Multiphysics Numerical Simulation of Electric Motor Noise for Electrified Aero Engines

Kurzfassung

In order to contribute to the ongoing efforts against climate change, the European Commission has published a document called Flightpath 2050, which sets out objectives and targets for the aviation sector to reduce the environmental impact of aircraft and their associated and necessary infrastructure. These targets are aimed at reducing water vapour and contrails, ozone and soot, NOx and CO2 as well as noise. In this context, alternative propulsion systems for commercial aircraft are being considered. These new propulsion systems will have electric machines either to drive the propulsor directly or to assist the gas turbine in certain flight phases. At present, different types of architectures of electrified aero-engines and propulsion systems are being investigated by industry and research groups around the world, and there are numerous topologies of electrical machines that may be applicable and suitable for these systems. New motor and generator technologies are also emerging at regular intervals. Although noise from electrical machines has been studied for some time in the automotive and power generation sectors, data, methods and models for electric motor noise for future aircraft propulsion systems are scarce. The high power and speed requirements of electrical machines for future aircraft will result in significant sources of tonal noise. Testbed measurements will help to quantify the resulting far-field noise levels and their directivity. This will pave the way for the establishment of analytical and numerical prediction methods. Experimentally verified numerical simulation methods will provide a better understanding of the physical noise generation mechanisms and support the development of noise mitigation techniques. In this paper, a multiphysics numerical simulation of electromagnetic forces coupled with structural modal analysis is performed to assess the vibration and radiated noise of an electric machine suitable for an aircraft propulsion system. This work includes the calculation of the radial electromagnetic force density in the air gap for machines under different load conditions and the data processing necessary to obtain the temporal and spatial distribution of the stress. Based on these results, subsequent simulations will provide the frequencies and vibration modes of the structure, as well as the vibration velocity and displacement of the casing surface, which will ultimately allow the prediction of the resulting far-field noise levels.