Geared Turbofan Thrust Bearing Layout for Turbine Over-Speed
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Solution Overview
Problem
Gas turbine engines face challenges in managing over-speed conditions of the low pressure turbine due to decoupling during fan drivetrain failures, particularly when a gear reduction is included between the fan drive turbine and low pressure compressor.
Innovation Solution
Incorporating a thrust bearing to maintain the low speed spool's axial position and employing a tower shaft connected to the low speed spool to provide a counter-load, along with a braking mechanism and fuel shutoff procedure to prevent over-speed conditions during fan drivetrain failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a gear reduction is included between the fan drive turbine and fan section to allow turbine to rotate at higher speed, then turbine speed capability is improved, but turbine over-speed risk worsens in event of fan drivetrain failure
Solution Approach 1:
The low speed spool is divided into two separate components: a low speed shaft section mounting the low pressure turbine and an input shaft section driving the geared architecture. These separate components are fixed to rotate together normally but can decouple during failure conditions, allowing the turbine to be isolated from the fan drivetrain while maintaining independent rotational control
Solution Approach 2:
A thrust bearing is introduced as an intermediary component positioned between the low speed spool and the fan drivetrain. This thrust bearing maintains the low speed spool axially in place and provides over-speed protection by limiting the turbine's rotational speed in event of fan drivetrain failure, acting as a mechanical governor
2Reliability
If thrust bearing is used to maintain low speed spool axial position, then over-speed protection is improved, but device complexity worsens
Solution Approach 1:
The thrust bearing performs multiple functions: it maintains the low speed spool axially in place during normal operation, provides over-speed protection during fan drivetrain failure, and supports the mechanical separation between the low speed shaft section and input shaft section. By consolidating these functions into a single component, the overall device complexity is minimized
3Reliability
If low speed spool is decoupled from fan drivetrain during failure, then over-speed protection is improved, but control complexity worsens
Solution Approach 1:
The control system is configured to detect fan drivetrain failure conditions and initiate corrective actions including fuel shutoff and activation of braking mechanisms. The braking mechanism is directly connected to the low speed spool, providing immediate mechanical counter-action to prevent over-speed conditions before they can develop into dangerous situations
Data Source
Figure 1
Figure 2
AI summary
A gas turbine engine (100) includes a fan shaft (110) rotatable about an axis (A), a fan (112) connected to the fan shaft (110), and an outer housing (114) surrounding the fan (112) to define a bypass passage (B). A compressor section (24) has both a low pressure compressor (106) that is fixed to rotate with the fan shaft (116) and a high pressure compressor (124). A turbine section (28) has a low pressure turbine (104) driving a low speed spool (116) and a high pressure turbine (122) driving the high pressure compressor (124). The low pressure turbine (104) includes rotating blades and a static structure (130) aft of the rotating blades. A fan drivetrain (120) includes a geared architecture (102) connecting the low speed spool (116) to the fan shaft (110) such that the fan (112) and low pressure compressor (106) rotate at a lower speed than the low pressure turbine (104). A thrust bearing (132) is axially aft of the geared architecture (102) and axially forward of the high pressure compressor (122). A tower shaft (140) is rotatably driven by the low speed spool (116).