Initial acoustic investigation of electric motors for future aircraft engines

Abstract

Due to the increasing requirements in accordance to more sustainable infrastructure and a zero-emission strategy in transportation, new and innovative technologies are needed. The aviation industry, in particular, is responsible for about 4- 5% of the global greenhouse gas emission. Therefore, scientists, aviation companies and policy makers are working on new solutions to reduce greenhouse gas emissions and global warming. One of these innovative solutions might be the use of electrified propulsion systems. Due to their early stage of development, electrified propulsion systems have become one of the main topics in aeronautical research and development for short-, mid- and long-range aircraft. Currently, fully or hybrid electric propulsion systems are especially promising for small aircraft due their light weight and short flight range. Urban Air Mobility and Small Aircraft Transportation is a rapidly evolving industry, enabling the start into more sustainable but also more individual means of transportation in urban areas in the next 10 years. In addition to achieving low greenhouse gas emission the reduction of the noise radiated by the electrical powertrains is necessary for securing the success of electrified aircrafts. A key component of an electrified propulsion system is the electrical machine, for which the high-power and high rotational speed requirements will result in tonal noise emissions that need to be investigated. This study provides details on initial empirical and analytical acoustic investigations for electric machines intended for their use in aircraft propulsion systems. These models include electromagnetic, vibration and noise predictions. Thereby, the aim is to provide an overview of existing noise and vibration emission models of electrical machines which are suitable for aircraft applications. This overview will set the foundation for planned measurements and will enable the verification of numerical noise prediction models. Currently, existing analytical models that predict sound intensity or sound power level of electrical machines are being implemented and verified using test cases of permanent magnet synchronous machines and reluctance machines from the literature. The investigation includes the analysis of the sensitivity of these models with respect to parameters such as motor topologies, power and rotational speed. As a result, a first assessment of the ability to apply electrical machine calculation methods to distributed electric aircraft propulsion systems is made.