Yet another VAWT..... The "Lenz Turbine"
I've always had sort of a soft spot for the Vertical Axis Wind Turbines because of the advantages they offer. Unfortunately, most of them such as the Savonius aren't very efficient but do offer low wind characteristics. About a year ago I was emailed a patent of a VAWT that was a bit different. This one used the "Venturi effect" to duct air around the wings. After reading through the patent I decided to build one and see if It was any better or worse than some of the others out there. As it worked out it did outperform the Savonius but still seemed a bit low on the overall efficiency. I started searching for any others that used this principal and found one other like it. I ended up building this one also and found similar characteristics but this one also seemed a bit low on the efficiency return, still it did outperform the Savinous again.
I started playing around with small units and built a coffee can model which ended up running at 700 rpm and was named the "700 RPM Coffee can". It really didn't make much power being as small as it was and was basically cut and duct taped together. Below shows a picture of the original coffee can experiment... If you decide to try this be advised the metal is very sharp and you should wear gloves as well as observing all safety precautions...
Basically I divided it up into 4 sections, cut two out and taped them back into the can on the two remaining sections. It ran at 700 rpm in a 12.5 mph wind.
I decided to build a larger one using a plastic 5 gal bucket and similar techniques were used in the construction. This was a real dud! It didn't work at all. After some thought as to why it wouldn't work I decided to try a round drum in the center. I stacked a couple large coffee cans inside and taped them in. By changing the airflow through the unit it worked although not very well.
After trying a bunch of different drums and shapes I decided to get a bit more scientific in my testing instead of my hit 'n miss style up to this point. I was intrigued as to exactly what was going on. I started doing some static tests of the air flow through the machine while in different positions but not spinning. Using a hand held wind speed meter I checked the wind speed in front and behind the unit as well as inside. The air flowing through the can was actually faster than the air entering the can. I found some Venturi formula's and started testing shapes and wings. I figured I had enough information to design something a bit larger, and get some better test results. Using a combination of Savinous design ideas along with the venturi theory I came up with a design that is a bit different than the normal. Although similar to the Darrieus, wings similar to the Savonius, and a triangular drum in the middle to guide the flow of air the design was set. I built a few smaller versions for testing and the results looked promising and showed that I seemed on the right track. A larger one needed to be built. Below is the last one built to this point... Simple construction using plywood and aluminum flashing the machine is a bit under built but all the components are in place for the testing...
The alternator is a homebuilt single phase axial design and the first test run showed 17 watts in a 12.5 mph wind. The alternator serves as a pony brake, the stator has bearings and is allowed to rotate, has an arm attached with a spring scale for taking torque readings. From there the output is calculated. The unit stands 2ft tall and 2ft in diameter. I would say it would come close to competing with the Horizontals. It will start turning in a 3mph wind although the alternator doesn't start charging until about 5-6 mph. The turbine ran 240 rpm while driving the 17 watt load which comes out to a TSR of about 1.3. Static testing with my wind meter and unit not turning, 12.5 mph in front of the machine about 3mph 1 ft behind the machine but 17 mph going through the wing. I think there is still a considerable amount of work in improvements to be done and testing will continue. I'm calling it the "Lenz Turbine" and giving credit to all those before me for their unique and innovative work in this field. Also, to Hugh Piggott for helping me with the formula's for working out the wing angles based on the Darrieus type.
Below is a diagram representing the dimensions for the machine above based on percentages of the overall size for those who would like to build one for their own personal use and/or for testing purposes.
Lenz v2 ... update 8/28/05
Another update to the fascinating worl
Below shows the beginning of the second version. Using parts from the first one and some quickie fabrication for the wings I began testing the unit. The alternator is a 12 pole 3phase machine I made up just for this project.
It took some tinkering to get it where I thought it should be with good and not so good results.
Since the unit was slightly different than the original my wing angles didn't work out real well. I played with one wing on the machine to find out where the torque was as it progressed around the 360 measuring every 10 degrees. I realized at that point the torque wasn't where I had thought and started playing with wing angles again. Finally it was dialed in at 9 degrees and worked like a dream!
It was time to take it outside for some real world testing. I mounted it on the front loader of my tractor and out in the wind it went.
The wind was dying down by the time I got it in position so I really didn't get a chance to give it a work out. Below are some output readings...
5.5 mph starts charging
7.1 mph 3.32 watts
8.5 mph 5.12 watts
9 mph 5.63 watts
9.5 mph 6.78 watts
Not to bad for a small 2ft by 2ft machine.
It was time to build a larger one to see if it could be scaled up and still maintain its efficient run.
I built up a larger one 3ft dia x 4 ft tall unit shown below..
I'm not going to get into a lot of details but it does 52 watts in a 12.5 mph wind. I'm not one to be impressed easily, this machine has definitely impressed me. Now, Its time to take it to another level....
Page on building the wings can be found here... Lenz2 wings
www.WindGenKits.com is making a very nice Lenz2 Kit available with all the goodies available for building it from start to finish. They have also produced some very nice videos for building the stator and finishing it up. Everything you need for getting it up and running in short order... check them out !