Variable Fan Nozzle Geometry for Gas Turbine Drag Reduction
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Solution Overview
Problem
Conventional gas turbine engines face inefficiencies in thrust production and drag during engine-out conditions due to insufficient fan bypass flow area, leading to flow spillage and increased drag, particularly at cruise conditions.
Innovation Solution
A variable geometry fan exit guide vane system that allows simultaneous rotation or pivoting of multiple fan exit guide vanes within an intermediate engine case structure, controlled by a gear system and actuator system to adjust the fan nozzle exit area, enabling optimal bypass flow management across different flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fan nacelle diameter is increased to minimize drag during engine-out conditions, then flow spillage and drag are reduced during engine-out conditions, but the fan nacelle diameter becomes larger than necessary during normal cruise conditions resulting in suboptimal drag performance
Solution Approach 1:
The patent applies a variable geometry fan exit guide vane system that dynamically adjusts the fan bypass flow path area based on operating conditions. During engine-out conditions, the system increases the bypass flow area to prevent flow spillage and reduce drag, while during normal cruise conditions, it reduces the bypass flow area to optimize drag performance. This dynamic adjustment resolves the contradiction between maintaining optimal performance in both engine-out and cruise conditions.
2Reliability
If the fan bypass flow path area is increased to prevent flow spillage during engine-out conditions, then thrust is maintained during engine-out conditions, but the fan nacelle diameter must be larger than necessary for cruise conditions
Solution Approach 1:
The variable geometry fan exit guide vane system dynamically adjusts the bypass flow area to match operating conditions. During engine-out conditions, the system expands the bypass flow area to maintain thrust by preventing flow spillage. During normal cruise, the system contracts the bypass flow area to allow for a smaller fan nacelle diameter. This dynamic adjustment eliminates the need to design for the maximum required area, resolving the contradiction between maintaining thrust during engine-out conditions and minimizing fan nacelle diameter for cruise efficiency.
3Device complexity
If conventional fixed geometry fan systems are used, then the design is simpler and more reliable, but the engine cannot optimize performance across different flight conditions resulting in increased drag and reduced fuel efficiency
Solution Approach 1:
The patent implements a variable geometry fan exit guide vane system that adjusts the bypass flow area based on flight conditions. The system includes multiple fan exit guide vanes that can be simultaneously rotated to change the fan bypass flow path area, allowing optimization of engine performance during different flight regimes including take-off, landing, and cruise conditions. This dynamic adjustment capability improves fuel efficiency by reducing drag during cruise while maintaining the ability to handle engine-out conditions, resolving the contradiction between system simplicity and fuel efficiency.
Data Source
Figure 1A
Figure 1B
Figure 2A~2C
AI summary
A turbofan engine (10) includes a fan variable area nozzle (42) axially movable relative to the fan nacelle (34) to vary a fan nozzle exit area (44) and adjust a pressure ratio of the fan bypass airflow (B) during engine operation.