On the Generations of Whistle Noise from an Airfoil and a Simplified Side Mirror

*† ‡ § A specified geometry in the laminar flow generates a tone noise for some conditions. The tone noise from an airfoil has been received much attentions since 1970s. Experiment for the NACA0012 airfoil has been conducted using LDA(Laser Doppler Anemometry) and numerical analysis about the airfoil has been carried out to identify the mechanism of whistle noise. Linear flow instability theory based on the assumption of quasi-parallel and small disturbances shows good agreements with the experimental data for the dominant tone frequency. Whistle noise was also observed from a side-mirror of auto vehicle, which is a blunt body. A simplified side mirror model is used in the KAIST anechoic wind tunnel to find the mechanism but the conventional model does not generate the tone noise. So, we designed another simplified auto-vehicle side-mirror geometry generating the tone noise. The new model is designed based on the mechanism of the airfoil geometry. Using this simplified new side-mirror geometry, we conducted experiments for various angle of the geometry at selected flow speed. A high frequency tonal noise and its harmonics are clearly observed and another narrow band frequency with its harmonics is also found at the same time. The two different mechanisms of tone noise exist also in an airfoil of NACA0015 but the phenomena are clearly shown in this thick blunt model.