Turbofan Rub Strip Torque Control for Blade Out Loads
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Solution Overview
Problem
Turbofan engines with speed reduction devices face challenges in managing load imbalances during fan blade out events, leading to high structural loads and potential damage, as existing technologies do not effectively control the deceleration rate and torque distribution across the engine components.
Innovation Solution
The implementation of a turbofan engine design featuring a geared architecture with rub strips that generate counteracting torques, allowing for controlled deceleration rates and increased rub torque resistance during fan blade out events, thereby reducing torque imbalances and structural loads on the engine components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is quickly shut down after fan blade out detection, then the response time is reduced and damage progression is minimized, but high loads are exerted on engine parts due to rapid deceleration
Solution Approach 1:
The rub strip is pre-positioned to contact the fan blade tip when imbalance occurs, automatically generating a counteracting torque that opposes the unbalanced input torque before the shutdown sequence completes. This preliminary counter-action reduces the net load on engine parts during the critical deceleration phase.
Solution Approach 2:
The friction between the rub strip and fan blade tip, which might be considered a harmful contact, is intentionally designed to generate beneficial counteracting torque. The rub torque converts the harmful unbalanced rotational energy into a controlled braking force that protects other engine components from excessive loads.
2Productivity
If a speed reduction device is added to allow different rotation speeds between turbine and fan, then propulsive efficiency is improved, but the system becomes more complex and behaves differently during fan blade out events
Solution Approach 1:
The rub strip acts as an intermediary element between the fan blade tip and the engine structure. During normal operation, it remains inactive. During fan blade out events, it mediates the energy transfer by providing controlled friction contact, simplifying the protection mechanism without requiring complex active control systems in the geared architecture.
3Force
If the deceleration rate is reduced to minimize loads, then the stress on engine parts is decreased, but the time required to shut down the engine increases
Solution Approach 1:
The rub strip provides a dynamic braking mechanism that adapts to the actual imbalance conditions. The friction force is naturally modulated by the contact pressure and relative motion between the rub strip and fan blade tip, allowing the deceleration rate to be optimized in real-time rather than following a fixed schedule. This dynamic response reduces stress while maintaining acceptable shutdown timing.
4Reliability
If a frangible bearing blocking system is used to stop the main engine shaft, then the shutdown function is provided, but the system requires additional blocking mechanisms that increase complexity
Solution Approach 1:
The rub strip extracts the torque limiting function from the main shaft blocking system. By providing friction-based torque opposition at the fan blade tip level, it removes the need for complex frangible bearing blocking mechanisms on the main engine shaft, simplifying the overall shutdown architecture while maintaining the essential function of protecting against excessive loads during fan blade out events.
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 design effectively reduces the magnitude of forces on engine structures during unbalanced conditions by adjusting the deceleration rate and torque distribution, protecting the geared architecture and supporting structures from excessive loads, and enabling a reduction in structural requirements and size.
Implementation Method 1
the rub strip is configured to define a desired rate of deceleration of the rotating components... fan blades and at least one of the compressor blades and turbine blades are in contact with corresponding rub strips and generate rub torques
Implementation Method 2
a flex support configured to generate a counteracting torque to the input torque and the fan torque... the flex support generates a grounding torque opposing the input torque
Data Source
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AI summary
A turbofan engine (20) including a fan section (42) including a plurality of fan blades (42) rotatable about an axis (X), a compressor (44) including a plurality of compressor blades (44a, 44b, 44c), a turbine (46) including a plurality of turbine blades (46a, 46b, 46c) and a geared architecture (48) driven by the turbine (46) for driving the fan section (42) at a speed and direction different than the turbine (46) is disclosed. A rub strip (64, 66, 68) proximate at least one of the compressor blades (44a, 44b, 44c), the turbine blades (46a, 46b, 46c) and the fan blades (42) slows rotation when engaged. The rub strip (64, 66, 68) generates a torque opposing rotation when in an engaged condition that is between 2 and 6 times a torque encountered in a non-engaged condition.