Retractable Nonstreamlined Impeller Noise Reduction
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Solution Overview
Problem
Nonstreamlined dual impeller aircraft turbine engines generate high noise levels due to vortex interactions between impellers, which existing noise reduction methods fail to adequately address without compromising thrust and aerodynamic performance.
Innovation Solution
A retractable downstream impeller with a braking mechanism and pivot-mounted blades reduces its diameter during take-off and landing to minimize noise, while an epicyclic gear train maintains rotor power and thrust by compensating for the reduction with increased upstream impeller rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the diameter of the downstream impeller is reduced to avoid vortex interaction and reduce noise, then noise levels are reduced, but the thrust produced by the downstream impeller decreases
Solution Approach 1:
The downstream impeller is made retractable, allowing its diameter to be dynamically adjusted based on operational phase. During take-off and landing, the impeller is retracted to reduce vortex interaction and noise. During cruising, the impeller is extended to maximize thrust production, thus resolving the contradiction between noise reduction and thrust maintenance through temporal separation of functions.
2Force
If the load of the downstream impeller is increased to compensate for reduction in diameter, then thrust is maintained, but the aeromechanical complexity of the impeller pair design becomes extreme
Solution Approach 1:
Instead of increasing load on a small-diameter impeller, the system dynamically adjusts the impeller diameter itself. This avoids the need for extremely complex aeromechanical designs while maintaining thrust, as the impeller operates at optimal diameter during cruising and is simply retracted during noisy phases.
Solution Approach 2:
The impeller is segmented into multiple blades that can be independently positioned. This allows the impeller to be retracted by pivoting blades along the nacelle while maintaining structural integrity and simplifying the aeromechanical design compared to a fully variable geometry system.
3Object-generated harmful factors
If the downstream impeller is retracted during take-off and landing, then noise is reduced, but the power transmission system becomes more complex
Solution Approach 1:
The power transmission system merges the retraction mechanism with the existing epicyclic gear train. The brake is integrated into the gear train structure, acting on the planet carrier, which simultaneously controls both the retraction of the downstream impeller and the speed adjustment of the upstream impeller, thus reducing overall system complexity.
Solution Approach 2:
The epicyclic gear train serves multiple functions: it transmits power to both impellers, enables retraction of the downstream impeller through the brake mechanism, and allows speed compensation between the two impellers. This multi-functionality reduces the need for separate mechanisms and simplifies the overall power transmission system.
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 noise levels during critical phases while maintaining aerodynamic performance and thrust, adhering to strict acoustic certification standards and optimizing engine efficiency.
Implementation Method 1
the mechanism for actuating the downstream impeller in the retracted position comprises a brake for braking the rotation of the rotor
Implementation Method 2
the downstream impeller is driven by means of an epicyclic gear train. The gear train may drive both impellers. Thus the epicyclic gear train comprises planet gears mounted on a planet carrier between a ring gear and a central gear
Implementation Method 3
One means of actuating the blades into the retracted position includes for example spring means, not shown, which exert a force for tilting the blades about their pivot 71 in the downstream direction. These spring means are advantageously associated with a braking means 72 for braking the downstream impeller in order to form the mechanism for actuating the downstream impeller into the retracted position.
Data Source
AI summary
A turbine engine including two respectively upstream and downstream external impellers that are nonstreamlined, coaxial, and contrarotating is provided. The downstream impeller is retractable so as to reduce its diameter. The blades of the downstream impeller are mounted so as to pivot about a pivot, the axis of which forms a nonzero angle, notably perpendicular, with the axis of rotation of the impeller, the blades in the retracted position being tilted about the pivot.