1. Field of the Invention
This invention is directed to an assembly, method and system for reducing aircraft noise generated by aircraft engines such as turbofan engines, and to a method of making such an assembly. More particularly, this invention relates to an assembly located in a portion of an aircraft such as a turbofan engine nacelle inlet, engine fan case, core cowl, thrust reverser, core casing, and/or center body. The assembly comprises a core portion having at least one entrance end and at least one exit end for the passage of acoustic energy therethrough. The assembly also comprises a first member having an exterior face and an interior face, wherein the first member is adjacent to at least a portion of the core, and the first member has a plurality of openings therein to permit the passage of acoustic energy therethrough.
2. Background Information
The desirability of reducing the noise generated by aircraft engines such as turbofan engines is well known to those skilled in the art. As disclosed, for example, in U.S. Pat. No. 6,112,514, one method of reducing such noise which has been proposed is the use of Herschel-Quincke (H-Q) tubes of appropriate length arranged in an array about a turbofan engine to reduce the noise levels generated by the engine. Such an array of tubes, if properly located about the engine, creates destructive energy waves that cancel the acoustic energy in the turbofan engine yet do not contribute to any significant aircraft drag or reduced fuel consumption. As is also disclosed in U.S. Pat. No. 6,112,514, various parameters such as tube length, cross-sectional area etc. may be controlled via a control system responsive to varying engine operational or environmental conditions. In such a control system, sound is reintroduced in an out-of-phase relation from the sound propagating from the engine fan to effect sound cancellation. Such a control system may employ feedback or feedforward control, or a combination thereof. WO 02/059474 discloses an assembly and method for reducing such noise using at least one dynamically adaptable H-Q tube which is capable of being dynamically adapted with respect to tube geometry and acoustical characteristics to optimize cancellation of the predominant source tone for different engine cycles.
Existing H-Q tube configurations such as those described in U.S. Pat. No. 6,112,514 and WO 02/059474 are attached to the external surface of aircraft components, and thus are limited to specific shapes which are not always amenable to integration with the structure of the engine. However, it would be useful to employ a noise reduction assembly, which is integrated into the structure of aircraft components such as the turbofan engine nacelle core cowl. Accordingly, the assemblies of this invention may be employed in areas of little or no clearance, such as the core cowl. In contrast, a prior art external H-Q tube cannot be employed within the core cowl, because the external H-Q tube will physically interfere with other components.
In addition, although the use of an array of H-Q tubes within a “passive liner treatment” has previously been disclosed, for example, in U.S. Pat. No. 6,112,514, such a configuration employs an array of tubes which is not substantially contained within the passive liner treatment. In contrast, according to the present invention, the acoustic energy passes through, for example, conduit or conduits which are substantially contained within the core portion, thereby achieving various structural and cost benefits. In addition, U.S. Pat. No. 6,112,514 does not disclose the use of a first member having a plurality of openings therein (such as a perforated skin) which is operatively employed with entrance and exit ends of the core portion to permit the passage of acoustic energy into and out of the conduit. Moreover, in U.S. Pat. No. 6,112,514 a screen is required at the ends of the tubes. In contrast, the assembly of this invention does not employ a screen at the entrance and exit ends of the core portion.
Accordingly, it is one object of this invention to provide a noise reduction assembly which may be integrated within the structure of aircraft components. It is another object of this invention to provide a method of reducing aircraft noise using such an assembly. It is yet another object of this invention to provide an aircraft noise reduction system which employs such an assembly. Other objects, features and advantages of the present invention will be apparent to those skilled in the art from the detailed description of the invention and its various embodiments as described herein.