Multi-Spool Fan Architecture for Variable Bypass Ratio Control
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Solution Overview
Problem
Variable cycle gas turbine engines face challenges in efficiently varying the bypass ratio between maximum afterburning and cruise conditions due to the complexity of their three-stream architecture, requiring a sophisticated fan design to manage multiple air streams within a limited space.
Innovation Solution
A two-spool turbofan engine design where a high spool and a low spool drive the fan stages, with a bypass duct and control valve arrangement to selectively direct airflow between different flowpaths, allowing for efficient airflow control and heat exchange to optimize thrust and fuel efficiency across various flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a two-stage fan directly feeds all three streams in a three-stream engine architecture, then the bypass ratio can be varied between maximum afterburning and cruise conditions, but the fan design becomes relatively complex and the intermediate case design becomes challenging due to limited area
Solution Approach 1:
The fan is divided into two separate stages: a first fan stage driven by the low spool and a second fan stage driven by the high spool. This segmentation allows each stage to be optimized independently for specific flow paths, reducing overall design complexity while maintaining the capability to vary bypass ratio across different operating conditions.
2Adaptability or versatility
If a two-stage fan directly feeds all three streams, then all air streams can be managed through a single fan architecture, but the available area becomes insufficient to execute three streams in the same required package
Solution Approach 1:
The patent utilizes the radial dimension by positioning the first and second fan stages at different radial locations, with the first fan stage feeding the core stream and second stream, while the second fan stage feeds the auxiliary stream. This dimensional arrangement allows all three streams to be accommodated within the same package area without spatial interference.
3Productivity
If a multi-spool driven fan design is implemented, then fan pressure ratios can be increased and propulsion efficiency improved, but the turbomachinery design becomes more complex
Solution Approach 1:
The first fan stage serves multiple functions by feeding both the core stream and second stream, while the second fan stage feeds the auxiliary stream. This multi-functional arrangement allows the system to achieve high fan pressure ratios and improved propulsion efficiency without proportionally increasing complexity, as each fan stage is optimized for its specific roles.
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 enhances propulsion efficiency, reduces fuel consumption, and allows for a more balanced and compact turbomachinery, achieving higher fan pressure ratios and improved performance across a range of flight conditions compared to traditional engines.
Implementation Method 1
a low spool constructed and arranged to rotate about the engine axis; a fan leading stage connected for rotation to the low spool; and a fan aft stage connected for rotation to the high spool
Data Source
AI summary
A gas turbine engine includes low and high spools constructed and arranged to rotate about an engine axis. The low spool drives at least one leading stage of a fan section and the high spool drives an aft stage of the fan section. The aft stage may generally include a bypass duct for controllably flowing a bypass stream directly from the leading stage and controllably and/or selectively into an auxiliary flowpath and/or into a second flowpath both located radially outward from a core flowpath.