In cooperation with the University of Siegen, Senvion is researching the onshore rotor blade of the future: it is intended to be quieter – and to grab even more energy from the wind. In an interview, Dr. Sascha Erbslöh, Team Leader for Aerodynamics, talks about serrations, simulations, and limits on “the big one”.
Dr. Erbslöh, is the RENEW project mainly aimed at developing more economical blades, or quieter blades?
The two go hand in hand. Our customers often build close to residential areas, therefore, the equipment has to run quietly. Even so, it has to run as much as possible at maximum load, at night also, because the operators lose output in the noise-reduction mode. Thus, if we build quieter systems, they do not need to be run in the low-noise mode so often. This makes them more cost effective.
What is your approach to the problem?
Most of the rotor noise comes from the dispersal of air at the trailing edge of the blade. Therefore, for the next generation of our onshore systems, the Eco Blade Control (EBC) platform, we are planning to use serrations – a simple geometric change that makes a big difference. But, we are already asking ourselves how we can improve our systems yet further.
Do you have any ideas?
We want to actively influence the airflow, directing the shear layers and turbulence on the profile before even reaching the trailing edge.
But surely you could just have the systems running slower.
That would be counterproductive, because the driving torque increases at lower rotational speeds – and the output drops. Our goal is to reduce the sound power level at proportionate blade tip speeds.
You are now researching into the rotor blades of the future together with the University of Siegen. What can the scientists there do that Senvion cannot?
The Institute of Fluid Dynamics and Thermodynamics has a huge data centre. The enormous computing power allows a level of detail and depth of simulation that we would not be able to even approach at our capacity. Besides, we have had a close scientific collaboration for several years.
To what extent can new aerodynamic profiles be reliably developed on a computer?
Criticism of purely academic studies is justified. We will be testing our solutions under representative operating conditions. We can run smaller aerodynamic tests in the wind tunnel at the university, but we will also be going into really big tunnels.
Rotor blades are getting longer and longer. In theory, yield increases with size, but where is the limit of what is possible?
The rotor blades of our new EBC platform are 68.5 meters long. Even at that length there are logistical limitations, because they are transported over land. The blades could also be produced in sections, but modular assemblies are more vulnerable.
When is the RENEW project due to be completed?
In three years. The Ph.D. students at the University of Siegen are already beavering away. Our customers can already look forward to even quieter rotor blades that further optimize potential yields.
(Interview: Udo Taubitz)