Variable-Pitch Shrouded Fan for Low Pressure Ratio
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Solution Overview
Problem
Existing gas turbine engines face inefficiencies due to large fan assemblies, which increase weight and drag, and are susceptible to flutter and inlet flow distortion, especially in high bypass ratio turbofans, where large fan blades require larger turbine sizes and are prone to unsteady loading.
Innovation Solution
A low fan pressure ratio shrouded fan assembly with variable-pitch fan blades and a shroud mechanism that allows each blade to rotate independently, reducing the need for a traditional thrust reverse mechanism and providing additional support to mitigate flutter and inlet distortion, while enabling a more robust mechanical design and reducing nacelle size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a large diameter fan assembly is used to increase bypass ratio and efficiency, then engine efficiency is improved, but weight and drag penalties increase
Solution Approach 1:
The fan blades are designed with variable pitch capability, allowing the pitch angle to be adjusted dynamically. This enables the fan assembly to optimize its performance across different operating conditions, maintaining high efficiency without requiring excessive blade size and weight. The shroud further enhances this by providing aerodynamic benefits that improve efficiency without adding proportional weight.
Solution Approach 2:
The shroud serves multiple functions: it improves aerodynamic efficiency, reduces the need for traditional thrust reverse mechanisms, and provides structural support. This multi-functionality allows the system to achieve high efficiency without proportionally increasing weight, as the same component addresses multiple performance requirements.
2Use of energy by moving object
If large fan assembly size is increased to achieve higher bypass ratio, then engine efficiency is improved, but drag penalties increase
Solution Approach 1:
Variable pitch control allows the fan blades to optimize their angle of attack for different flight conditions, minimizing drag at various speeds and altitudes. This dynamic adjustment prevents the drag penalties that would otherwise require larger, heavier blades to maintain efficiency.
Solution Approach 2:
By changing the pitch parameter of the fan blades, the system can optimize the balance between thrust generation and drag creation. This allows high bypass ratio operation with reduced drag compared to fixed-pitch designs of equivalent size.
3Quantity of substance
If long fan blades are used on large fans, then bypass ratio is improved, but flutter and inlet flow distortion increase
Solution Approach 1:
Variable pitch capability allows the blades to adjust their angle, which can help control aerodynamic loads and reduce flutter tendencies. The shroud provides additional aerodynamic stability and support, mitigating the flutter and inlet flow distortion issues that typically accompany long blades.
Solution Approach 2:
The shroud acts as an intermediary structure that provides aerodynamic support to the long fan blades. It helps stabilize the blade tips and reduces the harmful aerodynamic interactions that cause flutter and flow distortion, enabling the use of long blades for high bypass ratio without sacrificing reliability.
4Reliability
If variable-pitch fan blades with shroud are implemented, then blade support and flutter mitigation are improved, but device complexity increases
Solution Approach 1:
The shroud provides multiple benefits simultaneously: it supports the blade tips to reduce flutter, improves aerodynamic efficiency, and eliminates the need for separate thrust reverse mechanisms. This multi-functionality offsets the added complexity by consolidating multiple functions into a single component.
Solution Approach 2:
The invention combines the shroud structure with the variable pitch mechanism into an integrated fan assembly. By merging these functions and the elimination of separate thrust reverse mechanisms, the overall system complexity is managed more effectively than if these were separate additions.
Data Source
AI summary
A shrouded fan assembly for use with a gas turbine engine includes a central hub and a plurality of variable-pitch fan blades coupled to and extending radially outward from the central hub. Each variable-pitch fan blade includes a radially outer tip is rotatable about a longitudinal axis extending therethrough. A shroud is coupled to each radially outer tip.