Variable-Section Flow Mixer for Supersonic Jet Engine Noise Reduction
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Solution Overview
Problem
Low-bypass turbofan engines for supersonic aircraft face a contradiction between minimizing drag and noise during transonic and supersonic flight, where small-diameter engines reduce drag but increase noise due to higher gas ejection speeds, and conventional variable section flow mixers lengthen the engine, increasing weight and requiring acoustic coatings.
Innovation Solution
A variable-section flow mixer with lobes having an azimuthal component that impart a gyratory motion to external air, enhancing mixing between cold and hot flows, allowing for a shorter engine length and reduced noise while maintaining acoustic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional variable section flow mixer is used to reduce jet noise by introducing external air, then noise level decreases, but the engine length increases significantly
Solution Approach 1:
The lobes are designed with an azimuthal component that imparts a gyratory motion to the external air flow, introducing a rotational dimension to the mixing process. This gyration enhances mixing efficiency within a shorter axial length, allowing the mixer to achieve effective mixing without significantly increasing engine length.
Solution Approach 2:
The lobes are made movable between two positions: a first position where they obstruct the openings and a second position where they release the openings and extend radially to allow external air admission. This parameter change in lobe position enables the system to switch between mixing modes, optimizing noise reduction during take-off while maintaining compact engine length.
2Productivity
If the engine length is increased to promote mixing between external air and gaseous flow, then mixing efficiency improves, but the engine weight increases
Solution Approach 1:
By introducing the azimuthal component that creates gyratory motion, the mixing process utilizes rotational movement rather than relying solely on axial length. This dimensional change allows efficient mixing to occur within a compact axial length, thereby avoiding the weight penalty associated with elongating the engine.
Solution Approach 2:
The lobes are designed to be movable between obstructing and releasing positions, dynamically controlling the admission of external air. This dynamic capability allows the system to optimize mixing efficiency during take-off phases without requiring a permanently elongated engine structure, thus maintaining weight efficiency.
3Loss of energy
If small-diameter turbojet architecture is used to minimize drag during supersonic flight, then drag decreases, but gas ejection speed increases which increases noise
Solution Approach 1:
The movable lobes enable the system to dynamically adjust the gas flow characteristics during take-off by admitting external air and creating gyratory motion. This dynamic mixing process allows the engine to operate with optimized flow patterns that reduce noise during high-speed phases while maintaining the compact diameter necessary for low drag during supersonic flight.
Solution Approach 2:
The system changes the flow parameters by introducing external air through the movable lobes during take-off, creating a mixed flow that reduces gas ejection speed and noise. During supersonic flight, the lobes obstruct the openings, maintaining the original high-speed flow pattern that minimizes drag, thus adapting parameters to match operational requirements.
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 reduces jet noise on take-off and decreases engine weight by promoting efficient mixing within a reduced engine length, compared to conventional mixers, while maintaining acoustic performance.
Implementation Method 1
the lobes have an azimuthal component in the same direction so as to impart a gyratory motion to the external air admitted into the convergence zone
Implementation Method 2
the gyration of the air which is generated by this particular shape of the lobes increases the existing shear effects in the zone of convergence between the cold and hot flows coming from the gas generator
Data Source
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AI summary
The invention relates to a variable area flow mixer for a supersonic aircraft turbofan engine, comprising a nozzle (24) intended to be arranged around a gas generator of the turbofan engine, the nozzle having a plurality of external air intake openings (30) opening into a convergence zone between cold and hot flows from the gas generator and in which lobes (32) movable between two positions are mounted; a first position in which they obstruct the openings (30) of the nozzle (24) and a second position different from the first in which they clear said openings and extend radially in the nozzle (24) so as to allow an external air intake, the lobes (32) having an azimuthal component in the same direction so as to give a gyratory motion to the external air admitted into the convergence zone when the lobes are in the second position.