Gas Turbine Tip Fan Differential Gear Speed Control
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Solution Overview
Problem
Gas turbine engines face challenges in accommodating both high-speed and long on-station time requirements, as existing designs often prioritize one over the other, and struggle with efficient thermal management and operational flexibility.
Innovation Solution
A multi-stage fan system with a differential gear assembly that allows for varying rotational speeds of fan stages, enabling adaptation to different operational conditions through blade pitch and camber adjustments, and utilizing a tip fan to influence airflow and thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single-speed fan design is used, then the engine structure is simple, but it cannot accommodate both high-speed and long on-station time requirements
Solution Approach 1:
The fan system is segmented into multiple independent fan stages (e.g., core fan and bypass fan) that can rotate at different speeds. Each fan stage has its own drive system, allowing independent speed control to accommodate different operational requirements such as high-speed flight and long on-station time conditions.
Solution Approach 2:
The fan system transitions from a static single-speed design to a dynamic multi-speed design. Variable speed drives and controllable pitch mechanisms allow the fan blades to adjust their rotational speed and angle of attack in real-time, enabling the engine to adapt to varying operational conditions efficiently.
2Temperature
If fan stages rotate at the same speed, then the drive system is simple, but thermal management and airflow optimization are limited
Solution Approach 1:
The fan assembly is divided into multiple independently controllable fan stages, each capable of rotating at different speeds. This segmentation allows optimized airflow paths for thermal management, with each stage contributing differently to cooling and heat dissipation based on operational conditions.
Solution Approach 2:
The system changes operational parameters by allowing different rotational speeds for different fan stages. This parameter variation enables optimized thermal management across different operating conditions, improving heat transfer efficiency and temperature control without requiring a completely redesigned thermal system.
3Productivity
If all fan blades have the same pitch and camber, then manufacturing is simpler, but performance across different operating conditions deteriorates
Solution Approach 1:
Different fan blade sections have different pitch and camber characteristics optimized for their specific functional requirements. For example, inner fan blades may have different geometries compared to outer blades, allowing each section to perform its specific function optimally while maintaining overall system efficiency across various operating conditions.
Solution Approach 2:
The fan blades incorporate variable pitch and camber mechanisms that allow dynamic adjustment of blade geometry during operation. This dynamic capability enables the blades to optimize their aerodynamic performance for different flight conditions, transitioning from fixed geometry to adaptive geometry for improved operational efficiency.
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
Enables efficient operation across a range of speeds and loiter times by optimizing fan stage rotational speeds and airflow, improving thermal management and reducing spillage drag, while maintaining core supercharging and thermodynamic efficiency.
Implementation Method 1
an epicyclic differential gear assembly operative to receive a torque input and differentially apply the torque input to the first set of blades and the second set of blades
Implementation Method 2
a first rotatable set of blades operative to interact with gas moving along the first gas flow path, the second gas flow path and the third gas flow path
Data Source
AI summary
Gas turbine engine systems involving tip fans are provided. In this regard, a representative gas turbine engine system includes: a multi-stage fan having a first rotatable set of blades and a second counter-rotatable set of blades, the first rotatable set of blades defining an inner fan and a tip fan; and an epicyclic differential gear assembly operative to receive a torque input and differentially apply the torque input to the first set of blades and the second set of blades.