A Transmission Line Impedance Prediction Model for Acoustic Liners

A Zwikker and Kosten Transmission Line model is used to predict the acoustic impedance at the surface of an acoustic liner. Multiple versions of this model, labeled as ZKTL, have been used at the NASA Langley Research Center for five decades. The latest version (titled ZKTL-SC) is presented, including descriptions of component models to compute sound transmission through different types of layers that might constitute an acoustic liner. This model computes the sound transmission from the backplate to the surface of a single chamber of the liner. Results for multiple chambers can then be combined to compute an effective (smeared) impedance over their combined surfaces. Multiple updates are included in this version. A “single channel” model enables focus on the physics of individual chambers that comprise the entire acoustic liner. This allows a more unified modeling approach to be applied. An updated model is used to account for the effects of thick partition between adjacent liner chambers, a feature that has become more prevalent with the advent of additively manufactured liners. Implementation of chambers filled with bulk material has also been updated to use a similar modeling approach to that employed with local-reacting liners. Finally, experimental results have been compiled to support validation of each of the models used for the variety of chamber types considered.