Variable Depth Acoustic Liner for Gas Turbine Noise
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Solution Overview
Problem
Existing acoustic liners for gas turbine engines, such as SDOF and 2DOF liners, face challenges in effectively attenuating noise across varying engine operating conditions due to fixed cell depths and porosity, leading to inefficiencies in noise suppression and increased weight and cost.
Innovation Solution
The development of an acoustic liner with a core layer comprising cavities of variable depth and porosity, achieved through movable backing sheet members that adjust based on engine operating conditions, allowing for active control of cavity volumes and percent open area to optimize noise attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a 2DOF liner with two cellular layers is used to suppress multiple frequencies, then noise attenuation performance is improved, but weight and cost significantly increase
Solution Approach 1:
The patent applies dynamics by making the cell depth variable through movable backing sheets that can adjust the cavity depth in response to changing noise frequencies. This allows a single liner structure to adapt its acoustic properties dynamically, replacing the need for multiple fixed-depth layers while maintaining multi-frequency suppression capability.
Solution Approach 2:
The invention changes the parameter of cell depth from fixed to variable by incorporating movable backing sheets. This parameter change enables the same physical structure to achieve different acoustic resonance characteristics, allowing one liner to perform the function of multiple liners with different cell depths.
2Object-affected harmful factors
If a 2DOF liner with two cellular layers is used to suppress multiple frequencies, then noise attenuation performance is improved, but liner thickness increases
Solution Approach 1:
The movable backing sheets enable dynamic adjustment of cavity depth within a single layer, allowing the liner to achieve multi-frequency suppression without adding additional layers. This dynamic mechanism replaces the static multi-layer approach with a single adaptive layer, reducing overall thickness.
3Object-affected harmful factors
If variable depth construction is implemented in SDOF liner to achieve multiple frequency advantages, then noise attenuation is improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent segments the backing sheet into multiple independently movable sections, each capable of adjusting the depth of adjacent cells. This segmentation allows for simpler manufacturing of each individual segment while achieving variable depth functionality across the entire liner through the coordinated movement of these segments.
Solution Approach 2:
The invention introduces a mechanical dynamic system with movable backing sheets that can be actuated to change cell depths. This dynamic mechanism provides a manufacturable solution compared to complex fixed variable-depth geometries, as it uses straightforward mechanical movement rather than complex molding or fabrication processes.
4Device complexity
If fixed porosity cell walls are used in acoustic liner, then structural simplicity is maintained, but adaptability to changing engine noise conditions is reduced
Solution Approach 1:
The movable backing sheets create a dynamic system where cavity depth can be adjusted in response to changing noise conditions. This maintains relatively simple fixed porosity cell walls while adding the adaptive capability through the movement mechanism, achieving a balance between structural simplicity and adaptability.
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
This solution enables improved noise attenuation across different engine operating conditions, reducing weight and cost while maintaining effective noise suppression, by dynamically adjusting cavity depths and porosity to match changing noise frequencies and wavenumbers.
Implementation Method 1
the cell depth controls the internal volume of the cell that is available for acoustic resonance
Implementation Method 2
Acoustic liners are known to be applied on the internal walls of the engine's casing and hub to attenuate the fan noise propagating through the engine ducts
Data Source
AI summary
Noise attenuation structures, such as acoustic liners for gas turbine engines, are provided. For example, an acoustic liner comprises a face sheet, a backing sheet spaced apart from the face sheet, and a plurality of cavities defined between the face and backing sheets. The cavities are defined by cavity walls. A plurality of backing sheet walls extends from the backing sheet toward the face sheet. The backing sheet walls extend adjacent the cavity walls, and the backing sheet is movable with respect to the face sheet such that the cavities have a variable depth. Other embodiments of noise attenuation structures also are provided.