On the sensitivity of the acoustics of short circular holes to inlet edge geometries

Abstract

Short circular holes with a low Mach number mean bias flow passing through them can absorb or generate acoustics. A recent semi-analytical model (Yang & Morgans, Journal of Sound and Vibration, 384 (2016) pp. 294-311 & 393 (2017) pp. 41-61) based on the Green’s function method has been shown to be able to capture both the acoustic absorption and generation. The model indicates the importance of accurately capturing the path of the shed vorticity from the hole inlet edge. In the present work, the effect of this vorticity path on the hole acoustics is first studied systematically using the semi-analytical model. As the vorticity path is sensitive to the sharpness of the hole inlet edge, CFD tools are then used to obtain the vortex sheet shape after slightly changing the hole inlet edge shape. The acoustic responses of these modified holes are obtained using the semi-analytical model. A slightly chamfered edge case and a small ellipse edge case are considered to show that a very small change to the shape of the hole inlet edge can give a significant difference in the hole acoustic response.