Initial Comparison of Noise Emissions of Distributed Electric Propulsion Systems for a Regional Aircraft

The use of electric propulsion systems is an important approach to reduce the environmental impact of aviation. Many of these aircraft concepts are powered by a set of propellers that are driven by electric motors. The present paper describes a study on the noise generated by distributed electric propulsion systems. By varying the number of propulsion units (while keeping the total thrust constant) different propulsion systems are obtained. The study investigates their noise emission. As the main focus of the current work is on the contribution of noise from the electric machines, the noise generated by the propellers is calculated in a simplified manner using a well-established analytical model. For the noise emissions of the electric machines, finite element analysis is employed. The noise radiation of the considered motors, due to the electromagnetic forces acting inside the air gap, shows a strong dependency on the operating conditions. Especially, the rotational speed is important as it governs the excitation frequencies which interact with eigenfrequencies of the stator and lead to high sound radiation of the structure. The resulting overall sound power levels for each of the different propulsion system are dominated by the noise contribution from the propellers. Although, the noise emissions from the electric machines show level differences up to 10 dB for the different configurations, the overall sound power level of the total number of propulsion units remains constant at 120 dB.