Offset Exhaust Duct Straight Section Flow Separation
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Solution Overview
Problem
Gas turbine engine exhaust systems face increased noise due to aerodynamic flow separation when the exhaust duct is offset from the axial centreline of the aircraft tail cone, as turns in the duct upstream of the exit cause higher exhaust gas velocity and noise, which existing silencers cannot effectively mitigate.
Innovation Solution
An exhaust duct system for gas turbine engines with an offset exhaust exit, featuring a straight section of duct that extends at least one diameter, minimizing aerodynamic flow separation and noise by eliminating bends upstream of the exit, and optionally including an exhaust silencer to further reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the exhaust duct is offset from the axial centreline to shield noise from critical locations, then noise shielding is improved, but aerodynamic flow separation occurs causing increased exhaust noise
Solution Approach 1:
The exhaust duct is segmented into multiple sections: a first section with a turn to achieve offset positioning, and a second section that is substantially straight to minimize flow separation. This segmentation allows the duct to fulfill both the noise shielding requirement (through offset positioning) and the noise reduction requirement (through straight section minimizing flow separation).
Solution Approach 2:
Different sections of the exhaust duct have different geometric qualities optimized for different functions. The first section has a turn geometry optimized for noise shielding, while the second section has a straight geometry optimized for minimizing flow separation and exhaust noise. This local differentiation resolves the contradiction between noise shielding and noise generation.
2Object-affected harmful factors
If a turn is included in the exhaust duct to accommodate side-mounted exhaust exit, then noise shielding is improved, but flow separation increases causing higher exhaust gas velocity and noise
Solution Approach 1:
The exhaust duct is divided into a first section containing the turn and a second section that is substantially straight. By isolating the turn to only the first section and ensuring the second section is straight, the design minimizes flow separation and prevents excessive exhaust gas velocity in the majority of the duct length, thus reducing noise while maintaining noise shielding capability.
Solution Approach 2:
The turn is positioned in the first section upstream of the second straight section. This preliminary positioning allows the exhaust flow to complete its directional change before entering the long straight section, enabling the flow to stabilize and reducing flow separation effects in the majority of the duct length, thereby controlling exhaust gas velocity and noise.
3Object-affected harmful factors
If the exhaust exit is offset from the centreline, then noise shielding from critical locations is improved, but the exhaust duct requires turns that cause aerodynamic flow separation
Solution Approach 1:
The exhaust duct is segmented into a first section with a turn for offset positioning and a second section that is substantially straight. This segmentation stabilizes the flow composition in the second section by eliminating continuous turns, thereby maintaining flow stability while still achieving noise shielding through the offset exit position established in the first section.
Solution Approach 2:
The duct geometry varies locally: the first section has turn geometry to achieve offset positioning for noise shielding, while the second section has straight geometry to stabilize the flow. This local quality differentiation resolves the contradiction between achieving offset positioning and maintaining flow stability.
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 effectively reduces exhaust noise by eliminating flow separation and increasing duct length to manage gas velocity, allowing the silencer to operate effectively in reducing noise levels when the exhaust exit is offset from the centreline, thus meeting stringent noise limits.
Implementation Method 1
a straight section of the exhaust duct extending from the exhaust exit for a length that corresponds to at least one diameter of the exhaust duct... the turn in the exhaust duct upstream of the exhaust exit causes aerodynamic flow separation of the exhaust gases, thereby increasing exhaust gas velocity and flow noise
Data Source
AI summary
An exhaust duct system for a gas turbine engine that mounts within a tail cone of an aircraft, comprises an exhaust exit that exits one side of the tail cone offset from the axial centerline of the tail cone and an exhaust duct that couples the engine to the offset exhaust exit, with a straight section of the exhaust duct extending from the exhaust exit for a length that corresponds to at least one diameter of the exhaust duct.