Modal Filters For In-Duct Sound Based on the Cremer Impedance and Micro-Perforated Plates
نویسندگان
چکیده
The design of a new filter-type is presented that allows a sufficient reduction of in-duct aero-acoustic noise. The filter is a hybrid design containing a lined duct section based on the so called Cremer impedance and a section with combinations of micro-perforated plates. The Cremer impedance section strongly damps the zero-order or plane wave mode while the MPP section which breaks the circumferential symmetry of the duct and damps the higher order modes. Different designs are investigated numerically, solving the linearized Navier-Stokes equations in the frequency domain and decomposing the sound-field into its modal components. Both, the transmission loss and the total power loss is calculated and compared for different assemblies and plate impedances.
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