Impedance Eduction with an Extended Search Procedure

process in which impedance of the sample lining, duct termination impedance, and mean flow Mach number are set and the acoustic field is predicted. A search algorithm varying 5 degrees of freedom (real and imaginary parts of the twoimpedancesandMachnumber)isusedtobest fitthepredictedacoustic fieldtothemeasuredacoustic field.With Mach number as a search parameter, substantially improved data fitting is achieved as compared with the use of an a priori assumption of effective Mach number presumed to account for real flow effects. Published NASA Langley Research Center grazing incidence tube data are used in benchmark examples. Data from the Spirit AeroSystems flow duct facility are used to emphasize the quality of results achieved.