Acoustic Liner Bypass Cooling for Noise Attenuation
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Solution Overview
Problem
Acoustic liners in fluid handling ducts, such as those in gas turbine aircraft engines, face challenges in attenuating low-frequency noise while maintaining durability, as cooling the liners through resonator chambers degrades their noise attenuating properties and reducing resonator necks compromises porosity and durability.
Innovation Solution
The acoustic liner features a bypass coolant passage system that directs coolant around the resonator chamber and neck, maintaining high porosity and acoustic admittance by allowing coolant to flow through perforations without passing through the chamber or neck, thus enhancing durability without impairing noise attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coolant flows through the resonator chamber and neck to cool the liner, then the liner's durability is improved, but the liner's acoustic admittance deteriorates
Solution Approach 1:
The invention divides the cooling function from the acoustic resonance function by creating a separate bypass coolant passage that runs parallel to but independent from the resonator chamber and neck. This segmentation allows coolant to flow through the liner structure for cooling without passing through the acoustic resonator components, thereby maintaining acoustic admittance while achieving cooling durability
Solution Approach 2:
The bypass coolant passage acts as an intermediary pathway that enables coolant flow to reach the liner structure for cooling purposes without directly interacting with the resonator chamber and neck. This intermediary passage mediates between the cooling requirement and the acoustic performance requirement, allowing both to be satisfied simultaneously
2Measurement precision
If the resonator neck size is decreased to tune for low frequency noise, then the resonator can be tuned to low frequency, but the liner's porosity and acoustic admittance are reduced
Solution Approach 1:
The invention separates the cooling function from the acoustic resonance function by creating a dedicated bypass coolant passage. This segmentation allows the resonator neck to be optimized for acoustic performance (maintaining sufficient size for high porosity and acoustic admittance) while the bypass passage handles the cooling flow independently, enabling low frequency tuning without compromising acoustic properties
3Measurement precision
If the resonator chamber volume is increased to attenuate low frequency noise, then low frequency attenuation is improved, but space constraints in aircraft engine ducts are violated
Solution Approach 1:
The invention addresses the volume constraint by utilizing the bypass coolant passage as an additional dimensional solution space. Instead of increasing the resonator chamber volume (which is constrained by duct space), the cooling function is extended into a separate dimensional pathway (the bypass passage), allowing the resonator chamber to maintain its compact size while still achieving low frequency attenuation through optimized neck geometry
4Measurement precision
If the neck length is increased to tune for low frequency noise, then low frequency attenuation is improved, but the liner's acoustic admittance is reduced
Solution Approach 1:
The invention segments the fluid flow path into two independent channels: the resonator neck for acoustic resonance and the bypass coolant passage for cooling. This segmentation allows the neck length to be extended for low frequency tuning without the same negative impact on acoustic admittance, because the bypass passage provides an alternative flow path that compensates for the increased neck length effects
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 design effectively attenuates a broader spectrum of noise frequencies, including low frequencies, while maintaining the liner's durability by avoiding coolant flow through the resonator chamber, thus achieving improved noise reduction without compromising cooling efficiency.
Implementation Method 1
The inter-sheet compartment serves as a resonator chamber for attenuating noise. One well known relationship that describes the noise frequency that a resonator will attenuate is: where c is the local speed of sound, A N is the cross sectional area of the neck leading to a chamber
Implementation Method 2
A bypass coolant passage guides coolant to the perforations without guiding it through the resonator chamber or the neck
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An acoustic liner (20) includes a remote panel (26), a proximate panel (28) transversely spaced from the remote panel (26) and a resonator chamber (34b) residing between the panels (22,26). Perforations (38) penetrate the proximate panel (22) in registration with the resonator chamber (34b). A neck (56) with an inlet (58) recessed from the proximate panel (22) establishes communication between the chamber (34b) and a fluid stream (G) flowing past the proximate panel (22). A bypass coolant passage (66) guides coolant through the perforations (38) without guiding it through the resonator chamber (34b).