A Chalmers University of Technology Conceptional Design Method for Propellers. An implementation of Drela method for minimum induced loss and Garrick and Watkins method for sound pressure level

Abstract

The ongoing development of electric aircraft aims to make the aviation industry more sustainable, with a focus on reducing energy consumption and noise emissions. Propellers, as a key component of electric airplanes, play a critical role in achieving these goals. This study focuses on designing optimized propellers for electric aircraft that maximize efficiency while minimizing energy loss and sound pressure levels (SPL). By employing Drela’s propeller design methodology for aerodynamic optimization and Garrick and Watkins models for noise analysis. The primary tool used in this study is OptoProp, a numerical simulation program developed in Python to optimize propeller efficiency. The methodology involves several key steps. First, the program is verified using a documented case to ensure its accuracy in predicting propeller performance. Following verification, a parameter sensitivity study is conducted to understand how critical design elements, such as blade count, diameter, and angular speed, influence efficiency and noise levels. The final step involves conducting noise simulations using the calculated aerodynamic data to analyze the relationship between propeller parameters and SPL, providing deeper insight into the effects of each parameter. The results of the parameter study reveal several important trends. The propeller’s diameter and blade count are pivotal in determining its overall efficiency. A larger propeller size enhances efficiency by reducing the power required and lowering the generated torque, both of which are critical for achieving sustainable performance. However, increasing the diameter also leads to a positive effect on SPL, as larger propellers tend to produce less noise due to their inverse relationship with the sound pressure level. While this trend offers a valuable approach to designing propellers with better performance and reduced noise levels, there is a threshold for both the diameter and blade count. Beyond this threshold, further increases in these parameters have detrimental effects on performance and can lead to suboptimal propeller designs. This suggests that simply increasing the size or number of blades does not always result in improved performance, and a balanced design is essential. On the other hand, the effect of angular speed on propeller performance is also significant. Increasing the angular speed improves efficiency up to a certain optimal value, after which further increases yield diminishing returns. However, angular speed has a negative impact on SPL, meaning that higher speeds generate more noise. This introduces a critical trade-off between performance and noise, as designers must be cautious not to increase the angular speed beyond the optimal level if low noise levels are a priority. The sensitivity of noise to angular speed makes it an important factor in designing propellers for electric aircraft, where minimizing noise pollution is a key concern. In conclusion, the study provides valuable guidelines for designing electric aircraft propellers that balance high aerodynamic performance with low noise emissions. The findings suggest that an optimal propeller design must consider not only aerodynamic efficiency but also the impact of various parameters on SPL. The balance between propeller size, blade count, and angular speed is crucial for achieving sustainable performance, with thresholds for each parameter that must be respected to avoid diminishing returns in both efficiency and noise reduction. These insights contribute to the development of electric aircraft technology and offer a pathway toward more sustainable aviation solutions, where both environmental impact and noise pollution are minimized without compromising on performance.