Translating Variable Area Fan Nozzle With Upstream Bypass Deflector
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Solution Overview
Problem
Existing variable area nozzle systems for turbofan aircraft engines are heavy, expensive, and complex, making them inefficient for cost-effective control of engine output under varying flight conditions.
Innovation Solution
A translating variable area fan nozzle assembly that includes a movably disposed nozzle segment with a deflector to prevent bypass flow from exiting through an upstream bypass flow exit, allowing for adjustment of the fan nozzle exit area to optimize engine performance by bleeding excess fan flow, thereby increasing stall margins and avoiding engine malfunction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If prior variable area nozzle systems are used to control fan nozzle exit area, then engine performance can be adjusted under varying flight conditions, but the system becomes heavy, expensive and complex with multiple components and drive mechanisms
Solution Approach 1:
The nozzle system is divided into a stationary forward nozzle section and a translating aft nozzle section. The aft section can move independently relative to the forward section, allowing variable area control through simple translation rather than complex multi-component coordination. This segmentation enables performance adjustment while maintaining structural simplicity.
Solution Approach 2:
The aft nozzle section is designed to translate dynamically relative to the forward nozzle section based on flight conditions. This dynamic positioning allows the nozzle exit area to be adjusted continuously, providing adaptability while using a simple translational mechanism rather than complex rotating or telescoping systems.
2Loss of energy
If a higher bypass ratio is used to improve efficiency and reduce noise, then exhaust velocity decreases and jet noise reduces, but the fan pressure ratio must be increased which can cause fan stall, blade flutter or compressor surge
Solution Approach 1:
The system allows the bypass flow to exceed the capacity of the primary nozzle exit by creating an additional upstream exit path. When the aft nozzle section translates forward, it opens the upstream bypass flow exit, providing an overflow path that prevents excessive pressure buildup and eliminates fan stall conditions while maintaining high bypass ratio benefits.
Solution Approach 2:
The upstream bypass flow exit acts as an intermediary pressure relief path between the fan and the primary nozzle exit. By providing this intermediate escape route, the system prevents pressure accumulation that would cause fan stall, blade flutter, or compressor surge, thereby maintaining reliability in high bypass ratio configurations.
3Productivity
If the fan nozzle exit area is reduced to increase back pressure and improve propulsive efficiency, then engine efficiency increases, but excess fan flow can cause fan stall and engine malfunction
Solution Approach 1:
The system deliberately allows excess fan flow to occur by providing an upstream bypass exit. The aft nozzle section translates forward to open this exit, intentionally creating an overflow path that prevents pressure buildup. This partial action approach maintains propulsive efficiency while eliminating the risk of fan stall by allowing controlled excess flow.
Solution Approach 2:
The system converts the potentially harmful effect of excess fan flow into a beneficial pressure relief mechanism. By providing the upstream bypass flow exit, what would normally be harmful (excess flow causing stall) becomes useful (pressure relief preventing stall), thereby improving both efficiency and reliability.
Data Source
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AI summary
A variable area fan nozzle assembly for a turbofan engine includes a nacelle having an aft edge and a translating nozzle segment having a forward edge and a first end. The nozzle segment is movably disposed behind the aft edge such that an upstream bypass flow exit is defined between the aft edge and the forward edge when the nozzle segment is in a deployed position. A deflector is disposed between the aft edge and the forward edge proximate to the first end. The deflector substantially prevents bypass flow from exiting the upstream bypass flow exit in a region that is proximate to the first end.