Resolvent-guided optimisation of downstream-edge chamfering for flow-induced noise reduction in a confined orifice

This study develops a resolvent-guided optimisation framework for reducing flow-induced noise in a confined finite-thickness orifice through downstream-edge chamfering under a pressure-drop constraint. The target response is the downstream transmitted in-duct pressure below the first higher-order duct-mode cut-on. A steady base flow is combined with eddy-viscosity-enhanced resolvent analysis to construct a wall-pressure-related source proxy, and the selected design is assessed using large-eddy simulation. The baseline circular orifice supports strong amplification and intense wall-pressure loading over the downstream inner-orifice wall and immediate postorifice region, where in-hole recirculation, separated shear-layer development, and downstream recovery are strongly coupled. The optimisation identifies an optimal downstream chamfer with a length equal to 55 % of the orifice thickness and a chamfer angle of 50°. Rather than eliminating separation, this geometry redistributes amplification-supporting structures, Reynolds-stress concentrations and wall-pressure fluctuations away from the sharp downstream corner, weakening the compact dipole-source region. The wall-pressure spectra are reduced over almost the entire frequency range below the first higher-order duct-mode cut-on frequency, with strong attenuation of the dominant narrow-band peaks. The duct-based surface-pressure contribution remains dominant in the low Mach-number confined flow but is suppressed more strongly than the volume Reynolds-stress contribution. The residual volume source support is redistributed farther downstream with the displaced shear layer. The selected chamfer further retains a clear source-reduction benefit over a moderate Reynolds number range near the design condition. These results demonstrate an efficient route for pressure-loss-constrained noise reduction in confined internal flows.