Aeroacoustic experiment and broadband noise model of contra-rotating ducted fan under different rotating speeds

Compared to a single rotor fan, a contra-rotating ducted fan (CRDF) has more power output per unit volume and can effectively reduce the weight of propulsor. However, contra-rotating turbomachinery has a stronger aerodynamic interaction between fan rows, consequently a reasonable balance between the thrust advantage and the noise disadvantage is required. In this paper, aerodynamic and aeroacoustic experimental studies were performed on a small-scale electrical contra-rotating ducted fan which is applicable to the propulsor of electrical unmanned aerial vehicles (UAV). The influence of different speed matching of the two rotors on noise characteristics is studied. The dominant tone of contra-rotating fan is concentrated at the harmonics of the front rotor BPF. Increasing the front rotor rotating speed leads to increasing noise. However, speeding up the rear rotor appropriately can reduce the noise. Regarding the present electrical ducted fan, a corrected broadband Heidmann noise model is established by analyzing the original thermodynamic parameters of the compressor with the motor power to obtain the characteristic sound pressure level. The prediction of the spectrum content of the original rotor-stator fan is extend to the contra-rotating fan. The proposed noise model can predict the broadband noise of the CRDF efficiently and accurately in the frequency range of [100 Hz, 10,000 Hz], which has been validated through the present experiment data. These works are important for the future synergistic design of aerodynamics and aeroacoustics of CRDF propulsors.