For more than a decade now, I have been fortunate to get a chance every couple of months to meet with VP for Advanced Technology Programs Michael Idelchik one-on-one to brainstorm new ideas. Early in 2011 during one of our meetings, Michael posed this question to me: Since we know that the inner parts of wind turbines don’t do much for energy capture, why don’t we change the design? This focused our minds to a path to answer GE SVP and Chief Technology Officer Mark Little’s challenge “to build a rotor that could harvest more wind.”
That day when I got back to my office, I called my team – Grover Bennett, Matt Boespflug and Dmitry Opaits – for a meeting. We spent a couple of hours discussing different ideas and came up with the idea of putting a hemisphere on the center part of the wind turbine to redirect the incoming wind towards the outer parts of the blades. The biggest unknown for us was what size the dome should be. As a team, we are used to conducting small-scale bench-top experiments to investigate very quickly whether an idea works. We followed our usual procedure of designing an experiment that could be put together in a couple of hours and running it quickly to get some answers. We bought a 10” wind turbine and several different sizes of Styrofoam balls from the internet. The experiment was set up in our aerodynamic lab in one of our wind tunnels. By cutting the Styrofoam balls in half, we created our domes of different sizes and then stuck these domes on the center of the small wind turbine and ran our experiments at different tunnel air speeds. The picture of the setup is shown below in figure 1.
The wind turbine output was the electricity it produced. We measured the output voltage. Invariably we got a jump in voltage output with the dome placed at the center of the wind turbine; albeit the increases differed for different size domes. A typical set of the data from these runs is shown below in figure 2, where placing the dome at the center of the wind turbine, increases the average voltage output of the wind turbine.
At this stage, our colleague Sachin Premasuthan helped us by conducting several (simplified) computer simulations and showed that the benefits of the dome persisted for the full-scale size wind turbine. Of course overjoyed by the very limited experimental and computational results, we wanted to come up with a name for this design such that it really represented the idea – and was also something that everybody would remember easily. The team gathered in my office again, and after an hour of playing with words the name Energy Capture Optimization by Revolutionary Onboard Turbine Reshape (ECO ROTR) was created.
With these background data in hand; the time had come to present the idea and our plan for further investigations to Johanna Wellington & Keith Longtin, who were at that time the SEAT & Wind Platform leaders respectively. We received overwhelmingly positive feedback and they supported the idea of further experimentation in a controlled environment with larger scale wind turbine. We chose the Gust wind tunnel at the University of Stuttgart in Germany, a picture of which is shown figure 3. The diameter of the circular working section of this wind tunnel is 6.3 meters. This is a good size for significantly avoiding the wall effects on the performance of a 2 meter rotor wind turbine.
We spent the rest of the 2011 and first half of 2012 designing and building a 1/50th scale model of a GE wind turbine. This included designing the entire drivetrain for the turbine at that scale. This task was performed by Christoph Boeld from GRC Munich. Most of the components of the turbine were manufactured in Germany, all of which were coordinated by Robbert Pannekeet. The 2 meter ECO ROTR wind turbine as installed in the Gust wind tunnel is shown in figure 4 along with the experimental team.
We conducted a significant number of experiments at the Gust wind tunnel for different tunnel air velocities and wind turbine tip-speed ratios with several variations of domes. Wind tunnel was also operated at its maximum speed for the blades in feathered configurations at several yaw angles of the turbine to simulate gust conditions. The attached movie shows one of these runs, where the rotor speeds up to 1000RPM.
In all the above cases we measured the efficiency of the wind turbine with and without the dome. Again the results from these experiments were very encouraging and supported the earlier bench-top cases that the dome improved the performance of the wind turbine.
By the fall of 2012 we had completed our first set of tests at the Gust wind tunnel. Our new wind platform leader Mark Jonkhof and Johanna Wellington joined us and we presented the results to Vic Abate (Vice President, Power Generation Products) and his team. Vic was very supportive and encouraged us to plan and conduct these experiments at full scale. With support from Mark Little, Michael Idelchik, Gary Leonard (then Technology Director, Aero-Thermal and Mechanical Systems) and more recently James Maughan (current Technology Director, ATMS) and Mike Bowman (Sustainable Energy Advanced Technology Program Leader), that has come to fruition. That story will be told by my colleagues in an upcoming blog post.
However, since our 2012 experiments, we have also successfully tested a number of different ideas as the next steps for ECO ROTR in the Gust wind tunnel, which will be presented in the near future.
Oh, I forgot to mention that we also conducted surface-dye flow visualization experiments – the conclusions from those results are little uncertain, however, I think the effect of conducting the experiments in tunnel had on me is very clear.
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