Inlet Deep Cavity Flutter Liner Plenum Design
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Solution Overview
Problem
Modern aircraft engines produce low-frequency noise and coupled aeroelastic vibrations due to fan operation, which affect cabin comfort and require effective noise attenuation solutions.
Innovation Solution
A sound-absorbing arrangement for the engine nacelle featuring an acoustic liner with a shroud defining a plenum in fluid communication with the liner's core, providing a lightweight and cost-effective solution for noise attenuation, where the shroud is bonded or fastened to the liner and attachment ring, forming a non-structural component to minimize mechanical loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional acoustic liner is used without a shroud-defined plenum, then the noise attenuation capability is limited, but the structure remains simpler and lighter
Solution Approach 1:
The acoustic liner is segmented into multiple modular units, each with its own shroud-defined plenum. This allows the noise attenuation function to be distributed across multiple independent modules, improving overall effectiveness while maintaining ease of installation and replacement. The segmentation enables targeted noise control at different locations within the nacelle inlet.
Solution Approach 2:
The shroud-defined plenum acts as an intermediary chamber between the acoustic liner core and the external environment. This plenum volume enhances the acoustic treatment by providing an additional compliance volume that improves low-frequency noise attenuation, effectively mediating between the solid acoustic liner material and the gaseous noise field.
2Object-affected harmful factors
If a shroud is added to define a plenum, then noise attenuation is enhanced, but the weight and structural complexity increase
Solution Approach 1:
The shroud is constructed as a thin-walled structural component that defines the plenum volume without adding significant mass. This flexible shell approach provides the necessary acoustic containment while minimizing weight penalty, allowing the plenum to achieve effective low-frequency noise attenuation without substantially increasing nacelle inlet assembly weight.
3Strength
If the shroud is rigidly attached to the acoustic liner and attachment ring, then structural integrity is improved, but mechanical loads increase
Solution Approach 1:
The acoustic liner is extracted from the primary load-bearing structure and positioned within the shroud-defined plenum as a non-structural acoustic treatment element. This separation allows the acoustic liner to focus on noise attenuation without bearing mechanical loads, while the shroud and attachment ring provide the necessary structural support independently.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces engine noise and vibrations by creating a plenum that is fluidly connected to the acoustic liner's core, enhancing noise attenuation while maintaining structural integrity and reducing overall nacelle weight.
Implementation Method 1
an acoustic liner disposed radially inward from the attachment ring, the acoustic liner comprising a proximal skin, a distal skin, and a core disposed between the proximal skin and the distal skin
Implementation Method 2
the shroud defines a plenum disposed between the acoustic liner and the shroud, the plenum in fluid communication with the core via perforations in the distal skin
Data Source
AI summary
A nacelle inlet may comprise an aft bulkhead, an attachment ring extending in an aft direction from the aft bulkhead, an acoustic liner disposed radially inward from the attachment ring, the acoustic liner comprising a proximal skin, a distal skin, and a core disposed between the proximal skin and the distal skin, and a shroud extending longitudinally between a forward side of the shroud and an aft side of the shroud and extending circumferentially between a first end of the shroud and a second end of the shroud, wherein the shroud defines a plenum disposed between the acoustic liner and the shroud, the plenum is in fluid communication with the core via perforations in the distal skin. The plenum may serve to attenuate low frequency noise known as “buzz saw” tones and/or alleviate pressure resonance conditions that may cause structural damage to the engine fan blades.