Electrification is seen as playing an important role in the fossil-free aviation of tomorrow. But electric flight grapples with a trade-off dilemma: The more energy efficient an electric plane is, the noisier it gets. Now, researchers at Chalmers University of Technology, Sweden, have developed a propeller design optimization method that paves the way for quiet, efficient electric flight.
In recent years, electrification has been described as playing an important role in reducing emissions from aviation in the future. Due to the challenges posed by longer ranges, interest is primarily focused on electric propeller aircraft that cover shorter distances. Propellers connected to electric motors are the most efficient propulsion system for regional and domestic flights.
But while planes are electric, propellers cause another type of emissions—noise. The noise from the fan blades will not only annoy air passengers. Future electric aircraft will need to fly at relatively low altitudes, with noise disturbance reaching residential areas and animal life.
Fight the barter dilemma
This is where the research community faces a dilemma. The ambition to develop electric aircraft that are somewhat quiet and energy efficient has been thwarted by the trade-off issue.
“We can see that the more propeller blades there are, the lower the noise emissions. But with fewer blades, the thrust becomes more efficient and an electric plane can fly longer. In that sense, there is a trade-off between energy efficiency and noise. This is something that is a hurdle for planes. electrics that are both quiet and efficient,” explains Hua-Dong Yao, associate professor and researcher in fluid dynamics and marine technology at Chalmers University of Technology.
Optimized design for quiet and efficient fans
But now, Hua-Dong Yao and his research colleagues may be one step closer to a solution. They succeeded in isolating and exploring the noise that occurs at the tip of the propeller blades, or “terminal vortices,” a known but poorly explored source of noise. In isolating this noise, the researchers were able to fully understand its role in relation to other sources of noise generated by the propeller blades. By adjusting a range of propeller parameters, such as pitch angle, chord length and number of blades, the team found a way to optimize the propeller design and even effect the trade-off between efficiency and noise. The method described in the study published in the journal outer spaceAnd They can now be used in the process of designing quieter propellers for future electric aircraft.
“Modern aircraft propellers typically have two to four blades, but we have found that with six blades designed using our optimization framework, you can develop a fan that is efficient and relatively quiet. The propeller achieves noise reduction of up to 5.8dB* with a thrust penalty of 3.5 Only percent, compared to a three-blade fan. This is similar to the noise reduction of a person who goes from speaking in a normal conversational voice to the sound you might notice in a quiet room,” says Hua Dong Yao.
*dB-weighted (dB or dB(A)) is an expression of the relative loudness of sounds as perceived by the human ear. A-weighting gives a greater value for frequencies in the middle range of human hearing and a lower value for frequencies at the edges than a flat sound measurement in decibels. A weighting is the standard for determining hearing damage and noise pollution.