Adaptation of the Dean method to determine the acoustic characteristics of liner samples based on numerical simulation of physical processes in a normal incidence impedance tube

The work considers adaptation of the in situ method (proposed by Dean) to determine the acoustic characteristics of liner samples based on numerical simulation of physical processes in a normal incidence impedance tube. The numerical simulation is based on a direct solution of the unsteady Navier-Stokes equations in a three-dimensional formulation at high sound pressure levels (130, 140 and 150 dB). To verify the numerical simulation the natural experiments were carried out in a normal incidence impedance tube using the two-microphone transfer function method. It was established that the acoustic impedance and sound absorption coefficient of the liner sample obtained by the transfer function method based on the results of the numerical simulation are in good agreement with the results of the natural experiments. This suggests that used numerical simulation technique qualitatively simulates the physical processes in the liner sample and impedance tube, and the acoustic field parameters obtained at different points of the computational domain are reliable. Processing the pressure - time dependences at points on the face sheet and the back wall of the liner sample in accordance with the Dean method made it possible to obtain the acoustic characteristics of the sample. It is noted that the obtained characteristics are qualitatively similar to the results of previous experimental studies of other authors. The analysis of the results of numerical simulation also showed that as the coordinates of the points change the acoustic characteristics of the sample obtained by the Dean method remain almost unchanged, while the transfer function method is more sensitive to this factor. Thus, the Dean method has a good realizability for determination of acoustic characteristics of liner samples based on numerical simulation of physical processes in a normal incidence impedance tube and in the sequel, it can be conveniently expanded on a case of the grazing waves with flow.