Geared Turbofan Architecture for Thrust Density
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Solution Overview
Problem
Current gas turbine engines face limitations in achieving optimal thermal, transfer, and propulsive efficiencies, despite advancements in geared architectures.
Innovation Solution
The design incorporates a gearbox-driven speed change system with a fan drive turbine and a second turbine, where the fan and fan drive turbine rotate in one direction, and the second turbine rotates in the opposite direction, along with a bypass ratio greater than 6.0, to enhance thrust density and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a geared architecture is used to improve propulsive efficiency, then the fan can rotate at optimal speed, but the device complexity increases due to additional speed change systems
Solution Approach 1:
The patent employs an epicyclical gear assembly where planet gears are nested around a sun gear, with the sun gear connected to the fan drive turbine and the planet gears meshing with both the sun gear and a ring gear. This nested configuration allows multiple gear stages to be compactly arranged, achieving significant speed reduction (fan rotating at 1/3 to 1/5 of turbine speed) while minimizing the space required for the speed change system.
Solution Approach 2:
The epicyclical gear assembly serves multiple functions simultaneously: it provides speed reduction, supports bearing loads through the ring gear connection to the engine case, and enables compact packaging of the turbine and fan sections. The ring gear acts both as a gear element and as a structural support component, reducing the need for separate bearing structures.
2Power
If the number of turbine stages is increased to improve power transfer, then the thrust density increases, but the volume of the turbine section increases
Solution Approach 1:
The patent optimizes the local quality of the turbine section by carefully selecting the number of stages (2-6 stages) and configuring the blade geometry to achieve high thrust density (greater than 1.5 lbf/in³ and less than or equal to 5.5 lbf/in³ at Sea Level Takeoff Thrust). This allows sufficient power extraction without excessive volume increase.
Solution Approach 2:
The epicyclical gear assembly enables the turbine section to be more compact by allowing the fan to be positioned closer to the turbine. The gear reduction mechanism effectively changes the spatial relationship between the power source (turbine) and the load (fan), enabling a more compact overall engine layout while maintaining the required power transfer.
3Volume of moving object
If the ratio between fan blades and turbine stages is optimized to increase thrust density, then the engine becomes more compact, but the manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the ratio between the number of fan blades and turbine stages to fall within a specific range (greater than 2.5), which balances thrust density achievement with manufacturing feasibility. This parameter optimization ensures that the engine achieves compact dimensions while maintaining reasonable manufacturing precision requirements for the gear assembly and turbine components.
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 increases thrust density, reduces engine weight, and improves fuel efficiency by optimizing the number of turbine stages and fan blades, leading to higher power transfer efficiency and compact engine design.
Implementation Method 1
The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section
Implementation Method 2
A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section
Data Source
AI summary
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section so as to increase the overall propulsive efficiency of the engine. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a speed different than the turbine section such that both the turbine section and the fan section can rotate at closer to optimal speeds providing increased performance attributes and performance by desirable combinations of the disclosed features of the various components of the described and disclosed gas turbine engine.