Geared Turbofan Gearbox Layout for Compact Core Flowpath
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Solution Overview
Problem
Turbofan engine design faces challenges in optimizing flowpath geometry due to competing factors like weight, material strength, and aerodynamics, particularly in bearing arrangements that support rotating structures, which affect engine efficiency and require improved support mechanisms for radial and thrust loads.
Innovation Solution
The design incorporates a splitter along the flowpath with specific radius ratios and bearing configurations, including non-thrust roller bearings and thrust bearings, to manage radial and thrust loads efficiently, while optimizing the placement of hubs and seals to minimize radial turning and enhance overall engine efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a drive gear system is placed axially between the compressor and the fan, then the fan can be driven at a reduced speed with increased torque, but the core flowpath diameter increases
Solution Approach 1:
The patent positions the drive gear system radially adjacent to the compressor rather than axially between components. This radial placement allows the gear system to occupy space in the radial dimension rather than increasing the axial core flowpath diameter, thereby resolving the contradiction between fan drive power transmission and core flowpath size.
2Adaptability or versatility
If variable pitch fan blades or actuation mechanisms are added, then flow control capability is improved, but the hub diameter increases
Solution Approach 1:
The patent segments the bearing support function by providing separate bearing arrangements at multiple locations along the fan shaft. This segmentation allows the hub to remain compact while distributing the support loads, enabling space for actuation mechanisms without increasing hub diameter.
3Reliability
If multiple bearings are used to support the fan shaft, then radial and thrust load support is improved, but the device complexity increases
Solution Approach 1:
The patent designs bearing arrangements that serve multiple functions: supporting radial loads, supporting thrust loads, and providing precise axial positioning of the fan shaft. By making each bearing arrangement multi-functional, the overall system achieves high reliability without proportionally increasing complexity.
4Loss of energy
If the core flowpath radius is minimized for aerodynamic efficiency, then engine efficiency is improved, but the space for bearing arrangements is reduced
Solution Approach 1:
The patent introduces intermediate bearing arrangements positioned radially outward from the core flowpath but axially aligned with it. These intermediate bearings act as mediators, providing necessary support functions without intruding into the optimized core flowpath, thus maintaining aerodynamic efficiency while ensuring adequate bearing space.
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 configuration enhances the engine's efficiency by optimizing the flowpath geometry and bearing support, allowing for better management of loads and improved stability, thus enhancing the performance and structural integrity of the turbofan engine.
Implementation Method 1
Ball bearings typically react thrust loads bidirectionally. However, if the inner race is configured to engage just one longitudinal side of the balls while the outer race engages the other longitudinal side, the ball bearing will react thrust unidirectionally.
Implementation Method 2
Examples of such bearings are rolling element bearings such as ball bearings and roller bearings.
Implementation Method 3
Tapered roller bearings typically react thrust unidirectionally.
Data Source
Figure 1
Figure 1A
Figure 2
AI summary
A three-spool turbofan engine (20) has a variable fan nozzle (35). The fan blades have a peak tip radius RT and an inboard leading edge radius RH at an inboard boundary of the flowpath. A ratio of RH to RT is less than about 0.40.