Epicyclic Gearbox Support Stiffness for Gas Turbine Vibration Control
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Solution Overview
Problem
Designing a gas turbine engine with a larger fan diameter poses challenges in efficiently mounting the gearbox and fan shaft, requiring careful consideration of component properties to achieve optimal efficiency and power output.
Innovation Solution
The engine incorporates an epicyclic gearbox with specific radial bending and tilt stiffness ratios, moment of inertia, and gearbox support structures to isolate the gearbox from loads and minimize vibration, ensuring efficient operation and reduced modal frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a larger fan diameter is used to increase thrust and efficiency, then power output and fuel efficiency are improved, but the complexity of mounting the gearbox and fan shaft increases
Solution Approach 1:
The patent applies parameter changes by optimizing the radial bending stiffness to moment of inertia ratio within a specific range (2.5×10^-2 to 6.0 Nkg^-1 m^-3) and the tilt stiffness to moment of inertia ratio (4.0×10^-4 to 2.7×10^-1 Nrad^-1 kg^-1 m^-1). These parameter optimizations enable the gearbox support structure to effectively manage the increased loads from larger fan diameters while maintaining manageable mounting complexity.
2Object-generated harmful factors
If the radial bending stiffness of the gearbox support is increased to reduce vibration, then vibration is reduced, but the torsional shear stress on the support increases
Solution Approach 1:
The patent resolves this contradiction through parameter changes by defining specific ratio ranges: radial bending stiffness to moment of inertia (2.5×10^-2 to 6.0 Nkg^-1 m^-3) and tilt stiffness to moment of inertia (4.0×10^-4 to 2.7×10^-1 Nrad^-1 kg^-1 m^-1). These optimized parameters enable the support structure to reduce vibration while keeping torsional shear stress within acceptable limits (less than or equal to 4.90×10^8 N/m^2 at maximum take-off conditions).
Solution Approach 2:
The patent applies dynamics by making the stiffness properties adjustable within defined ranges rather than fixed values. The radial bending stiffness and tilt stiffness can be optimized based on specific operational requirements, allowing the system to adapt between vibration reduction and stress management depending on the operating conditions.
3Stability of the object's composition
If the tilt stiffness of the gearbox support is increased to improve stability during maneuvering, then stability is improved, but the modal frequencies of the system increase
Solution Approach 1:
The patent applies parameter changes by optimizing the tilt stiffness to moment of inertia ratio within the range of 4.0×10^-4 to 2.7×10^-1 Nrad^-1 kg^-1 m^-1. This parameter optimization enables the system to achieve adequate stability during maneuvering while controlling modal frequencies within acceptable ranges, preventing excessive stiffness that would lead to overly high natural frequencies.
Data Source
AI summary
A gas turbine engine for an aircraft including an engine core including a turbine, compressor, and core shaft connecting the turbine and compressor; a fan located upstream of the engine core including a plurality of fan blades; a gearbox that can receive input from the core shaft and can output drive to the fan at a lower rotational speed than the core shaft, an epicyclic gearbox including a sun gear, planet gears, a ring gear, and a planet carrier on which the planet gears are mounted; and a gearbox support. A first gearbox support shear stress ratio:torsionalshearstressofthegearboxsupportatmaxiumumtakeoffconditionsradialbendingstiffnessofthegearboxsupportis less than or equal to 4.9×101 m−1, and/or a second gearbox ratio:torsionalshearstressofthegearboxsupportatmaximumtakeoffconditionstiltstiffnessofthegearboxsupportis less than or equal to 4.1×103 rad/m3.