Grid-Pattern Flutter Damper for Gas Turbine Nacelle
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Solution Overview
Problem
Geared turbofan architectures with low pressure ratio fans are susceptible to fan flutter, an aeromechanical instability that can be detrimental to fan blade life, and existing solutions are inadequate for integrating effective flutter dampers into the limited space of propulsion systems.
Innovation Solution
A flutter damper system comprising an acoustic liner with a grid pattern of chambers configured for peak acoustical energy absorption at specific frequency ranges associated with fan flutter modes, integrated into the nacelle of a gas turbine engine, allowing for efficient absorption of acoustic energy and mitigation of fan flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional flutter dampers are used, then fan flutter can be suppressed, but the available space in the nacelle is insufficient for integration
Solution Approach 1:
The flutter damper is segmented into multiple functional layers including an acoustic liner with resonant chambers, a porous absorber layer, and a flow surface. Each layer performs a specific function: the acoustic liner targets specific flutter frequencies through resonant chambers, the porous layer provides broadband absorption, and the flow surface maintains aerodynamic compatibility. This segmentation allows the system to achieve effective flutter suppression while optimizing space utilization through specialized functional zones.
Solution Approach 2:
The patent utilizes the radial dimension of the nacelle by positioning the acoustic liner and resonant chambers in the radial direction between the fan and the nacelle wall. The resonant chambers extend radially outward from the acoustic liner, effectively using the available radial space. Additionally, the flow surface is designed to conform to the nacelle's external contours, utilizing the circumferential and axial dimensions to maximize integration within the limited nacelle volume.
2Loss of energy
If the acoustic liner is made larger to improve flutter damping, then acoustic energy absorption increases, but the device complexity and integration difficulty increase
Solution Approach 1:
The acoustic liner is designed with local variations in chamber geometry, spacing, and tuning frequencies to target specific flutter modes at different locations. The resonant chambers are strategically positioned and sized to match the spatial distribution of flutter modes, with larger chambers positioned to target stronger flutter sources. This localized optimization allows effective energy absorption without requiring a uniformly large structure throughout the entire nacelle.
Solution Approach 2:
The patent employs a nested structure where the acoustic liner with resonant chambers is integrated within the nacelle wall structure, and the flow surface is positioned as the outermost layer conforming to the nacelle contours. The resonant chambers are nested within the acoustic liner, which itself is nested within the nacelle structure. This nesting approach maximizes space utilization and simplifies integration by combining multiple functions within a compact hierarchical structure.
3Adaptability or versatility
If multiple chambers are added to cover different flutter modes, then frequency range coverage improves, but the manufacturing and assembly difficulty increases
Solution Approach 1:
The acoustic liner is divided into multiple modular sections, each containing resonant chambers tuned to specific frequency ranges. These modular sections can be manufactured independently and then assembled in sequence to achieve the desired overall frequency coverage. Each module contains chambers of varying sizes and geometries to target different flutter modes, allowing the system to cover a broad frequency spectrum while maintaining manufacturing simplicity through standardization of modular components.
Solution Approach 2:
The patent combines different chamber configurations and acoustic materials within the acoustic liner to create a composite structure that addresses multiple frequency ranges. The acoustic liner integrates resonant chambers with specific tuning frequencies, porous absorber materials, and flow surface treatments in a unified composite structure. This composite approach allows simultaneous targeting of multiple flutter modes while maintaining a unified manufacturing process and assembly procedure.
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 absorbs acoustic energy at targeted frequencies, preventing fan flutter and enhancing the fan flutter margin without requiring inlet redesign, while being lightweight and scalable for integration into optimized propulsion systems.
Implementation Method 1
configured for peak acoustical energy absorption at a frequency range that is associated with a first fan flutter mode
Implementation Method 2
absorbing the acoustic energy associated with the flutter structural mode
Implementation Method 3
preventing the fan from fluttering, and which may be integrated into the reduced available space
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
Disclosed is a flutter damper (102) including a first plurality of chambers (318) configured for peak acoustical energy absorption at a frequency range that is associated with a first fan flutter mode, the first plurality of chambers in fluid communication with a flow surface (314), and a second plurality of chambers (320) configured for peak acoustical energy absorption at a frequency range that is associated with a second fan flutter mode, the second plurality of chambers in fluid communication with the flow surface, and wherein the first plurality of chambers and second plurality of chambers are disposed in a grid pattern.