Periodicity of flow and tonal noise characteristics of NACA0018 airfoil

초록

The tonal noise source and the corresponding variation of velocity field are measured to understand the tonal noise mechanism of NACA0018 airfoil. The noise source is evaluated by using the cross-correlation analysis of the sound pressures from two microphones, while the corresponding velocity field is measured by phase-averaged PIV measurement with respect to the tonal noise signal. It is found that the tonal noise is distributed on the pressure surface near the trailing edge of the aerofoil. The phase-averaged PIV measurement indicates that the velocity field near the trailing edge is highly correlated with the tonal noise signaland the separating shear layer on the pressure surface shed the counter-clockwise vorticity near the trailing edge periodically. These results support that the tonal noise mechanism is due the shear layer instability and the following amplification and breakdown of the separating shear layer on the pressure surface