The industrial PhD experience

    Carlos Arce León joined LM Wind Power’s Aero Group to complete a PhD project on blade serrations and noise reduction, funded by the Innovation Fund Denmark. Now nearing the end of his PhD, Carlos shares his fascinating research and reflects on the industrial PhD experience.

    For Carlos Arce León, Acoustic Prediction Methods PhD Student, five years at LM Wind Power has flown by. In fact, he didn’t realize he recently passed the five-year mark, until a colleague reminded him.

    Originally from Costa Rica, Carlos made his first cold step to Scandinavia as a master’s student at Sweden’s Uppsala University. In 2011, he moved to Denmark to join LM Wind Power’s Aero Group to research blade serrations and noise reduction. Now nearing the end of his PhD, Carlos shares his fascinating research and reflects on the industrial PhD experience.

    Why LM Wind Power?

    I joined LM Wind Power to develop a PhD project on reducing the noise impact of our blades, using serrations. Back then within our Aerodynamics group we were building up a section for Aeroacoustics — the research that focuses on how a body moving through air generates noise.

    Applying for PhD funding can have its ups and down, but after two years as an engineer at LM Wind Power, I was excited to learn that Delft University of Technology (TU Delft) accepted my proposal, and that we had funding with Innovation Fund Denmark’s Industrial PhD Program. I had always dreamed of studying aerospace engineering at TU Delft; it’s an awesome university in the Netherlands with a really good reputation in this field. Working for two years before beginning my research definitely benefitted the project, as I had a better understanding of our company culture and what we wanted to gain from a three-year PhD project.

    What is your project?
    Basically the main questions come down to: how much noise do blades make, how much can we reduce this noise and what features can we use to do this? Serrations are a feature that can reduce the noise that blades generate as they cut through the air. We know they work, but in fact the world research community is still trying to find answers to questions that would help explain how they work! Within my PhD, we’re trying to uncover how serrations reduce noise, which will lead to a better and more focused design of our product.

    Ultimately, reducing blade noise can reduce the cost of energy. To give just one example of how they could do that, in some locations, such as Germany, local noise regulations define a maximum nighttime noise level that is lower than the allowed daytime noise level. Consequently, some developers have to shut down their wind farm at night — a huge loss for them. If serrations on blades can reduce noise enough to allow wind turbines to run all day and night, then the farms will produce more energy from their turbines and thus the overall cost of energy goes down.

    Putting serrations on a blade has an impact — sometimes on energy output or on maintenance and installation costs — so we need to determine how the benefits outweigh the costs. From an aerodynamic perspective, serrations de-optimize the blade surface, which may impact the blade’s Annual Energy Production (AEP). So, there’s a balance: If a wind farm can run their turbines overnight by adding serrations, they will gain in overall energy production even with a small decrease in output during the day. Also, serrations can allow blades to spin faster while making the same amount of noise, thus increasing AEP. Overall, customers are beginning to see the benefits of installing serrations, and we now have serrations in production and operation.  

    What has been your greatest research challenge?
    Studying aerodynamics is studying the invisible, and this is certainly a challenge. Studying aeroacoustics, and how sound is generated by the unbelievably fast movement of millions of invisible tiny turbulent structures around an airfoil, is perhaps even more so. On top of that, our goal is to reduce the noise from airfoils that are already relatively quiet, sometimes even quieter than the labs that we work in.

    But cooperating with TU Delft has given us a great advantage. With them, we are at the forefront of flow measurement techniques, especially particle image velocimetry (PIV), which helps us to uncover and see those invisible flow structures. We probably have the world’s most complete experimental dataset on flow around serrations. But that’s merely the first step to explain how they reduce noise. Today we believe we’re getting very close to answering that, and we have already been able to answer many of the questions that we had when LM Wind Power started investigating serrations.

    How do you balance business and academics?
    I love to see the contrast: there is such a different environment in the PhD world, versus the way we approach projects in a business. At LM Wind Power, we focus on the customer with the mentality that we need to design and produce a product. We are more grounded toward the kinds of problems our customers face, and more aware of how our work impacts the greater business picture. We also get to be involved with people from other departments, with whom together we try to find out how to turn an idea into a product that will last and will perform as our customers want.

    Academic settings are quite different. Every third month, I work at TU Delft where I often have the chance to perform a variety of hands-on, customized experiments. In a university environment, one can spend a lot more time focusing on the details, the physics. Asking the right questions is a cornerstone, and it’s this art I’ve appreciated being challenged with the most. Doing science means being rigorous, and often taking slow and careful steps is the only way to advance.

    What comes next?
    I’m in the final stretch of my PhD — the phase when I need to sit down and write, including at least one more article for a peer reviewed journal and the PhD thesis.

    In January, I presented our work on serrations at the American Institute of Aeronautics and Astronautics (AIAA) SciTech conference in San Diego, California. Thousands of professionals attended from across the aerospace community, including Lockheed Martin, NASA, Boeing, and pretty much every one of the world’s best technical universities. It was exciting to put LM Wind Power’s name next to these huge players, and I hope to continue this exposure at future conferences.

    I can’t wait to finish the PhD, but at the same time there are many aspects I am going to miss. I’ve built a close team at TU Delft, and I have even had the honor to be part of laying the groundwork for their aeroacoustics research group. I’m definitely not saying goodbye to them; I hope this is but merely the start of a great cooperation story between LM Wind Power and them, and why not also the growth of a cutting-edge research network in Northern Europe and beyond.

    For more information about serrations and TU Delft’s aeroacoustics research, check out these animations created by Carlos:

    Wind Turbine with Serrations 
    Wind Turbine Sound Sample 
    Calibrating a PIV Experiment

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    Serrations experiment

    Photos courtesy of Carlos Arce León

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