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

Calculating torque

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 21, 2007, 12:17
Default Calculating torque
  #1
Andrew
Guest
 
Posts: n/a
I am running a simulation of a rotor, with constant cross section in the axial direction (see:http://www.andrewgarrard.co.uk/rotor.jpg), rotating in air. I would like to use fluent to calculate the power required to turn the rotor at a give angular velocity. For this, I would need to know the required torque. Is there a method for predicting this with Fluent? I have been looking at using the Report -> Forces... -> moments option but I cannot find a way of calculating the moment from the axis, rather than a fixed point.

Any help, as always, appreciated.
  Reply With Quote

Old   August 21, 2007, 14:05
Default Re: Calculating torque
  #2
Joe
Guest
 
Posts: n/a
Simply transform the moment from the default coord sys to one that you are interested in.
  Reply With Quote

Old   August 21, 2007, 16:04
Default Re: Calculating torque
  #3
andrew
Guest
 
Posts: n/a
Joe, thanks for your help on this matter. Please excuse my ignorance as I am having a little trouble understanding how to implement what you suggest.

When I open the forces on boundaries panel, in order to calculate the pressure moment, I have to supply a force orign ("B" in the manual, section 29.3.1). The origin is specified as a single, fixed point with an x, y, and z value.

I am looking for the torque that would be experienced about the axis of my rotor, in my case the z axis. How do get fluent to ignore the third dimension in the specification of the force centre?

regards,
  Reply With Quote

Old   August 22, 2007, 03:12
Default Re: Calculating torque
  #4
carno
Guest
 
Posts: n/a
I have not yet understood the problem yet, buttry this command on TUI of Fluent 6.3.26.

First find the zone name for rotor wall of interest. The use below command.

>report forces wm n

!* it will ask for the zones, give the zone name (say rotor)*!

rotor

!*It will ask for the centre of rotation. In your case z co-ordinate will be zero.*!

you will get the moment acros the z axis for the supplied wall BC (rotor)

Hope this helps. Same can be done with GUI also.
  Reply With Quote

Old   August 22, 2007, 07:27
Default Re: Calculating torque
  #5
andrew
Guest
 
Posts: n/a
I suppose the problem that I am trying to resolve it this: Say, for example, the image of the rotor I have previously linked to is axisymmetric around the z axis, running from 0,0,0 to 0,0,100. When fluent calculates the total moment vector around A (in manual sec 29.3.1) it uses the moment vector r_AB. r_AB will be calculated based on the distance between specified moment centre (A), and the face that is being used to calculated the pressure force vector (B). If A is specified as 0,0,0 then the faces at the top of the rotor (with larger z value) will have a larger value of r_AB and hence a larger contribution to moment than the faces lower down (with lower z value).

For example, the force on a face near 0,0,0 may have a force of 10 N on it. Another face near 0,0,100 may have the same x and y values as the first and also a torque of 10 N. However, the moment about A (0,0,0) for the second point will be larger than that of the first, as r_AB will be larger for the second. Similarly, if the moment A were taking about 100,0,0, the first face would have a larger moment than the second. As these two points are equally spaced from the z axis, they should contribute equally to the torque on the rotor, regardless of the position taken as the moment centre.

In summary, I would like to be able to specify a moment centre around the axis, rather than a point.

  Reply With Quote

Old   September 4, 2007, 12:10
Default techinical information
  #6
nayan.mathur
Guest
 
Posts: n/a
sir , hi i wanated to know each detailing formulas conserned with torque & what is it
  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
Calculating Torque tripa58 CFX 1 October 28, 2010 19:10
Calculating torque beejois FLUENT 2 March 12, 2010 02:22
calculating torque shawn123 STAR-CCM+ 3 January 23, 2010 22:32
turbine torque calculating in Fluent Bagus Putra Muljadi FLUENT 0 May 18, 2006 03:34
How to update polyPatchbs localPoints liu OpenFOAM Running, Solving & CFD 6 December 30, 2005 18:27


All times are GMT -4. The time now is 18:22.