Gas Turbine Gear Reduction for Fan Speed Optimization
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Solution Overview
Problem
Traditional gas turbine engines face efficiency decreases due to high fan blade tip speeds resulting from larger fan diameters, which increase centrifugal stress and reduce performance, as the low pressure turbine section is directly coupled with the fan and compressor, limiting design flexibility.
Innovation Solution
The implementation of a gear reduction system between the low pressure spool and the fan allows for independent speed optimization of the fan and turbine sections, with a planetary or star-type gear reduction enabling the fan to rotate at a lower speed than the low pressure turbine section, thereby improving efficiency and reducing centrifugal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the fan diameter is increased to improve fuel consumption, then fuel efficiency is improved, but fan blade tip speed increases causing compressibility effects and efficiency decrease
Solution Approach 1:
A gear reduction system is introduced as an intermediary mechanism between the low pressure turbine and the fan. This gear system allows the turbine to rotate at high speed while the fan rotates at a lower, optimized speed, decoupling the direct speed relationship and enabling independent optimization of both components
Solution Approach 2:
The invention changes the speed parameter relationship between the turbine and fan from direct coupling to reduced coupling. By implementing a gear reduction with ratio greater than 2.3:1, the fan speed is reduced to optimal levels while maintaining the turbine's high-speed operation, thereby eliminating compressibility effects at the fan blades
2Use of energy by moving object
If the fan diameter is increased to improve fuel consumption, then fuel efficiency is improved, but centrifugal stress on fan blades increases
Solution Approach 1:
The gear reduction system acts as a mediator that allows the use of larger diameter fans without proportionally increasing the rotational speed. By reducing the fan speed through gear reduction, the centrifugal stress (which is proportional to the square of rotational speed) is significantly reduced, enabling larger fan diameters to be used efficiently
Solution Approach 2:
The invention changes the operational parameters by decoupling fan diameter from fan speed through gear reduction. This allows the fan diameter to be increased for better fuel consumption while the speed is reduced through the gear system, thereby controlling centrifugal stress within acceptable limits
3Device complexity
If the low pressure turbine section is directly coupled with the fan and compressor, then the structure is simple, but design flexibility is limited and efficiency is reduced
Solution Approach 1:
The gear reduction system serves as an intermediary that adds design flexibility without excessive complexity. It enables independent speed optimization of the fan and turbine sections, allowing the fan to rotate at optimal speed while the turbine operates at high speed for efficient energy extraction
Solution Approach 2:
The invention segments the speed control of different components by introducing a gear reduction system between the turbine and fan. This segmentation allows each component (turbine and fan) to operate at its optimal speed independently, improving overall efficiency while maintaining manageable structural complexity
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 overall engine efficiency, allows for a more optimal fan speed, and results in a smaller, more efficient turbine section, while improving the low pressure compressor section's performance, achieving higher propulsive efficiency and reducing the engine's size.
Implementation Method 1
A gear reduction is included between the fan and a low spool driven by the first turbine section such that the fan rotates at a lower speed than the first turbine section
Implementation Method 2
Products of this combustion pass downstream over a high pressure turbine section, and then a low pressure turbine section
Implementation Method 3
The air is compressed in the low pressure compressor section, and passed into a high pressure compressor section
Data Source
AI summary
A gas turbine engine includes a very high speed low pressure turbine such that a quantity defined by the exit area of the low pressure turbine multiplied by the square of the low pressure turbine rotational speed compared to the same parameters for the high pressure turbine is at a ratio between about 0.5 and about 1.5.