Chris Olson
12th July 2011, 13:24
I don't see many folks posting projects or experiments here, so I thought I would share one.
I recently put an experimental four-blade rotor on one of my turbines (see attached photo). The main purpose of the experiment was to see if I could increase the solidity of the rotor in the swept area and slow the rotor down more, using a higher gear ratio in the transmission that drives the generator. The slower rotor speed will help with blade life, reducing leading edge erosion in installations where the turbine experiences high levels of abrasives in the air (bugs, dirt, water, etc).
The experiment was successful and the four-blade rotor actually made very slightly more power @ 12 mph wind speed than the three. But there was a surprising twist.
I have long had struggles with my turbines to keep them under control in very high winds. The type of airfoil used on their rotor (GOE222) does not react well to furling and continues to develop sometimes better than twice the rated peak power of the machine, even running furled, in 60-70 mph winds.
This four blade rotor uses a modified GOE222 airfoil with the trailing edge straightened to remove some of the "cup" from the high pressure side of the airfoil. We had 60 mph winds on Sunday morning and close to 80 mph on Sunday night and the machine with this experimental rotor never exceeded 1800 watts. The three bladers were pushing very close to 4 kW.
At 25 mph, where the machine is rated at peak power, it's down roughly 12% on power as compared to the three blade rotor. I'm finding that I have to turn the pressure up on the power limiter up to get the machine up to rated peak power at 25 mph with this rotor on it. If it is turned out of the wind more than about 35 degrees it basically shuts down and stalls.
I included three photos - the first is the turbine with the four blade rotor, the second is the GOE222 airfoil used on the three blade rotor, the third is the modified GOE222 used on the four blade rotor.
Very interesting and fun experiment. The next thing I'm going to try is building another set of modified GOE222 blades and put them on a three blade machine to see what happens.
--
Chris
I recently put an experimental four-blade rotor on one of my turbines (see attached photo). The main purpose of the experiment was to see if I could increase the solidity of the rotor in the swept area and slow the rotor down more, using a higher gear ratio in the transmission that drives the generator. The slower rotor speed will help with blade life, reducing leading edge erosion in installations where the turbine experiences high levels of abrasives in the air (bugs, dirt, water, etc).
The experiment was successful and the four-blade rotor actually made very slightly more power @ 12 mph wind speed than the three. But there was a surprising twist.
I have long had struggles with my turbines to keep them under control in very high winds. The type of airfoil used on their rotor (GOE222) does not react well to furling and continues to develop sometimes better than twice the rated peak power of the machine, even running furled, in 60-70 mph winds.
This four blade rotor uses a modified GOE222 airfoil with the trailing edge straightened to remove some of the "cup" from the high pressure side of the airfoil. We had 60 mph winds on Sunday morning and close to 80 mph on Sunday night and the machine with this experimental rotor never exceeded 1800 watts. The three bladers were pushing very close to 4 kW.
At 25 mph, where the machine is rated at peak power, it's down roughly 12% on power as compared to the three blade rotor. I'm finding that I have to turn the pressure up on the power limiter up to get the machine up to rated peak power at 25 mph with this rotor on it. If it is turned out of the wind more than about 35 degrees it basically shuts down and stalls.
I included three photos - the first is the turbine with the four blade rotor, the second is the GOE222 airfoil used on the three blade rotor, the third is the modified GOE222 used on the four blade rotor.
Very interesting and fun experiment. The next thing I'm going to try is building another set of modified GOE222 blades and put them on a three blade machine to see what happens.
--
Chris