Theoretical and experimental study on noise reduction characteristics of perforated liners

<p indent="0mm">Perforated liners have a wider noise reduction frequency band than Helmholtz resonators and are often used to suppress combustion instability in aeroengine combustion chambers. With the further improvement in energy density of combustion chambers, the combustion instability presents a multifrequency, composite instability mode. A multicavity, segmented acoustic liner design can be used to develop an effective suppression method for combustion instability in a wide frequency range. However, the current research on perforated liners mainly focuses on plane wave incidence and barely considers the circumferential mode. The transfer element method converges well and can quickly provide accurate theoretical predictions. Herein, this method is used to predict the transmission loss of axial single-segment and segmented perforated liners in the circumferential mode. It is verified on a high-order modal acoustic waveguide test bench. It is found that the frequency band with a transmission loss of <sc>&gt;10 dB</sc> is <sc>~200 Hz</sc> when the plane wave is incident on the perforated liner wide. Furthermore, a parametric analysis based on the perforation rate, back cavity length, and back cavity depth of the single-segment acoustic liner is performed. The influence of the three parameters on the transmission loss curve is summarized, and sound pressure distribution inside the back cavity is used to explain the acoustic resonance mechanism.