Low-Noise Propeller Design for Future Electric Aircraft

Abstract

Right now electric aircraft are being developed as an alternative to make the aviation industry more sustainable. The electric airplanes available today are using propellers connected to an electric engine as the main propulsion system, and thus the propeller is a critical part of the airplane. This numerical study aims to give a better understanding on how to create propellers optimized for electric aircraft with minimum energy loss and noise emissions. An existing propeller design methodology, implemented in the MATLAB environment as OptoProp, is applied to design a propeller with optimum efficiency. A documented case is then used to verify the applied program. Afterwards, the program is utilised to conduct a parameter study where one or multiple parameters at a given thrust are alternated, and also studying the usage of multiple propellers. Then, the calculated data is used as input for the noise simulations. The results from the parameter study indicates that increasing an individual parameter leads to an improved aerodynamic performance. When testing multiple parameters the positive results from increasing each parameter value continues to a certain point after which the propeller performance decreases. When studying multiple propellers it was found that optimal efficiency is achieved with a four propeller setup. During this project tools used to simulate propeller noise have been developed in a MATLAB environment. The programs are verified by comparing the results to previously documented cases and then used to study sound emissions of single propellers with varying parameters. The results from this study show the impact each parameter has on the noise levels and their correlation with the tip Mach number should be considered. Lastly, sound emissions of multiple propellers and different propeller distributions are studied. This study indicates that the impact on noise far away from the propellers is almost insignificant whereas the noise close to the propellers generally decreases with an increasing number of propellers. Since the conclusions from the two studies differ, compromises had to be made in order to propose guidelines, taking the results from both studies into account. The guidelines contain recommendations for an optimal propeller design, balancing the choice between high efficiency and reduced noise pollution.