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Impedance eduction method based on multiple measurements with different incident modes in cylindrical ducts with
Haoyu Kuai1, Kang Gao1, Weikang Jiang1
1State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China.
None:
The impedance eduction method is applied in rectangular ducts, with the focus being placed on flat-panel acoustic liner samples traditionally. To measure the accurate acoustic impedance of the acoustic liner in a real engine, it is necessary to extend the impedance eduction method to cylindrical ducts. For the impedance eduction method in circular ducts with large transversal dimensions, consideration must be given to the termination impedance of higher-order cut-on modes. So, an extended impedance eduction method incorporating termination impedance is developed for multimodal acoustic propagation in cylindrical ducts. To simultaneously search for more variables, including the higher-order termination impedance, the multiple measurements with different incident modes are included in the proposed impedance eduction procedure. Numerical simulations and experiments are employed to validate the proposed method. The Monte Carlo Method is used to evaluate the uncertainty from the sound pressure propagating nonlinearly to the impedance.
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