Active Control of Feedback Noise from a Small Step on the surface of Rear-view Mirror

摘要

In order to reduce the aerodynamic tonal noise from rearview mirrors, aerodynamic sound and flow fields around the two dimensional backward-facing step were measured in the wind tunnel. Moreover, active flow control techniques were tested and noise reduction levels were estimated with the fundamental experiments. Since the aerodynamic tonal noise of rearview mirror was generated by a small perturbation caused by a small step on a surface of backward-facing step or rearview mirrors, oscillating jets were introduced to break it. The experimental results showed that the noise reduction level depended on the frequency and intensity of the oscillating jets. The noise reduction level was over 20 dB at the oscillation frequency about 400Hz and the amplitude of the jet velocity about 0.1 m/s. Both of the frequency and intensity of the jet were smaller than the frequency of the feedback noise (2 kHz) and the velocity of the uniform flow (30 m/s). These results indicated that the oscillating jets effectively reduced aerodynamic noise with small amount of energy.