Abstract
A microperforated panel (MPP) is generally defined as a perforated plate, in which the impedance of below one millimetre perforations is dominated by viscous losses. Using MPPs in duct and silencer applications, target is to maximize transmission loss (TL) by choosing proper surface impedance parameters. Additive manufacturing (AM) has recently reduced conventional design limitations and enabled fast prototyping of complex shaped structures. MPP-based model scale silencers can be printed within reasonable time, price, and accuracy. In this paper, design and validation of AM silencers with MPPs are studied. First, the theoretical background of MPP acoustics is summarized. Second, feasible parameters for a MPP absorber for a certain tuning frequency are sought numerically using acoustic finite element method (FEM). Third, several test MPPs are prototyped and their acoustic properties are measured. Finally, MPP silencers are simulated using different approaches and the results are compared against experiments.
Highlights
A microperforated panel (MPP) is generally defined as a perforated plate, in which the impedance of a hole is dominated by viscous losses [1, 2]
The impedance was inserted into the model as numeric data for a 1x1 FE Area Junction, located on the MPP surface of the silencer passage
Three different circular hole options (A, B, and C) of MPP, combined with a suitable backing cavities tuned to 3500 Hz, were designed
Summary
A microperforated panel (MPP) is generally defined as a perforated plate, in which the impedance of a hole is dominated by viscous losses [1, 2]. A Cremer silencer typically works best at the plane wave region They have high TL (peak up to 80 dB) at relatively narrow frequency band. In case of a Cremer silencer, the value of optimal impedance depends on frequency, duct dimensions, and the order of the propagating waveguide mode. A Cremer silencer works best in case the acoustic reaction of the MPP surface is local. Surface, the particle velocity in MPP hole is in the normal direction and the sound field is uniform in the cavity To maintain this in practice, lateral dimensions of the backing cavities should be much smaller than half wavelength at the frequency of interest. The main reasons for performance anomalies are (1) leaks between backing cavities, (2) cavities with too large lateral dimensions (extended reaction), and (3) unsuitable MPP impedance. MPP silencers are simulated using different approaches and the results are compared against experiments
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