Gas Turbine Outer Core Casing Stiffness Design
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Solution Overview
Problem
Aircraft gas turbine engines with high Overall Pressure Ratio (OPR) and bypass ratios face challenges in maintaining structural stiffness, leading to potential flexing and rotor blade tip issues, which can result in damage or efficiency losses, and increasing engine weight to address these issues detracts from fuel efficiency gains.
Innovation Solution
The design incorporates a compressor system with a low pressure compressor coupled to a low pressure shaft and a high pressure compressor coupled to a high pressure shaft, with a reduction gearbox connecting the fan to the low pressure shaft, and a structurally efficient outer core casing arrangement that provides a stiff and lightweight structure by maintaining a specific radius ratio between the core casing and fan, reducing bending loads and allowing for reduced core rotor tip clearances.
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 length increases and structural stiffness deteriorates
Solution Approach 1:
The engine core is segmented into multiple functional sections with distinct casing structures. The outer core casing arrangement is divided into a first outer core casing and a second outer core casing spaced radially outwardly, creating a modular structure that can be optimized independently for both length and stiffness requirements
Solution Approach 2:
The solution transitions from solely increasing compressor stages (one-dimensional approach) to utilizing radial dimension by positioning the second outer core casing at a radius greater than 0.25 times the fan radius. This dimensional change allows achieving high OPR while maintaining structural stiffness through increased radial span rather than axial length
2Weight of moving object
If the engine core diameter is reduced to decrease weight, then fuel efficiency is improved, but structural stiffness deteriorates leading to increased flexing
Solution Approach 1:
The outer core casing arrangement utilizes curved and radially distributed structural geometry. The second outer core casing is positioned at a specific radial distance greater than 0.25 times the fan radius, creating a curved structural path that increases moment of inertia and stiffness while minimizing weight compared to a straight axial extension
3Stability of the object's composition
If additional bracing is used to increase engine core stiffness, then structural stability is improved, but engine weight increases
Solution Approach 1:
The second outer core casing serves multiple functions simultaneously: it provides structural stiffness to prevent engine core flexing, defines the core working gas flow path together with the inner core casing, and positions the high pressure compressor components. This multi-functionality eliminates the need for separate bracing structures that would add weight
Data Source
Figure 1~2
Figure 3
Figure 4a~4b
AI summary
An aircraft gas turbine engine (10) comprises 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). An inner core casing (34) is provided radially inwardly of compressor blades (42) of the compressor system. A fan (13) is coupled to the low pressure shaft (24) via a reduction gearbox (14). The high pressure compressor (16) comprises an outer core casing arrangement provided radially outwardly of compressor blades of the high pressure compressor (16), the inner core casing (34) and outer core casing arrangement defining a core working gas flow path (B) therebetween; and the outer core casing arrangement comprises a first outer core casing (48) and a second outer core casing (50) spaced radially outward from the first outer core casing (48). At an axial plane of an inlet (E) to the high pressure compressor (16), the second outer core casing (50) has a radius greater than 0.25 times a radius of the fan (13).