CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Special Topics > Visualization & Post-Processing

Interpreting streamlines of a rotating fan.

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 6, 2014, 19:07
Default Interpreting streamlines of a rotating fan.
  #1
Member
 
dab bence
Join Date: Mar 2013
Posts: 47
Rep Power: 13
danbence is on a distinguished road
I have modelled a rotating fan inside a cylinder. The fan is simulated as stationary in a rotating reference frame. When I view streamlines in the rotating reference frame, I get the familiar flow lines going above and below the airfoil sections as we have seen in text books.

My problem is trying to interpret the streamlines when viewed from the absolute reference frame. I wanted to see how much rotation the fan had imparted to the flow downstream. This is not possible when viewing the rotating reference frame streamlines.

In the absolute reference frame, the streamlines look odd. When I start them from the inlet, they travel down and terminate on the surface of the fan. When I do a reverse streamline from the outlet, they terminate on the underside of the fan.

The absolute vector field looks correct and the streamlines reflect those vectors correctly, but the streamlines are implying that a parcel of air is vanishing at the top surface of the fan blade and appearing on the underside, which is clearly nonsense.

I am questioning whether it is actually valid to visualize streamlines in the absolute reference frame ? The absolute vectors show the velocity of parcels of air at a frozen instant of time with the fan also frozen at that time. Streamlines are a method of viewing the passage of time, seeing how a spec of dust will travel through the time it takes to go from the inlet to the outlet. By viewing the streamlines in an absolute reference frame, I am combining a fan that is frozen and the movement of air over a time period. Is this the reason for the odd looking behaviour?

If it is not sensible to view the streamlines in an absolute reference frame, what should I do ? Create an animation where the fan is rotating ?

Any comments would be appreciated.
danbence is offline   Reply With Quote

Old   April 8, 2014, 10:13
Default
  #2
Member
 
dab bence
Join Date: Mar 2013
Posts: 47
Rep Power: 13
danbence is on a distinguished road
I have attached two images of my simulation to illustrate my description . It is one fan blade with a rotational periodic boundary condition. As you can see, the rotating reference frame streamline is easy to interpret, but the streamlines in the absolute reference frame terminates at the upper surface of the fan blade.
Attached Images
File Type: jpg rotatingframe.jpg (91.1 KB, 35 views)
File Type: jpg nonrotating.jpg (91.0 KB, 24 views)
danbence is offline   Reply With Quote

Reply

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
Rotating blades of a fan by Fluent? guillaume1990 FLUENT 17 June 22, 2016 03:01
Rotating blades of a fan Fluent? guillaume1990 ANSYS 1 March 21, 2014 03:15
fan rotating tongnan FLUENT 1 February 7, 2013 16:50
Boundary conditions for rotating fan rohit Siemens 3 October 4, 2008 04:18
axial flow in counter rotating ducted fan Vishu FLUENT 4 January 13, 2004 17:52


All times are GMT -4. The time now is 09:48.