Variable Pitch Fan Cowl Deflection Device for Reverse Thrust
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Solution Overview
Problem
Existing gas turbine engines with variable pitch fans face suboptimal bypass flow conditions in both forward and reverse thrust modes, leading to inefficient thrust generation.
Innovation Solution
A gas turbine engine design incorporating a variable pitch fan with a fan cowl and an airflow deflection device, such as a spoiler, that remains a strictly external mechanism, allowing the physical flow area to remain constant across thrust modes, and is deployed or stowed to optimize airflow and reduce flow separation in the bypass duct.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bypass duct flow area is increased to improve reverse thrust, then reverse thrust capability is improved, but the physical structure of the fan cowl must change between thrust modes
Solution Approach 1:
The fan cowl incorporates movable deflection devices (spoilers) that can change position between forward and reverse thrust modes. These dynamic elements allow the effective flow area to be increased for reverse thrust while maintaining a simple fixed physical structure, resolving the contradiction between improved reverse thrust capability and reduced structural complexity
Solution Approach 2:
The fan cowl is divided into fixed structural sections and movable deflection device sections. The deflection devices can be independently positioned to alter the effective flow area without requiring the entire fan cowl structure to change, enabling simplified construction with improved reverse thrust performance
2Reliability
If the bypass duct flow area is increased to improve airflow quality, then airflow quality is improved, but the physical flow area cannot be changed without modifying the fan cowl structure
Solution Approach 1:
Movable deflection devices allow the effective flow area to be dynamically adjusted for optimal airflow quality in reverse thrust mode, while the physical fan cowl structure remains simple and fixed. This resolves the contradiction by decoupling effective flow area from physical structure
Solution Approach 2:
The deflection devices change the effective flow area parameter without changing the physical dimensions of the fan cowl. By altering the position of these devices, the airflow characteristics are improved while maintaining structural simplicity
3Productivity
If flow separation is reduced to improve thrust efficiency, then thrust efficiency is improved, but additional thrust generation capability is required
Solution Approach 1:
The deflection devices convert what would be harmful flow separation into beneficial flow guidance. By strategically positioning these devices, the airflow that might otherwise separate is redirected to attach to the fan cowl surface, improving thrust efficiency without requiring additional power
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
The solution enhances the quality and quantity of airflow in the bypass duct, improving both forward and reverse thrust capabilities by minimizing flow separation and pressure losses, and reducing the need for additional thrust generation in reverse thrust mode.
Implementation Method 1
The spoiler is configured for being stowed in the forward thrust mode of the engine and for being deployed in the reverse thrust mode of the engine
Data Source
AI summary
A gas turbine engine having a forward thrust mode and a reverse thrust mode is provided. The gas turbine engine includes a variable pitch fan configured for generating forward thrust in the forward thrust mode of the engine and reverse thrust in the reverse thrust mode of the engine. The engine also includes a fan cowl surrounding the variable pitch fan, wherein the fan cowl forms a bypass duct for airflow generated by the fan. The fan cowl includes an aft edge that defines a physical flow area of the bypass duct, and a deflection device configured for deflecting airflow near the aft edge, wherein the deflection device is configured for operation in the reverse thrust mode of the engine. The physical flow area of the bypass duct at the aft edge remains the same in the forward thrust mode of the engine and in the reverse thrust mode of the engine.