Geared Gas Turbine Engine High Bypass Ratio Design
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Solution Overview
Problem
Turbofan gas turbine engines face challenges in achieving high propulsive efficiency with a larger fan diameter while maintaining a compact engine core size for aircraft integration, as increased fan diameter conflicts with low-pressure turbine requirements and leads to integration difficulties under an aircraft wing.
Innovation Solution
Incorporating a gearbox with a gear ratio of 3.4 or higher between the fan and the core shaft, allowing the fan to operate at reduced rotational speed, thereby maintaining high efficiency and reducing the engine core size, while keeping the low-pressure turbine rotational speed high, thus achieving a jet velocity ratio between 0.75 and 0.82 to maintain high bypass ratio and propulsive efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the fan diameter is increased to achieve higher thrust and efficiency, then the propulsive efficiency is improved, but the low-pressure turbine size must increase making aircraft integration difficult
Solution Approach 1:
A gearbox is introduced as an intermediary component between the fan and the low-pressure turbine. The gearbox enables the fan to rotate at a lower speed while the low-pressure turbine rotates at a higher speed, decoupling the speed requirements of these two components. This allows the fan diameter to be increased for higher thrust without proportionally increasing the engine core size, thereby resolving the contradiction between productivity improvement and volume increase.
2Use of energy by moving object
If the bypass ratio is increased to achieve high propulsive efficiency, then the propulsive efficiency is improved, but the engine core size must increase making aircraft integration more difficult
Solution Approach 1:
The gearbox acts as a mediator that allows the system to achieve high bypass ratio and high propulsive efficiency without proportionally increasing the engine core size. By enabling the fan to operate at optimal lower speeds while maintaining high low-pressure turbine speeds, the gearbox facilitates higher bypass ratios without the penalty of enlarged engine core dimensions, thus resolving the contradiction between energy efficiency improvement and volume increase.
3Productivity
If the gear ratio is increased to maintain high fan efficiency, then the fan operates at lower speed, but the gearbox losses and wear increase
Solution Approach 1:
The patent specifies an optimal gear ratio range (around 3.4 or higher, but preferably around 5.0 or 4.5 or less) to balance fan efficiency with gearbox performance. By optimizing this parameter, the system achieves sufficient fan speed reduction for high efficiency while limiting the gear ratio to acceptable levels that minimize gearbox losses and wear, thus resolving the contradiction between productivity improvement and energy loss.
Data Source
AI summary
The present disclosure relates to a geared gas turbine engine for an aircraft. Example embodiments include a gas turbine engine for an aircraft including: an engine core having a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan having a plurality of fan blades; and a gearbox that receives an input from the core shaft to drive the fan at a lower rotational speed than the core shaft, the gearbox having a gear ratio of around 3.4 or higher, wherein the gas turbine engine is configured such that a jet velocity ratio between a first jet velocity exiting from a bypass duct of the engine and a second jet velocity exiting from an exhaust nozzle of the engine core is within a range from around 0.75 to around 0.82.