Experimental investigations of perforated liners with bias flow based on sound-vortex theory

Some experimental investigations of the acoustic properties of perforated liners with bias flow are presented in this paper. At first, the reflection coefficient of a perforated liner with bias flow is calculated while considering its real structure on the experimental equipment.By choosing perforated plates of different geometrical parameters, measurements are carried out and the experimental results agree with theoretical results well. Both theory and measurements show that the absorption coefficient of perforated liners with bias flow can reach 1.0, provided that its geometrical parameters and flow velocity are chosen properly. Secondly, perforated liners without and with bias flow are compared with each other in this paper. On the condition that the apertures in the perforations are comparatively large, the former tends to have a narrower absorptive band while the latter has a high absorption coefficient with much wider absorptive band by choosing flow velocity properly. Considering that blowing and suction will have different influence on surface shear flow of perforated liners, the comparative experimental results between blowing and suction are also included in this paper.