AEROACOUSTIC INVESTIGATION OF PROPELLERS WITH UNEVEN BLADE SPACING

Abstract

Propeller noise can be a significant health hazard affecting both mental and physical well-being. In recent years, the rapid growth of the Unmanned Aerial Vehicle (UAV) market has highlighted the importance of reducing noise generated by propellers. This thesis presents the investigation of aeroacoustic and aerodynamic performance of the rotors with uneven blade spacing as a potential noise mitigation technique. APC 27 × 13 rotor was used to construct six rotor configurations with varying blade spacing. 4-bladed evenly spaced configuration served as the baseline rotor. Transient aerodynamic investigation were carried out using Unsteady Reynolds Averaged Navier–Stokes (URANS) equations in an open-source computational fluid dynamics (CFD) solver. The rotation of the blades was achieved by using sliding mesh approach, which implements the physical rotation of the rotor. Pressure fields on the rotor blades obtained in the CFD simulation were interpolated onto a structured grid and subsequently used as an input data for an aeroacoustic model. The acoustic modeling was conducted by integrating the Ffowcs Williams–Hawkings (FW–H) equation using the PSU-WOPWOP software. The results showed that the uneven blade spacing altered the periodicity of the acoustic pressure peaks, effectively redistributing tonal noise energy into lower frequency bands. Increasing the axial distance between the rotors led to a reduction of the loading acoustic pressure, which is attributed wake dissipation between the rotors. To evaluate the advantages of using unsteady simulation, the results were compared to the steady-state Multiple Reference Frame (MRF) simulation. The unsteady simulations showed higher loading acoustic pressure. However, the contribution of loading noise to the total acoustic pressure remained limited. Furthermore, 5-bladed rotor configurations were examined to further assess the influence of index angle on the tonal noise behavior.