Evaluation of Three Impedance Eduction Methods for Acoustic Liners Under Grazing Flow
Regular paper
Federal University of Santa Catarina
Wednesday 3 june, 2015, 16:20 - 16:40
0.3 Copenhagen (49)
Abstract:
The growth of the aircraft transportation sector coupled with the urbanization
of airport surrounding areas brought with them stricter regulations regarding
aircraft noise, mainly during take-off and landing, where engine noise
dominates. This paper focuses on the comparison of three different indirect
methods to measure the impedance of acoustic liners used in the treatment of
aircraft engines. Data obtained from Finite Element simulations of a test
setup considering different flow velocities were fed as input to the three
methods, which attempted le to find the correct impedance imposed in the
numerical model for each flow speed. An analysis was made in order to evaluate
the capacity of the methods to handle higher order modes in the test duct and
the effect of the position of the flush-mounted microphones on the duct side-
walls. It was found that, even though the methods assume plane-wave
propagation in the hard-wall portions of the duct, they are able to converge
to correct results if the microphones are positioned in nodal positions of the
higher order modes cut-on on the frequency range under analysis. The
robustness of each method to errors in the input data was also evaluated.