Composite Flame Holder Arm Mounting for Turbofan Afterburners
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Solution Overview
Problem
Flame holder arms in turbofan engines made of ceramic matrix composite materials face issues with thermal expansion differences from metal casings, leading to heat clamping loss and stress generation, which reduces their lifespan due to the fragility of folded fibers and high stress on metal support joints.
Innovation Solution
The design incorporates bolts with spring washers to maintain tightening despite expansion differences, uses bosses for airtight cavity crossing, and features a divergent angle in the arm support to limit axial movement, along with a swivel connection for the ventilation tube, reducing stress on composite materials and allowing for easier assembly and disassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If CMC arms are fixed directly to metal casing, then weight is reduced and temperature resistance is improved, but thermal expansion differences cause heat clamping loss and stress generation
Solution Approach 1:
The arm is divided into modular sections with cavities that can be independently assembled and disassembled, allowing for maintenance and replacement without affecting the entire structure
Solution Approach 2:
A mounting device with bolts and spring washers acts as an intermediary between the CMC arm and metal casing, accommodating thermal expansion differences and preventing direct stress transmission
2Ease of manufacture
If flanges are bent to fix arm to casing, then connection is achieved, but fiber folding occurs causing fragility and reduced lifespan
Solution Approach 1:
The arm structure is segmented with flat upper parts that can be independently mounted using bolts, eliminating the need for bent flanges and fiber folding
Solution Approach 2:
Mechanical fastening using bolts and spring washers replaces the fiber folding mechanism, providing a more reliable connection that accommodates thermal expansion
3Ease of manufacture
If bolts are used to fix arm to support, then connection is achieved, but thermal expansion differences cause loss of heat clamping
Solution Approach 1:
The spring washers provide dynamic adjustment capability, allowing the bolt connection to accommodate thermal expansion and contraction while maintaining consistent clamping force
Solution Approach 2:
The design explicitly accounts for thermal expansion by using spring washers that can compress and extend to maintain clamping force during temperature cycles
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 configuration enhances the mechanical strength and lifespan of flame holder arms by eliminating fiber bending and reducing thermal stresses, while facilitating air supply regulation and simplifying the manufacturing process.
Implementation Method 1
the large difference in expansion between the CMC arm and the metal casing can cause a loss of heat clamping between the 2 parts
Implementation Method 2
a ventilation tube whose role is to cool on the one hand the metal walls of the arm bathed in the primary flow, and on the other hand the injector with air coming directly from the cold flow
Implementation Method 3
The injector-tube assembly is itself protected from the radiation of the flame by another metal part, the thermal protection screen
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
Flame-holder device for afterburner of a turbofan, said turbofan comprising a first inner annular casing (3) and a second inner annular casing (5), these defining a passage (4) for a primary flow, and an outer annular casing (2) defining with said first inner annular casing (3) a passage (1) for a secondary flow, comprising at least one arm-supporting means (8) made of metallic material designed to be fixed to said outer casing (2) by means of an upper plate (9) and at least one flame-holder arm (7) that consists of a one-piece structure of composite material comprising two mutually attached walls (28a, 28b) arranged in such a way as to define a groove whose profile is approximately a V, said walls supporting, on their upper part situated in the secondary flow (31a, 31b), fixing means (34a, 34b) for fixing to said arm-supporting means (8), said device being characterized in that said upper parts (31a, 31b) are approximately planar and are positioned facing each other.