Ultra-linear pure wire mesh liner: The broad-Mach-band attenuation concept

While contemporary research primarily targets broadband attenuation at a specific, fixed Mach number, modern regulations mandate stringent noise limits across diverse flight phases characterized by varying Mach numbers. This requirement renders attenuation effectiveness across the Mach number range as critical as broad-frequency-band attenuation. However, the Conventional Perforated Liners (CPL) are challenged by this critical requirement, as their highly flow-dependent impedance may deviate from the optimum value under varying flow conditions, thereby compromising noise reduction across the entire flight envelope. To this end, this work introduces a broad-Mach-band attenuation concept and examines a Pure Wire Mesh Liner (PWML) as a structural realization of this concept, constructed by replacing the perforated facesheet with a sintered dual-layer wire mesh featuring micro-scale apertures. To illustrate its advantages, the evolution of the optimum impedance and the sensitivity of attenuation performance are first analyzed via a finite-element model abstracted from aft nacelles. Three liners, including a PWML, a CPL and a Wire Mesh Perforated Liner (WMPL), are designed for this target, and subsequent experiments reveal that the PWML exhibits the advantage of superior impedance linearity. Moreover, the former leads to a lower sensitivity of the impedance to M_a and thus a closer alignment with the optimum impedance trend, so that the PWML achieves a notable improvement in transmission loss across a very broad M_a range, outperforming the other two.