Electrification is seen as having an important role to play in the fossil-free aviation of tomorrow. But the more energy-efficient an electric aircraft is, the noisier its propellers get. Now, researchers at Chalmers University of Technology have developed a propeller design optimization method that paves the way for quiet, efficient electric aviation.
“We can see that the more blades a propeller has, the lower the noise emissions. But with fewer blades, propulsion becomes more efficient and the electric aircraft can fly for longer. In that sense, there is a tradeoff between energy efficiency and noise. This is something of an obstacle for electric aircrafts that are both quiet and efficient,” said Associate Professor Hua-Dong Yao.
Now, the researchers may be one step closer to a solution. They have succeeded in isolating and exploring the noise that occurs at the tip of the propeller blades — “tip vortices” — a known but less-well-explored source of noise. In isolating this noise, the team was able to fully understand its role in relation to other noise sources generated by propeller blades.
By adjusting a range of propeller parameters — e.g., pitch angle, chord length, and number of blades — the team found a way to optimize the propeller design and even out the trade-off effect between efficiency and noise. The method, published in the journal Aerospace, can now be used in the design process of quieter propellers for future electric aircraft.
“Modern aircraft propellers usually have two to four blades, but we’ve found that by using six blades designed using our optimization framework, you can develop a propeller that’s both relatively efficient and quiet. The propeller achieves a noise reduction of up to 5-8 dBA with only a 3.5 per cent thrust penalty, compared to a propeller with three blades. That’s comparable to the noise reduction of someone going from speaking in a normal conversation voice to the sound you would perceive in a quiet room,” said Yao.