Using Acoustic Liner for Fan Noise Reduction in Modern Turbofan Engines

Abstract

With the increase in global air travel, aircraft noise has become a major public issue. In modern aircraft engines, only a small proportion of the air that passes through the whole engine actually goes through the core of the engine, the rest passes around it down the bypass duct. A successful method of reducing noise further, even in ultra-high bypass ratio engines, is to absorb the sound created within the engine. Acoustically absorbent material or acoustic liners have desirable acoustic attenuation properties and thus are commonly used to reduce noise in jet engines. The liners typically are placed upstream and downstream of the rotors (fans) to absorb sound before it propagates out of the inlet and exhaust ducts. Noise attenuation can be dramatically improved by increasing the area over which a noise reducing material is applied and by placing the material closer to the noise source. In this paper we will briefly discuss acoustic liner applications in modern turbofan engines.

Comparative Concept Study and Evaluation for New Broadband Noise Absorbing Acoustic Liner Concepts for Civil Aviation

“… "--" or 0 point  criteria fulfilment much worse than with the SHR-Liner  "-" or 1 points  criteria fulfilment worse than with the SHR-Liner  "o" or 2 points  criteria fulfilment as good as with the SHR-Liner  "+" or 3 points  criteria fulfilment better than with the SHR-Liner  "++" or 4 points  criteria fulfilment much better than with the SHR-Liner Figure 5 shows the degree of criteria fulfilment , by the FHR-and PR-Liner in comparison to the reference liner (SHR-Liner). The selection of the degree of implementation in Figure 5 was made by information from  the state of the art [27], [28], [29],  investigations on the principles of action [03], [18],  analyses of system safety and aspects of integration in the aero engine [15], [30]  research of technical literature [31], [32], [33] and  information exchange of project partners from different technical disciplines.…”

Algorithms and analyses for stochastic optimization for turbofan noise reduction using parallel reduced-order modeling

“…where p(x, ϑ) satisfies the weak equation (2). The minimization is over the physical domain of ξ which is omitted for simplicity.…”

Low-frequency interior noise in prop-driven aircrafts: Sources and control methodologies

“…Aircraft noise emissions reduction has become a driving factor for competitive aircraft design, as political and environmental laws have become more firm. [1][2][3][4] Noise reduction techniques can be broadly classified as passive and active methods. Passive control involves reducing the radiated noise by energy absorption, while the active method involves reducing source strength or modifying acoustic field in the duct to obtain noise reduction.…”