Validation of Standing Wave Liner Impedance Measurement Method

Hersh Acoustical Engineering, Inc. proposes to establish the feasibility and practicality of using the Standing Wave Method (SWM) to measure the impedance of perforate-over-honeycomb liners exposed to both grazing and orifice bias flow. By measuring liner generated reflected sound in a duct, the SWM calculates the impedance of one or more rows of resonator liners, providing the liner axial length is small relative to the wavelengths of the incident sound and the sound frequencies are sufficiently low that the effects of acoustic refraction by mean flow velocity gradients are negligible. Work Plan. Tasks are separated into test preparation, test execution, and analysis and reporting. Tests will be conducted in the University of Cincinnati Grazing Flow Test Facility and most preparation work will be focused on modifying the facility to permit the enabling of bias flow in the facility. The facility design will be such to enable measurements of resonator impedance without grazing flow, with grazing flow and with grazing and bias flow. The following tasks are proposed. Task 1, Design of test resonator, Task 2, Quote, manufacture, and installation of test resonators, Task 3, Modification of test setup and data processing codes, Task 4, Impedance measurements with no grazing or bias flow, Task 5, Impedance measurement with grazing flow and no bias flow, Task 6,Impedance measurement with grazing flow and bias flow, Task 7, Measurement of resonator impedance in the UC acoustic wave tube, and Task 8, Final Report.