Variable-Section Flow Mixer with Counter-Rotating Lobes
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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 cruise, and reducing jet noise during takeoff, where increasing thrust diameter contradicts noise reduction requirements, and existing variable section flow mixers either lengthen the engine or reduce thrust.
Innovation Solution
A variable-section flow mixer with a central annular body, primary and secondary cowls, and an annular nozzle featuring movable lobes with an azimuthal component and opposing grooves on the central body, allowing external air intake during takeoff to mix with gas flows while maintaining thrust by counter-rotating the air flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the fan diameter is increased to raise thrust and reduce jet noise, then the noise level decreases, but the drag increases
Solution Approach 1:
The patent employs movable lobes that can transition between a retracted position (for cruise flight with minimal drag) and an extended position (for takeoff with noise reduction). This dynamic adjustment allows the mixer geometry to adapt to different flight phases, resolving the contradiction between drag minimization and noise reduction.
Solution Approach 2:
The mixer changes its effective geometric parameters (opening area, flow mixing ratio) by extending or retracting the lobes. During takeoff, the lobes extend to increase external air intake and mixing, reducing jet noise. During cruise, the lobes retract to minimize drag, thus resolving the parameter-based contradiction.
2Object-affected harmful factors
If a variable section flow mixer is used to reduce jet noise by mixing external air, then the noise level decreases, but the engine length increases
Solution Approach 1:
Instead of extending the engine axially to achieve mixing, the patent uses lobes that extend radially into the nozzle flow path. This dimensional change from axial to radial extension allows the mixer to function within the existing engine length, reducing jet noise without increasing engine length.
Solution Approach 2:
The lobes are nested within the nozzle structure, allowing them to extend into the flow path when needed and retract when not needed. This nested configuration enables the mixer to be compact while still providing effective noise reduction during takeoff.
3Productivity
If lobes with azimuthal component are used to promote mixing by creating gyration, then the mixing efficiency increases, but the thrust is reduced
Solution Approach 1:
The patent introduces grooves on the central body that generate a counter-gyratory flow to compensate for the gyration caused by the azimuthal component of the lobes. This preliminary anti-action prevents thrust loss by counterbalancing the rotational effect before it can significantly reduce the axial momentum of the exhaust flow.
Solution Approach 2:
The grooves create a counter-rotating flow that acts as an aerodynamic counterweight to the gyration induced by the lobes. This counter-flow balances the rotational momentum, allowing efficient mixing without significant thrust penalty.
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 mixer effectively reduces jet noise during takeoff in a compact design without sacrificing thrust, by enhancing mixing between external and internal air flows through the gyration and counter-rotation of air, thus meeting both drag and noise reduction requirements.
Implementation Method 1
the lobes having the same azimuthal component in the same direction so as to give a gyratory movement to the external air admitted into the convergence zone
Implementation Method 2
the grooves having the same azimuthal component in the same direction which is opposite to that of the azimuthal component of the lobes
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a variable-area flow mixer for a supersonic aircraft turbofan engine, comprising a central body (4), a primary cowl, a secondary cowl, and a nozzle (16) arranged in line with the secondary cowl. The nozzle has a plurality of external air intake openings (20) in which lobes (22) are mounted, movable between two positions: a closed position in which they obstruct the openings and an extended position in which they uncover said openings and extend into the nozzle to allow external air intake. The lobes have the same azimuthal component in the same direction, and the mixer further comprises a plurality of longitudinal grooves (36) extending over at least a portion of the central body, the grooves having the same azimuthal component in the same direction, which is opposite to that of the azimuthal component of the lobes.