Three-Bearing Core Shaft Layout for Gas Turbine Resonance Control
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Solution Overview
Problem
Gas turbine engines face challenges in managing vibrational modes and resonance effects due to the length and weight of the core shaft, which can lead to damage during operation, especially when scaled up, as the increased length results in resonance frequencies within the engine's running range.
Innovation Solution
The solution involves optimizing the positioning and stiffness of bearings supporting the core shaft, specifically arranging the minor span between rearward bearings within a controlled range to avoid primary resonances and reduce whirl mode displacements, while maintaining efficient engine operation by ensuring the core shaft's length and bearing stiffness are aligned to prevent resonance-induced damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the core shaft length is increased to support larger engine scales, then the engine size and power output are improved, but the resonance frequency enters the running range causing vibrational damage
Solution Approach 1:
The patent changes the physical parameters of the bearing support system by optimizing the minor span distance between rearward bearings and adjusting bearing stiffness values. This modifies the natural frequency of the core shaft system to move resonance peaks outside the operational speed range, allowing larger engine scales without vibrational damage
Solution Approach 2:
The patent preemptively designs the bearing support system with specific stiffness characteristics and spacing arrangements before operation begins. By pre-configuring the minor span and bearing properties, the system is prepared to avoid resonance conditions that would otherwise cause damage during operation
2Reliability
If the minor span between rearward bearings is reduced to avoid resonance, then vibrational modes are managed, but the bearing stiffness requirements increase
Solution Approach 1:
The patent establishes specific parameter ranges for bearing stiffness (30-100 kN/mm) and minor span dimensions that work together as a system. By coordinating these parameters rather than optimizing them independently, the design achieves vibrational control without excessive bearing stiffness requirements
Solution Approach 2:
The patent applies different bearing stiffness characteristics to different locations along the core shaft. The rearward bearings have specific stiffness requirements that differ from other bearing positions, allowing localized optimization that manages vibrational modes while maintaining overall system feasibility
3Stability of the object's composition
If the bearing stiffness is increased to reduce whirl mode displacements, then shaft stability is improved, but the bearing complexity and manufacturing difficulty increase
Solution Approach 1:
The patent defines specific stiffness parameter ranges (0.08 to 0.5 kN/mm² for the stiffness ratio) that achieve shaft stability without requiring excessively complex bearing configurations. These parameter specifications provide clear design guidance that balances performance with manufacturability
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 approach effectively manages vibrational modes and reduces the risk of damage by shifting resonance frequencies away from the engine's operational range, enhancing the durability and efficiency of the gas turbine engine.
Implementation Method 1
reducing damage to the engine in use caused by whirl mode displacements of the core shaft
Implementation Method 2
managing vibrational modes and resonance effects due to the length and weight of the core shaft
Data Source
AI summary
A gas turbine engine for an aircraft has an engine core including a turbine, a compressor, and a core shaft connecting the turbine to the compressor, the turbine being the lowest pressure turbine of the engine and the compressor being the lowest pressure compressor of the engine; a fan located upstream of the engine core; and a gearbox that receives an input from the core shaft and outputs drive to the fan. The engine core further has three bearings arranged to support the core shaft, and two rearward bearings, and wherein the forward most rearward bearing has a bearing stiffness defined by the radial displacement caused by the application of a radial force at the axial centerpoint of the bearing, and wherein a stiffness ratio of the bearing stiffness at the forward most rearward bearing to the minor span is in the range from 0.08 to 0.5 kN/mm2.