Gas Turbine Fan Diameter Ratio for Core Bending Stiffness
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Solution Overview
Problem
Large gas turbine engines face structural challenges due to increased bending loads and stiffness issues, particularly with larger fan diameters, which can lead to deformation and reduced efficiency, especially when fan outlet guide vanes move rearward, exacerbating core bending.
Innovation Solution
The gas turbine engine design incorporates specific relative component positions and configurations, including a first flange connection downstream of the axial midpoint between the compressor blades, a gearbox-driven fan with a gear ratio between 3.1 and 4.0, and a nacelle with a fan outlet guide vane, to enhance engine core stiffness and manage increased bending loads without deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the fan diameter of a gas turbine engine is increased, then the thrust and efficiency of the engine is improved, but the bending loads and stress on the engine core and supporting components are deleteriously increased
Solution Approach 1:
The patent applies parameter changes by optimizing the axial position of the first flange connection relative to the compressor blades. Specifically, the flange connection is positioned at an axial location that is 0.1 to 0.3 times the axial length of the compressor blades upstream from the trailing edge of the most downstream aerofoil of the first compressor. This parameter optimization allows the engine to accommodate larger fan diameters while managing the increased bending loads through improved structural load distribution.
2Productivity
If the fan size is increased, then the engine performance is improved, but the bending loads on the engine core are deleteriously increased leading to potential deformation
Solution Approach 1:
The patent utilizes parameter changes by defining specific geometric relationships between the flange connection position and compressor blade dimensions. The axial position parameter is set as a ratio (0.1 to 0.3 times the axial length) rather than a fixed dimension, allowing the design to scale with different engine sizes while maintaining optimal structural characteristics for minimizing deformation under bending loads.
Solution Approach 2:
The patent applies local quality by focusing the structural reinforcement specifically at the flange connection region. Rather than uniformly strengthening the entire engine core, the design optimizes the local geometry at the critical flange connection point where the bypass duct meets the engine core, making the structure more efficient at resisting bending loads in the specific region where they are most critical.
3Productivity
If fan outlet guide vanes are moved rearward to improve airflow, then the engine efficiency is improved, but the core bending is exacerbated
Solution Approach 1:
The patent addresses this contradiction by optimizing the axial position parameter of the flange connection. By positioning the flange connection at 0.1 to 0.3 times the axial length of the compressor blades upstream from the trailing edge, the design creates a structural configuration that can accommodate rearward-moving fan outlet guide vanes while maintaining adequate resistance to the increased bending forces through improved load path geometry.
Data Source
AI summary
A gas turbine engine includes an engine core and a fan located upstream of the engine core. The engine core includes: a compressor system including first, lower pressure compressor, and second, higher pressure compressor; and an outer core casing surrounding the compressor system and including a first flange connection arranged to allow separation of the outer core casing at an axial position of the first flange connection. The first flange connection is the first flange connection that is downstream of an axial position defined by the axial midpoint between the mid-span axial location on the trailing edge of the most downstream aerofoil of the first compressor and the mid-span axial location on the leading edge of the most upstream aerofoil of the second compressor. A fan diameter ratio of:firstflangeradiusfandiameteris equal to or greater than 0.125.