Design process for a highly-efficient low-noise propeller

elib (German Aerospace Center)

Abstract

The electrification of air mobility presents challenges for propeller manufacturers while enabling new air transport concepts. This dissertation analyses and optimises electrically driven propellers, focusing on general aviation propellers, lift propellers, and tilt propellers - those that benefit the most from the electrification. A central challenge is balancing noise emissions and energy consumption across varying operating conditions. The thesis begins by evaluating and validating an extended blade element momentum theory(BEMT) for performance prediction by comparing it with wind tunnel tests and CFD RANS simulations. The validation demonstrates that the BEMT predicts thrust and torque with an accuracy of 10%. Subsequently, different aero acoustic modelling approaches are introduced. Farassat’s tonal noise model and the broadband noise model of Brooks, Pope, and Marcolini (BPM) are validated against experimental data, demonstrating reliable noise predictions within an accuracy of ±7 dB. The tonal noise models by Gutin and Hanson are assessed under various flight conditions and compared to the previously validated Farassat model. The assessment reveals that Gutin’s andHanson’s model do not reliably predict the tonal noise emissions. A genetic algorithm is used for multidisciplinary optimisation (MDO), combining BEMT with Farassat’s tonal and BPM broadband noise models. The MDO compares noise emissions and energy consumption over a flight mission to identify the optimal balance between them. The MDO is extended to include models for the motor efficiency, the motor mass, and the propeller mass prediction. In the first step, blade number and diameter are optimised followed by the optimisation of chord and twist distribution. The MDO is applied to a generic flight mission comprising hover, transition, and cruise phases. The influence of each model is assessed individually. The assessment highlights the need fora multidisciplinary, step-wise approach to optimise noise emissions and energy consumption. Comparing fixed- and variable-pitch propellers for the reference mission shows that the variable pitch propeller is only 6.5% more efficient. This dissertation advances the development of electrically driven propellers by introducing a validated optimisation framework and outlines the necessary steps to further improve the optimization process.

Authors 1

1. Ole Bergmann corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen