sure it should already been discovered. The projection is view towards outlet, or view towards -z axis. Above views are set so that clear view of what happened can be observed. The flow type is set as laminar flow.

My original assumption is there are 2 forces acting on it. One is fluid kinetic flow at the center, another one is fluid viscosity towards call that drag the fluid. 2 forces acting on different direction, causing the egg shape things.

However, this egg shape not happen before step height. That's why I suspect step height has something to do with the formation of it. Please help, any reply is welcomed and appreciated. I will post any view required.
warlocklw is offline   Reply With Quote

Old   May 24, 2012, 04:39
Default
  #4
New Member
 
Join Date: Nov 2011
Posts: 24
Rep Power: 5
warlocklw is on a distinguished road
I changed arrow shape and discovered that fluid at side flow upwards to fill the void created when the current flow down. The egg shape are vector between vector flow down at center and vector go up at side. This thread can be closed. Thanks for your help.
warlocklw is offline   Reply With Quote

Old   May 24, 2012, 05:22
Default
  #5
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,971
Blog Entries: 6
Rep Power: 39
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
so that was the visualization problem?
Far is offline   Reply With Quote

Old   May 24, 2012, 05:51
Default
  #6
New Member
 
Join Date: Nov 2011
Posts: 24
Rep Power: 5
warlocklw is on a distinguished road
Can be say so, since the fluid near boundary flow at slow speed, the arrow is too small. When I normalized it, I can see the arrow direction clearly. And I notice that the horizontal and vertical line are actually arrowhead. Horizontal means fluid flow up and down, vertical means fluid flow left and right.
warlocklw is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Inlet/initial velocity for fractional step zonexo Main CFD Forum 0 March 31, 2006 03:41
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07
Setup for laminar backward facing step (bfs) quarkz Main CFD Forum 13 September 30, 2005 09:51
Velocity Under-relaxation in SIMPLE type methods Matt U. Main CFD Forum 6 July 4, 2005 05:29
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 09:11


All times are GMT -4. The time now is 19:45.