City Research Online

Abstract

Short circular holes with turbulent bias flows passing through them can absorb or generate acoustic energy. This property is relevant for many industrial applications, such as liners and injectors. A recent study suggested that the acoustic response of such perforations could be strongly sensitive to small modifications of the geometries of their lips. In this work, we study this sensitivity and exploit it to design holes with optimal acoustic properties. To this end, we use a numerical approach based on a two-step method, where a steady mean flow is first calculated as the solution of the incompressible RANS equations. Small-amplitude acoustic perturbations are then superimposed on this mean flow, and their dynamics are obtained by solving the linearised Navier–Stokes equations. To validate the approach, the results are compared with experiments for a hole with sharp edges, finding an excellent agreement. Subsequently, we simulate four holes with modified corners consisting in chamfers or circular fillets either of the upstream or downstream corners. The acoustic absorption is found to be strongly sensitive to all modifications with the upstream chamfer presenting the strongest variations. Finally, we combine the simulations with a Bayesian optimisation algorithm to obtain the size of the upstream chamfer that maximises the acoustic absorption. The optimised hole goes from exhibiting strong whistling to one which strongly damps acoustic energy.

Publication Type:	Article
Additional Information:	© 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Publisher Keywords:	Perforations, Acoustic damping, Optimisation, Bias flow
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology School of Science & Technology > Department of Engineering
SWORD Depositor:	Symplectic Administrator

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