An Experimental Facility for Measurement of Acoustic Transmission Matrix and Acoustic Power Dissipation of Duct Discontinuity in Higher Order Modes Propagation Conditions

摘要

An original experimental facility for measuring acoustic transmission matrices of duct discontinuities is described. It is an extension of a previous method developed for measuring reflection matrices and based on measurement of acoustic pressure in two closed cross sections which separates incident and reflected modes after a modal decomposition by a Fourier-Lommel's transform. In the new facility, the discontinuity is located between two measurement duct elements, and the entire experiment is automatic and controlled by a working station. The formulations and the flow diagram of the specific data treatment procedure which are performed to determine the reflection and transmission matrices' coefficients, the axial acoustic intensity per mode and total acoustic powers are described in detail. An experiment with a hard wall duct test section without any discontinuity was conducted. Results of reflection and transmission matrices, acoustic powers and intensities are discussed.