The sound generated or absorbed by short circular holes with a mean flow passing through them is relevant in many
practical applications. Analytical models for their acoustic response often ignore the fact that such holes open to
a confined or finite space either side, or account for this e
ect simply by adding an end mass inertial correction.
The vortex-sound interaction within a short hole has been recently shown to strongly a
ect the acoustic response at
low frequencies [D.Yang and A.S.Morgans, J Sound Vib 384 (2016), pp.294 – 311]. The present study considers a
semi-analytical model based on the Green’s function method to investigate how the expansion ratios either side of a
short hole a
ect the vortex-sound interaction within it. After accounting for expansions to confined spaces using a
cylinder Green’s function method, the model is substantially simplified by applying a half-space Green’s function for
expansions to large spaces. The e
ect of both the up- and downstream expansion ratio on the acoustics of the hole
is investigated. These hole models are then incorporated into a Helmholtz resonator model, allowing a systematic
investigation into the e
ect of neck-to-cavity expansion ratio and neck length. Both of these are found to a
ect the
resonator damping.