- #1
danielhugo
- 6
- 0
Hello, I am Daniel from La Plata, Argentina and would like some help on a complex (for me) question. I am working with some friends on the development of an innovative wind turbine. We have built several prototypes with diameters of 0.5 m and 2 m. We have tested these prototypes on trucks with the assistance of people from the Fluid Dynamics Lab from the Department of Aeronautical Engineering, La Plata National University. In order to measure torque, a 0.3 m wheel was braked by means of a metal strip wound around said wheel and at the end of which different weights were hung. By means of a tachometer the rotor speeds were measured and after many readings we got a clear picture of what kinds of power our turbine was producing. The report from the lab gave a Cp of 0.53 which is very high for a two-meter rotor. However, we were not pleased with some aspects of the procedure and we firmly believe this Cp should have been a bit higher. Now, if the lab had the right device for measuring torque (i.e.:torque transducer) I would not be asking for help. The fact is, we don't have it nor can we buy one, as they are very expensive (something like U$6000). In the meantime I have been trying an alternative way to do this which seems to give good results but that is systematically rejected by the people who specialize in wind turbines.
Description of method: The rotor's mass is constant so when it accelerates in a given wind, it does so with an acceleration = torque/mass. This acceleration will depend essentially on wind speed. If tests are carried out in the open with non-turbulent winds it is possible to make accurate measurements by means of a digital camera. Basically we are interested to know how long it takes for the rotor to go from rest to final speed (to measure angular speed we take a video and then process it frame by frame - it lasts about 40 seconds when wind speed is about 5 m/s). Now knowing the moment of inertia of the rotor it is a simple step to calculate the energy stored in it. If you have the number of joules stored and the number of seconds necessary to do the job, it is easy to calculate the average power produced by the rotor. By means of some maths, it is possible to calculate peak power based on average power (This conversion needs a factor which is dependent on the beta angle which is the angle between chord and rotation plane). I like this method mainly because it is non-invasive, it can be done as many times as one feels necessary and because it costs nothing. My question is then: Do you see anything in this procedure that is not acceptable from a physical point of view? Is there anything else we might do to improve our methodology? Thanks in advance,
Daniel
Description of method: The rotor's mass is constant so when it accelerates in a given wind, it does so with an acceleration = torque/mass. This acceleration will depend essentially on wind speed. If tests are carried out in the open with non-turbulent winds it is possible to make accurate measurements by means of a digital camera. Basically we are interested to know how long it takes for the rotor to go from rest to final speed (to measure angular speed we take a video and then process it frame by frame - it lasts about 40 seconds when wind speed is about 5 m/s). Now knowing the moment of inertia of the rotor it is a simple step to calculate the energy stored in it. If you have the number of joules stored and the number of seconds necessary to do the job, it is easy to calculate the average power produced by the rotor. By means of some maths, it is possible to calculate peak power based on average power (This conversion needs a factor which is dependent on the beta angle which is the angle between chord and rotation plane). I like this method mainly because it is non-invasive, it can be done as many times as one feels necessary and because it costs nothing. My question is then: Do you see anything in this procedure that is not acceptable from a physical point of view? Is there anything else we might do to improve our methodology? Thanks in advance,
Daniel