# Torque to power calculation

1. Feb 20, 2009

### yamvmax

I made a wind generating device that produces 120 lbft static torque with a 30mph wind. The paddles that interface the wind have rotational center of 4.5ft(radius). My device will be rotating at 15rpm. How do I calculate how much power is produced at any given wind speed?

Kirk

2. Feb 20, 2009

### minger

$$P = T\omega$$
Make sure your units are correct. You will need to convert rpm

3. Feb 20, 2009

### Dr.D

If you know (from where I don't know) that the device produces 120 ft-lb torque at 15 rpm, you can complete the power calculation that minger has shown by just making the necessary units conversion and doing the arithmetic.

The big question seems to be, how do you know the speed and torque a priori without reference to the wind speed?

4. Feb 21, 2009

### yamvmax

Thank you for the reply minger & Dr.D

The 120 lbft force is what I observed without my device moving (no angular velocity). 15 rpm is the ideal rotational speed due to the mechanical nature of my prototype.

My intuition tells me to calculate the difference between wind speed and paddle speed (2216 ft/min) but I am not sure what to do after that.

I am a ME dropout from 25yrs ago. Maybe I need some refresher courses before I use this forum again?

5. Feb 21, 2009

### Dr.D

Without knowing the geometry of your machine, it is difficult to advise you on how to make a power calculation. You might want to refer to Mark's Mechanical Engineers Handbook for the information in there on windmills for example to see how they are analyzed. That may help you with the analysis of your machine.

The alternative, of course, is to simply try to measure the torque and speed while the machine is rotating. If you can do that, the power output is easy to calculate using the formula that minger has given above.

6. Feb 25, 2009

You would need to know a fair bit more, but taking standard assumptions at 15 m/s with a dia of 4.5 you are looking:

Mass flow = 26.7 kg/s
Theo Power = 5.5 kW
Output from Gen = 2.8 kW

I have made loads of assumptions such as a gen efficiency of 0.5 and coeff of performance of 0.1 and Ro = 1.226.

Some notes http://users.aber.ac.uk/iri/WIND/TECH/WPcourse/ [Broken]

Last edited by a moderator: May 4, 2017
7. Mar 3, 2009

### sonusingh1988

hi Yamvmax i am also making a wind turbine