The nonlinear impedance of perforated walls in the case of two-pure-tone excitation
Abstract
The acoustic impedance of a perforated wall, used as the resistive layer in an acoustic liner for turbojet engines, excited by two tones of discrete frequencies is investigated. Pure tones were excited simultaneously at an exciting frequency, at which acoustic impedance was determined, and at a perturbing frequency in a standing wave tube, and the real and imaginary components of acoustic impedance were determined as functions of the intensities of the exciting and perturbing waves. Results indicate that the perturbing frequency causes the acoustic resistance to increase with perturbing sound intensity, with a corresponding decrease in reactance. The experimental results are correlated with the acoustic velocity in the holes of the wall by means of an acoustic impedance model, and it is shown that the nonlinear dependence of material response on wave amplitude can be accounted for in terms of the impedance resulting from single-tone excitation.
- Publication:
-
Revue d'Acoustique
- Pub Date:
- 1979
- Bibcode:
- 1979RvAc...12...42J
- Keywords:
-
- Acoustic Excitation;
- Acoustic Impedance;
- Engine Noise;
- Noise Reduction;
- Porous Walls;
- Turbojet Engines;
- Acoustic Propagation;
- Acoustics;
- Reynolds Number;
- Sound Waves;
- Acoustics