Compact Muffling Device for Gas Turbine Noise Reduction
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Solution Overview
Problem
Conventional muffling devices for gas turbine engines are large and heavy, requiring extensive thermal shielding due to high-pressure and high-temperature bleed air, which can overwhelm surrounding structures, and fail to meet acoustic limits efficiently, especially in aircraft applications where lightweight materials are used.
Innovation Solution
A compact, lightweight muffling device featuring an inner flow conditioner shaped as a conical frustum with a larger upstream base and smaller downstream base, integrated with an exhaust can, which directs high-pressure bleed air at high velocity into the fan duct, reducing noise and minimizing thermal impact on surrounding structures by distributing heat within the cool fan duct flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large exhaust area and gentle expansion are used to reduce flow velocity below acoustic limits, then noise reduction is improved, but device size and weight increase
Solution Approach 1:
The patent changes the expansion parameter from gentle to abrupt by using a sudden expansion chamber where the cross-sectional area increases sharply. This abrupt expansion creates strong turbulence and mixing that effectively reduces noise without requiring a large overall device size, thus resolving the contradiction between noise reduction and device weight.
Solution Approach 2:
The muffling device is segmented into distinct functional zones: an abrupt expansion chamber for initial noise reduction through turbulence, followed by a series of smaller expansion sections. This segmentation allows noise control to be achieved in a compact configuration rather than requiring a single large gradual expansion, reducing overall device weight.
2Productivity
If high temperature bleed air is exhausted at high velocity, then engine performance is maintained, but thermal impact on surrounding structures increases
Solution Approach 1:
The patent introduces cool bypass air as an intermediary substance that mixes with the hot bleed air in the expansion chamber. This mixing process reduces the temperature of the exhaust stream before it contacts surrounding structures, thereby reducing thermal impact while maintaining the high-velocity exhaust needed for engine performance.
Solution Approach 2:
The patent converts the harmful high temperature into a beneficial mixing process. The temperature difference between hot bleed air and cool bypass air creates strong convection currents and turbulence that enhance mixing and noise reduction, while the resulting temperature reduction protects surrounding structures.
3Object-affected harmful factors
If conventional muffling devices are used to reduce noise, then acoustic limits are met, but extensive thermal shielding is required
Solution Approach 1:
The patent merges the noise reduction function and thermal management function into a single integrated expansion chamber design. The abrupt expansion geometry simultaneously creates turbulence for noise reduction and promotes mixing with cool air for thermal management, eliminating the need for separate thermal shielding components and reducing overall device complexity.
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 achieves significant noise reduction with minimal acoustic impact and reduces the need for thermal shielding, allowing for the use of lightweight materials while maintaining engine performance and safety.
Implementation Method 1
The inner flow conditioner downstream end wall comprises a plurality of generally longitudinally oriented inner flow conditioner downstream end wall holes, and the inner flow conditioner sidewall comprises a plurality of generally laterally oriented inner flow conditioner sidewall holes
Implementation Method 2
directs high-pressure bleed air at high velocity into the fan duct, reducing noise and minimizing thermal impact on surrounding structures by distributing heat within the cool fan duct flow
Data Source
AI summary
Some example muffling devices may include an inner flow conditioner shaped as a generally conical frustrum and a generally cylindrical an exhaust can around the inner flow conditioner. A ratio of a downstream end wall area of the inner flow conditioner to a downstream end annular area between the downstream end wall and the exhaust can may be about 0.12 to about 0.97. A ratio of the downstream end annular area to the downstream end wall area may be proportional, by a factor of about 0.8 to about 1.9, to a ratio of an effective area of the inner flow conditioner sidewall holes to an effective area of the inner flow conditioner downstream end wall holes. A ratio of a dissipation distance between the inner flow conditioner downstream end wall and the exhaust screen to the inner flow conditioner downstream end wall hole diameter may be greater than about 10.