Reduction of Propeller Noise for Future Electrical Aircrafts

Research Project, 2019 – 2021

Background to the project

As a new way for transportation, electric aircrafts have been attracting extensive attention due to low CO2 emission. However, low noise
emission is crucial for electrical aircrafts to be accepted to transport in urban areas. Electric propulsion systems therefore need to be improved to reach this goal. Since the propellers of the systems are known to dominant the noise generation, we are doing research on reduction of propeller noise at Chalmers, particularly for electric aircrafts.

Boxprop, developed by Prof. Grönstedt’s group at Chalmers ( US patent, "Air propeller arrangement and aircraft") can be one concepts for the next generation of aircraft propellers. Several recent studies by Prof. Grönstedt’s group have shown that this concept has high potentials to improve the propulsion efficiency and noise emission.

Aims

This project aims to explore the potential usage of Boxprop for future short-range electrical aircrafts as a future public urban transportation service. The feasibility of Boxprop will be addressed and demonstrated based on numerical simulations and experiments. The aeroacoustic and aerodynamic performances of a set of propellers, which are designed with different geometrical parameters and rotational speeds, will be investigated. The findings will be used to improve the existing propeller configurations.

Methods

A high-fidelity computational fluid dynamics (CFD) method, detached eddy simulation (DES), will be employed in the flow simulation. This method can well resolve turbulent structures at high Reynolds numbers but consumes much less computational resources than direct numerical simulation (DNS) and large eddy simulation (LES).

The Ffowcs Williams and Hawkings method (FW-H) will be used in the noise prediction. The FW-H method belongs to the family of the acoustic analogy originally proposed by Lighthill (1956). An apparent advantage of the FW-H method is that it separates the aeroacoustic and aerodynamic simulations. Therefore, numerical errors in the aerodynamic simulation will not contaminate the aeroacoustic prediction.

The near- and far-field noise levels of the configurations at various rotational speeds will be measured in an anechoic chamber. The ambient air in the chamber is quiescent to make the free-stream velocity zero. Operations with multiple propellers will be tested to explore the interaction between propellers.

Measurements

The noise measurement will be carried out at the anechoic chamber at the division of Applied Acoustics at Department of Architecture and Civil Engineering in Chalmers.