CMC Vane Platform Detuning for Modal Excitation Control
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Solution Overview
Problem
CMCs in airfoils face unique challenges due to susceptibility to modal excitation, particularly at interlaminar interfaces, leading to reduced durability and distress from vibrations during engine operation.
Innovation Solution
Adjusting the design geometry of CMC vane platforms by detuning the modal excitation response through reducing the overhang distance and incorporating chevrons, ensuring the natural frequency is substantially different from the external engine operation excitation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC materials are used in airfoils to achieve high temperature resistance, then temperature capability is improved, but susceptibility to modal excitation and vibrations increases
Solution Approach 1:
The patent applies parameter changes by modifying the platform geometry parameters (overhang distance, chevron configuration) to alter the natural frequency of the CMC vane. This detuning approach changes the vibrational characteristics of the component to avoid resonance with engine excitation frequencies, thereby reducing modal excitation response and improving durability while maintaining the high temperature capability of CMC materials
2Reliability
If the platform overhang distance is reduced to detune modal excitation, then durability is improved, but the platform structural length is reduced
Solution Approach 1:
The patent modifies the geometric parameter of the platform overhang distance to change the natural frequency of the structure. By reducing the overhang distance, the structure is detuned from resonant frequencies, reducing vibrational stress and improving durability. This parameter change directly addresses the contradiction by accepting a shorter platform length to achieve better reliability
3Reliability
If chevrons are incorporated into the platform to eliminate corners, then modal excitation response is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent introduces chevron features that create asymmetric geometry in the platform structure. These chevrons eliminate corner regions that are prone to stress concentration and modal excitation. While the asymmetric chevron features increase manufacturing complexity compared to a simple rectangular platform, they significantly reduce modal excitation response and improve the reliability of the CMC vane
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 detuned platform design reduces modal excitation response, enhancing durability and reducing distress in CMC vane segments by providing a more uniform mass balance and lower deflection amplitudes.
Implementation Method 1
A modal excitation response of the platform is determined based upon an external engine operation excitation frequency. If the modal excitation response is greater than a target modal excitation response, the design geometry of the platform is adjusted to be detuned with the external engine operation excitation frequency
Data Source
AI summary
A method is disclosed for a design geometry of a ceramic matrix composite (CMC) vane arc segment that has a platform and an airfoil section that extends off of the platform. The platform defines an axially trailing face, an axially leading face that is circumferentially offset from the axially trailing face, and first and second circumferential faces. In the method, a modal excitation response of the platform is determined based upon an external engine operation excitation frequency. If the modal excitation response is greater than a target modal excitation response, the design geometry of the platform is adjusted to be detuned with the external engine operation excitation frequency by reducing an overhang distance of the platform in which the modal excitation response at the external engine operation excitation frequency is equal to or lower than the target modal excitation response.