Annular Combustion Chamber Sector Design for Turbomachine Thermal Stress
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Solution Overview
Problem
The existing annular combustion chamber designs face issues with thermomechanical stresses due to differences in expansion coefficients between ceramic wall materials and metal components, leading to potential cracks and inefficient cooling, and the use of flexible fixing lugs results in poor dynamic behavior and increased air infiltration, causing polluting emissions.
Innovation Solution
The combustion chamber is segmented into adjacent sectors that are rigidly attached to the chamber bottom and flanges, with overlapping side edges to control air passage and a radial clearance allowing controlled air entry for cooling, which adapts to thermal expansion and improves cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If flexible fixing lugs are used to connect the bottom of the chamber to the walls, then the difference in expansion between ceramic walls and metal components is accommodated, but the dynamic behavior becomes poor and vibrations increase
Solution Approach 1:
The combustion chamber is divided into multiple radial sectors (at least two) that are independently attachable to the bottom and flanges. This segmentation allows each sector to independently accommodate thermal expansion differences between ceramic walls and metal components while maintaining overall structural integrity and dynamic performance.
2Adaptability or versatility
If flexible fixing lugs are used to connect the walls to casings, then expansion differences are accommodated, but spaces remain at the bottom where fresh air rushes in, degrading combustion efficiency
Solution Approach 1:
The chamber is segmented into multiple radial sectors with overlapping side edges, eliminating gaps at the bottom where fresh air would otherwise rush in. This segmentation maintains combustion efficiency while allowing each sector to independently adapt to thermal expansion.
Solution Approach 2:
The overlapping side edges of adjacent sectors create localized air control zones. The radial clearance between sectors is positioned to allow controlled air entry for cooling while preventing uncontrolled air rush into the combustion chamber, thus maintaining combustion efficiency.
3Temperature
If multi-perforations are made in the walls to cool the inner faces, then cooling efficiency increases, but the cost price increases and mechanical damage characteristics are reduced
Solution Approach 1:
The cooling function is extracted from the wall structure itself and transferred to the radial clearance between sectors. This allows cooling air to flow through the clearance rather than requiring numerous perforations in the walls, thereby reducing manufacturing cost and maintaining mechanical strength.
Solution Approach 2:
The radial clearance between sectors acts as an intermediary cooling passage, replacing the need for direct wall perforations. This intermediary structure provides effective cooling while avoiding the structural weaknesses and cost increases associated with multi-perforations.
4Temperature
If the walls are made of ceramic material, then resistance to high temperatures and mass are improved, but thermomechanical stresses cause cracks in the attachment flanges or walls
Solution Approach 1:
The combustion chamber is divided into multiple radial sectors that can independently expand and contract. This segmentation allows each ceramic wall section to accommodate thermal expansion differences with metal components without generating excessive thermomechanical stresses that would cause cracks.
Solution Approach 2:
The design changes the geometric parameters of the wall structure by introducing radial segmentation with overlapping edges. This parameter change allows the ceramic walls to undergo controlled deformation during thermal cycles while maintaining structural integrity and preventing crack formation.
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 reduces thermomechanical stresses, enhances dynamic behavior, and improves cooling efficiency by controlling air flow, thereby reducing polluting emissions and increasing the surface area benefiting from cooling, while maintaining structural integrity.
Implementation Method 1
A certain volume of fresh air must therefore reach these faces... a radial clearance (i.e. in a direction perpendicular to the axis to the axis of rotation of the turbomachine) between two adjacent sectors which overlap, this clearance allowing the passage of air costs from the outside to the inside of said chamber in order to cool the internal face of at least one of the sectors
Implementation Method 2
the ceramics used to make the walls often have a coefficient of expansion approximately three times lower than that of the metallic materials used to make the bottom of the chamber and said flanges... these lugs being able to deform elastically according to the difference in expansion between these parts
Implementation Method 3
The sectors of the walls are provided with side edges and the side edges of two adjacent sectors overlap, so as to limit the passage of fresh air, between the sectors, from the outside towards the inside of the combustion chamber
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
The combustion chamber (24), having inner and outer walls and a base (30) at the chamber's upstream end, and two metal coupling flanges (27, 29) for connecting the walls to other engine components, has the two walls divided into a number of sectors (126, 128) that are attached to the base of the chamber or to one of the flanges at two or more points (36, 36'). The lateral edges (128a) of the sectors, which are made from a composition material with a ceramic matrix, are inclined circumferentially relative to the main axis of the engine, and each one has a raised lip (60) creating an overlap that leaves a gap for cool air to enter the chamber from the outside.