Aircraft Pylon Shear Layer Mixing for Jet Noise Reduction
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Solution Overview
Problem
Aircraft gas turbine engines generate significant noise during takeoff and landing due to the downstream mixing of bypass and core flows, which is exacerbated by the interaction between the jet shear layer and the wing and flap surfaces, leading to acoustic pressure fluctuations and radiated noise.
Innovation Solution
A pylon design that spans the bypass duct between the fan nacelle and the core fairing, with laterally-spaced side faces that extend rearwardly and feature convex or concave regions to control airflow, merge bottom edges to enhance mixing, and include channels or ridges to alter turbulence levels and flow characteristics, thereby reducing jet noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the pylon spans the bypass duct to join the engine core to the aircraft, then the engine is securely attached to the wing, but the pylon interrupts the annular continuity of the bypass duct and affects the flow field, leading to increased noise generation
Solution Approach 1:
The pylon is divided into multiple functional sections: a span section that divides the bypass duct into upper and lower passages, and a rearward extension section that projects behind the core engine exhaust nozzle. This segmentation allows the pylon to simultaneously provide structural attachment and control flow separation, reducing noise while maintaining attachment strength.
Solution Approach 2:
The pylon acts as an intermediary structure between the engine and the aircraft wing, and also as a flow control element within the bypass duct. By positioning the span section within the bypass duct, it mediates the flow field to reduce mixing noise between core and bypass flows, while still providing the necessary mechanical attachment function.
2Productivity
If the pylon extends rearwardly of the core engine exhaust nozzle, then the pylon can control the flow field of exhaust gas and improve mixing, but the pylon may interfere with the exhaust flow and increase drag
Solution Approach 1:
The rearward extension of the pylon is designed to be positioned dynamically relative to the exhaust flow, projecting behind the core engine exhaust nozzle to control the mixing zone. This dynamic positioning allows the pylon to enhance mixing efficiency while minimizing interference with the primary exhaust flow, thereby reducing drag penalties.
3Productivity
If the bottom edges of the side faces are merged to form a single bottom edge, then the flow symmetry and mixing are improved, but the manufacturing complexity increases
Solution Approach 1:
While the overall design seeks symmetry for flow balance, the merging of bottom edges creates a controlled asymmetric feature that improves flow symmetry downstream. This deliberate asymmetric design element enhances mixing efficiency by creating more uniform flow patterns, while the symmetry in the upper portions of the pylon maintains ease of manufacturing through standardized production processes.
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 pylon design effectively reduces jet noise by decelerating or accelerating airflow, merging shear layers, and improving mixing of core and bypass flows, leading to a weakening of the shear layer strength and altered turbulence levels, resulting in decreased noise generation.
Implementation Method 1
enhancing mixing of the core and bypass flows and redistribution of the air flow in the vicinity of an attachment pylon for the engine
Implementation Method 2
the proximity of the jet shear layer generated by the air leaving the engine to the wing and flap of the aircraft leads to acoustic pressure fluctuations
Data Source
AI summary
A pylon for attachment of a gas turbine engine to a wing of an aircraft has a trailing edge which is rearward of the trailing edge of the core fairing and the trailing edge of the fan nacelle. The pylon has two laterally-spaced side faces which extend in the rearward direction of the engine to end at the trailing edge of the pylon. Each side face has a bottom edge which extends in a rearward direction of the engine from the core fairing to the bottom end of the trailing edge of the pylon. The bottom edges merge such that the bottom edges form a single bottom edge. The pylon is intended to exert control on the bypass flow of a gas turbine engine. Other pylons are also provided which can also exert such control.