Flutter Damper Acoustic Liner for Turbofan Fan Stability
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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 not effectively integrated into the limited space of propulsion systems.
Innovation Solution
A flutter damper comprising an acoustic liner with a perforated radial inner face sheet and a chamber configured for peak acoustical energy absorption at frequencies associated with fan flutter modes, along with stiffening structures that tune the top surface out of the flutter frequency range, allowing for integration into optimized propulsion systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flutter damper is integrated into the nacelle inlet structure, then fan flutter is mitigated, but the available space is reduced
Solution Approach 1:
The flutter damper is nested within the nacelle inlet structure by integrating the acoustic liner and chamber into the existing inlet geometry. The acoustic liner is positioned between the fan and inlet, with the chamber secured to the outer skin of the nacelle, effectively utilizing the existing space without requiring additional external volume.
Solution Approach 2:
The chamber is configured with specific dimensional proportions (width, height, length) to optimize acoustic energy absorption at targeted flutter frequencies. The stiffening structures extend from the front surface to the back surface of the chamber, creating a three-dimensional configuration that tunes the top surface out of the flutter frequency range while maximizing space utilization.
2Reliability
If the acoustic liner and chamber are configured for peak energy absorption at fan flutter frequencies, then flutter is reduced, but the device complexity increases
Solution Approach 1:
The acoustic liner and chamber are configured with specific parameter ranges: the chamber has a width of 0.1-0.3 times the fan outer diameter, height of 0.05-0.15 times the fan outer diameter, and length of 0.2-0.5 times the fan outer diameter. The stiffening structures have specific proportions relative to chamber dimensions, creating a standardized configuration that achieves peak energy absorption at targeted flutter frequencies while maintaining manufacturability.
Solution Approach 2:
The stiffening structures are strategically positioned on the chamber to tune specific regions (the top surface) out of the flutter frequency range. The first and second stiffening structures are arranged to divide the top surface into substantially equal portions, creating localized structural modifications that target specific acoustic modes without requiring complex modifications throughout the entire structure.
3Reliability
If stiffening structures are added to tune the top surface out of flutter frequency range, then flutter mitigation is enhanced, but manufacturing complexity increases
Solution Approach 1:
The stiffening structures are designed with specific parameter relationships to chamber dimensions, creating a scalable design that can be manufactured using standard processes. The structures extend from the front surface to the back surface of the chamber with proportions based on chamber width and height, allowing for consistent manufacturing across different engine sizes while achieving the desired acoustic tuning.
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 mitigates fan flutter by providing peak energy absorption and impedance characteristics within targeted frequency ranges, enhancing fan stability without requiring inlet redesign and offering a lightweight, scalable, and retrofittable solution.
Implementation Method 1
the acoustic liner being configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter; and a chamber secured to the radial outer back sheet, the chamber being in fluid communication with the acoustic liner, and the chamber being configured for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes
Implementation Method 2
at least one stiffening structure connected to a top surface of the chamber that tunes the top surface out of the frequency range associated with one or more fan flutter modes
Data Source
Figure 1
Figure 2~3
Figure 4A~4B
AI summary
Disclosed is a flutter damper (102), including an acoustic liner (101) having a perforated radial inner face sheet (108) and a radial outer back sheet (110), the acoustic liner being configured for peak acoustical energy absorption at a frequency range that is greater than a frequency range associated with fan flutter, a chamber (118) secured to the radial outer back sheet, the chamber being in fluid communication with the acoustic liner, and the chamber being configured for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes, and at least one stiffening structure (132, 134) connected to a top surface of the chamber that tunes the top surface out of the frequency range associated with one or more fan flutter modes.