Gas Turbine Engine Core Casing Stiffness Design
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Solution Overview
Problem
High Overall Pressure Ratio (OPR) and high bypass ratio gas turbine engines are susceptible to flexing in flight, leading to potential rotor blade tip damage and reduced efficiency due to excessive blade tip clearances, and increasing stiffness through additional bracing results in weight penalties.
Innovation Solution
The design incorporates a compressor system with a low pressure compressor and high pressure compressor coupled to respective shafts, an inner and outer core casing arrangement that bifurcates to provide a stiff and structurally efficient structure, reducing bending and flexing, and a reduction gearbox to maintain alignment and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of compressor stages is increased to achieve high Overall Pressure Ratio (OPR), then thermodynamic efficiency is improved, but the engine core becomes longer and more susceptible to flexing
Solution Approach 1:
The patent introduces a second outer core casing that is radially outwardly spaced from the first outer core casing, creating a multi-layered radial structure. This dimensional approach (adding radial layers rather than just extending axially) allows the engine to achieve high OPR through compact axial design while the second outer casing provides enhanced structural stiffness to prevent flexing.
Solution Approach 2:
The patent employs a composite casing structure with an inner core casing, first outer core casing, and second outer core casing arranged in concentric layers. This composite arrangement combines the functions of different casings (structural support, aerodynamic flow paths, and stiffness provision) to achieve both high efficiency and structural stability.
2Stability of the object's composition
If additional bracing is used to increase engine core stiffness, then flexing is reduced, but engine weight increases
Solution Approach 1:
The second outer core casing serves multiple functions simultaneously: it provides structural stiffness to reduce flexing, contains the core working gas flow path, and supports the overall engine structure. This multi-functionality eliminates the need for separate additional bracing components, thereby avoiding weight penalties while achieving the required stiffness.
3Use of energy by moving object
If high bypass ratio is used to improve efficiency, then fuel consumption is reduced, but rotor blade tip clearances increase leading to potential damage
Solution Approach 1:
The patent divides the outer core casing into two separate casings (first and second outer core casings) that are radially spaced apart. This segmentation allows independent optimization of each casing's function, with the second outer casing specifically positioned to provide structural support that maintains rotor blade tip clearances, thereby preventing damage while allowing high bypass ratio operation.
Data Source
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AI summary
An aircraft gas turbine engine (10) includes a compressor system comprising a low pressure compressor (15) coupled to a low pressure shaft (23), and a high pressure compressor (16) coupled to a high pressure shaft (24). The engine includes an inner core casing (34) provided radially inwardly of compressor blades (42) of the compressor system, and an outer core casing arrangement provided radially outwardly of compressor blades (42) of the compressor system, the inner core casing and outer core casing arrangement defining a core working gas flow path (B) therebetween. The engine also includes a fan (13) coupled to the low pressure shaft (23) via a reduction gearbox (14); the outer core casing arrangement comprising a first outer core casing (48) and a second outer core casing (50) spaced radially outwardly from the first outer core casing (48). At an axial plane (E) of an inlet to the high pressure compressor (16), the second outer core casing (50) has an inner radius at least 1.4 times the inner radius of the first outer core casing (48).