Variable Area Fan Nozzle Sealing and Flow Control
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Solution Overview
Problem
Turbofan engines face challenges in altering their geometries effectively across different flight regimes such as take-off, cruise, and landing, due to varying atmospheric conditions, which existing variable area fan nozzle (VAFN) designs struggle to accommodate efficiently.
Innovation Solution
A turbofan engine nacelle with a VAFN assembly where the front edge is continuously supported within a circumferential slot in the nacelle wall, allowing for translation and exposure of grid-like cascade ports to adjust airflow exit area, with vanes directing airflow aft, and actuator-controlled movement to optimize airflow for different flight altitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the VAFN assembly is moved axially to adjust the exit passage area, then the airflow exit area is changed, but the sealing between the VAFN assembly and nacelle wall becomes compromised
Solution Approach 1:
A seal member is introduced as an intermediary element between the VAFN assembly and the nacelle wall. The seal member includes a seal edge that contacts the nacelle wall and a front surface that contacts the VAFN assembly, maintaining the seal during axial movement through the circumferential slot.
Solution Approach 2:
The seal member is positioned at the front edge of the VAFN assembly, separating the sealing function from the moving structure. This allows the VAFN assembly to move independently while the seal member maintains continuous contact with the nacelle wall through the circumferential slot.
2Productivity
If the exit passage area is increased for takeoff and landing, then the airflow capacity is improved, but the engine geometry becomes less optimized for cruise operation
Solution Approach 1:
The VAFN assembly is designed to be dynamically adjustable along the axial direction, allowing the exit passage area to be changed based on flight conditions. The assembly can be positioned at different locations within the circumferential slot to optimize performance for takeoff, landing, or cruise operations.
Solution Approach 2:
The geometric parameter of the exit passage area is changed by adjusting the axial position of the VAFN assembly. This allows the same engine to be optimized for different flight regimes by modifying the effective exit area through controlled movement of the assembly.
3Adaptability or versatility
If the VAFN assembly is moved forward or aft to adjust geometry, then the engine performance for different flight regimes is improved, but the complexity of the adjustment mechanism increases
Solution Approach 1:
The seal member serves dual functions: it maintains the seal between the VAFN assembly and nacelle wall while also guiding the axial movement of the assembly through the circumferential slot. This self-guiding mechanism reduces the need for additional complex positioning systems.
Solution Approach 2:
The circumferential slot serves multiple purposes: it guides the axial movement of the VAFN assembly, accommodates the seal member, and defines the travel limits of the assembly. This multi-functional design reduces the number of separate components needed for the adjustment mechanism.
Data Source
AI summary
An aircraft turbofan engine variable area fan nozzle (VAFN) is disclosed that has a forward end that is continuously supported within a circumferential recess in the wall of the nacelle in front of it. During operation, the VAFN translates back and forth but always has its front end within the recess. Relatively simple seals help seal the recess against the VAFN. An array of openings with aft facing vanes, termed an aft cascade, is built into the VAFN. The openings are hidden within the recess when the VAFN is in the forward-most positions, and they are exposed to allow air to flow from the bypass duct through the cascade when the VAFN is in aft positions. The aft cascades can have different airflow directions based on their locations around the engine.