Article
Reduction of rotor aerodynamic noise using porous blade tips (de)
* Presenting author
Abstract:
Motivated by promising results from experiments on the noise reduction performance of finite wall-mounted airfoils with a porous tip in an aeroacoustic wind tunnel, corresponding measurements were performed in a dedicated rotor test rig. This rig features a 3 kW direct-drive electric motor with three rotor blades of 1.1 m diameter. In the experiments, a variety of different tip modifications was tested regarding their noise reducing performance, including different porous materials that were manufactured using rapid prototyping. Acoustic measurements were performed at different rotationals speeds and blade angles using a ring-shaped microphone array consisting of 60 evenly spaced microphones. The rotational speed was measured using a laser sensor. Different beamforming algorithms were used in post-processing to help analyzing the data. The results show that porous tips can lead to a notable noise reduction at low frequencies, but a small penalty at medium and high frequencies which may be due to the surface roughness of the porous tips. This trend seems more severe for lower blade angles than for higher ones. These findings agree well with those obtained from the previous wind tunnel measurements.