Since our last post the wind turbine team has been single-mindedly focused on our wind tunnel tests at the NASA-Ames research center. This testing opportunity will be a godsend for us as we will finally be able to get some clean, quality data concerning the performance of the two turbine styles we are evaluating: Savonius and Lenz. Good bye chasing wind around San Francisco!

What we are most excited about is the controllable nature of the wind tunnel and the ability we will have to set our test parameters. As a result of this unprecedented level of control, we will finally be able to apply a degree of rigor to our tests that has previously been unattainable. This more scientific approach will allow us to accurately predict not only the performance characteristics of the turbines, but also determine the appropriate alternator specifications for maximum power extraction from the system.

The tunnel in which we will perform the tests is a 7’x10’ wind tunnel owned by NASA, but leased to, and operated by, the US Army – specifically the Aeroflightdynamics Directorate (AFDD). We are extremely grateful to both the US Army and the folks at the test facility for their generosity and assistance. Without this unique opportunity, we would be hard pressed to continue making substantive progress with our turbine design.

Over the past handful of weeks Jeremy Kimmel, our wind turbine intern, and Malcolm Knapp, an EWB/Catapult volunteer, have been diligently working out the bugs in our set-up. Malcolm has spent countless hours programming the Data Acquisition System (DAQ) and they have both made a number of trips down to the test facility in order to ensure that we’ll be ready once the wind tunnel is ready for our appearance. Speaking of which, we’ve been told that we will finally get into the tunnel on August 17th! There have been a number of delays, but it is finally going to happen.

Below is a photo from our data collection training session just prior to shipping the turbine down to the NASA-Ames facility. We are fortunate enough to have an entire two weeks of dedicated wind tunnel time! During that period, Jeremy, Sarah, and Charlie will be leading our testing efforts and maintaining a constant presence at the tunnel. A number of other volunteers will cycle through to lend a hand and participate in this major testing milestone. Stay tuned for a post about our wind tunnel experience…

Left to right: Sarah Felix, Malcolm Knapp, Charlie Sellers, and Jeremy Kimmel

It’s looking more and more like our proposed NASA testing will indeed happen. In fact, the testing schedule has been accelerated and we’ve been told to be ready to go by the end of April! Thankfully we’ve already been hard at work getting our new Lenz blades built and sprucing up our old Savonius blades for prime time. In the below photo you can see Charlie assembling the “spines” of the Lenz blades over which well will affix some light plastic sheet. These blades reportedly have some very exciting performance characteristics and we’re looking forward to seeing how they perform in the tunnel.

In addition to making certain the turbine is mechanically ready for the wind tunnel we have also been busy jumping through the hoops that NASA and the Army (which manages the the 7′x10′ wind tunnel we’ll be using) sets up for all prospective wind tunnel users. One of those hoops is a “failure analysis” of the turbine and its component parts to ensure that the turbine won’t fail during testing and harm the tunnel or its operators.

At the suggestion of the extremely helpful tunnel technicians we’ve been working with we decided to forgo the analytical approach to failure analysis and instead go with real-world “proof” testing. This involves showing the turbine can withstand substantially larger loads than it is expected to see in the tunnel by calculating the maximum load it is should see in the tunnel, multiplying that of a factor (say four), and then subjecting the turbine to that load outside the tunnel. If it survives it should pose no threat to the tunnel at the loads it will see.

In this photo we are applying a 40 lb load horizontal to the middle of the turbine to simulate approximately four times the 11 lb force the turbine is expected to see if we test it to our proposed maximum speed of 25mph. I think it’s going to be ok.

Resin-cast stator based on 200W design by Hugh Piggott.

This last Sunday we cracked open the mold for our new stator based on a 200W design by Hugh Piggott, and this is what we found.  The eight coils seen inside were cast in resin and fiberglass the week before (the colors are from crayon we used to coat the inside of the mold). While we hope to generate only 10% of what this stator was designed for, we decided that building a small alternator on an existing design would not only prove to be educational from a fabrication standpoint, but would also give us a well-understood baseline from which to proceed.  At some point I hope to slap this baby on the bottom of our turbine just to see what it will do.  After all, a direct drive alternator would be superior to a smaller, chain driven alternator for a whole host of reasons…