An investigation of the noise characteristics of a small-scale rotor in axial descent

In this work, the acoustic characteristics of a small-scale drone rotor in axial descent are numerically investigated. Various descent speeds covering different working states are tested, and the corresponding effects on the noise are analysed. The turbulent flow fields are obtained using delayed detached eddy simulations and an acoustic-wave preserved artificial compressibility method. The far-field noise is obtained by an integral solution of the Ffowcs-Williams and Hawkings equation. The aerodynamic force and the noise features are also evaluated experimentally in anechoic wind tunnel tests, and test data are used to validate the numerical simulations. The results show that the increase in descent speed leads to a reduction in the mean thrust. Significant thrust fluctuations are also observed when the rotor approaches the vortex ring state. Consequently, a substantial increase in sound pressure level in the low to medium frequency range is found in the far-field noise spectra, while the high-frequency sound pressure level shows a slight decrease. Furthermore, a noise source analysis is performed on the blade surface to help understand the corresponding noise mechanism.