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.

Simply transform the moment from the default coord sys to one that you are interested in.

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,

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.

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.

sir , hi i wanated to know each detailing formulas conserned with torque & what is it