Analytical study on damping characteristics of a perforated liner using an optimized acoustic impedance model

Abstract

Mitigation of thermoacoustic instabilities in gas turbine engines is crucial. Perforated liners offer effective passive acoustic damping; however, the predictive accuracy of existing acoustic impedance models, particularly under diverse flow conditions and at low frequencies, presents an ongoing challenge. This study introduces an improved acoustic impedance model for perforated liners, building upon the comprehensive framework of the Elnady model. The proposed modification specifically targets known limitations in cavity impedance representation at low frequencies by replacing the conventional cotangent function with a cosine function, which offers a more physically consistent description of acoustic reactance in backed cavities. Additionally, selected bias and grazing flow terms are refined based on established formulations to enhance predictive capability under complex flow interactions. The efficacy of the model in predicting dissipation coefficients is rigorously evaluated against published experimental data from benchmark studies, covering a wide range of liner geometries and flow conditions. Results demonstrate that the modified Elnady model provides enhanced predictive accuracy over the original Elnady model and other existing models (Jing, Bauer, and Betts), particularly in capturing peak dissipation trends and behaviors at low frequencies and under combined bias- and grazing-flow scenarios. The physical basis for these improvements is discussed, linking the model formulation to its ability to better represent key acoustic phenomena. These findings offer a refined tool for acoustic liner design, contributing to more effective combustion noise control and stability in gas turbine combustors.