Downstream Surface Contours for Propeller Wake Noise Reduction
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Solution Overview
Problem
Unsteady aerodynamic interactions between propellers and downstream surfaces in aircraft propulsion assemblies lead to additional sound generation and reduced aerodynamic efficiency, challenging existing designs to effectively mitigate these issues across varying operational conditions.
Innovation Solution
The introduction of a surface modification element that defines a modified contour on aircraft surfaces positioned downstream of propellers, decorrelating the phase distribution of sound sources within the source field generated by propeller wakes and tip vortices, thereby reducing unsteady acoustic interactions and aerodynamic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a typical wing-mounted or fuselage-mounted propeller configuration is used, then the propulsion system achieves standard aerodynamic performance, but unsteady aerodynamic interactions between the propeller and downstream wing/pylon generate additional sound and reduce aerodynamic efficiency
Solution Approach 1:
The patent applies local quality by modifying only specific regions of the wing or pylon surface (downstream of the propeller) with contoured features, rather than redesigning the entire propulsion system. These localized surface modifications create specific flow patterns that reduce acoustic interactions while maintaining the overall standard propeller configuration and its manufacturing advantages.
Solution Approach 2:
The contoured surface features act as an intermediary element between the propeller wake and the wing/pylon surface. By introducing these intermediate geometric features, the patent mediates the interaction between the propeller and downstream structures, transforming the harmful unsteady aerodynamic interactions into more favorable flow patterns that reduce noise and improve efficiency.
2Ease of manufacture
If standard smooth surfaces are used downstream of the propeller, then manufacturing is simplified, but aerodynamic efficiency is reduced due to unsteady interactions with propeller wakes
Solution Approach 1:
Rather than making the entire surface complex, the patent introduces localized contoured features only in the regions most affected by propeller wakes (downstream areas of wings or pylons). This approach maintains ease of manufacture for the majority of the surface while providing targeted aerodynamic improvements where they are most needed.
Solution Approach 2:
The patent employs curved and contoured surface features rather than flat or angular geometries. These curved surfaces better accommodate the three-dimensional nature of propeller wakes and tip vortices, creating more effective flow management that enhances aerodynamic efficiency while remaining manufacturable using standard curving techniques.
3Device complexity
If conventional propeller-to-wing spacing is used, then the propulsion assembly achieves compact design, but higher harmonics of propeller blade passing frequency tones are dominated by interaction noise
Solution Approach 1:
The patent maintains compact overall spacing while introducing localized surface modifications at specific downstream locations. This allows the propulsion assembly to remain compact without increasing overall dimensions, while the localized features address the acoustic interaction problem in the critical regions where wakes impinge on the wing or pylon.
Solution Approach 2:
The patent converts the harmful acoustic interactions into beneficial effects by designing contoured features that transform the unsteady wake impingement into more favorable flow patterns. The same geometric features that would normally amplify higher harmonic tones are redesigned to promote flow attachment and reduce turbulence, thereby converting the harmful interaction into a benefit that reduces noise.
4Device complexity
If unmodified surfaces are used downstream of the propeller, then the design is simpler, but aerodynamic losses increase due to unsteady interactions
Solution Approach 1:
The patent reduces aerodynamic losses by applying surface modifications only in the specific regions where propeller wakes and tip vortices cause the most harm (downstream areas). This localized approach minimizes the increase in geometric complexity while targeting the exact locations where energy losses occur, thereby achieving better energy efficiency with minimal added complexity.
Solution Approach 2:
The contoured surface features are designed to dynamically interact with the unsteady propeller wakes and tip vortices. Rather than attempting to eliminate the unsteady nature of the flow, the features are shaped to adapt to and manage the dynamic wake structures, promoting flow attachment and reducing separation throughout the operational range, thereby minimizing aerodynamic losses.
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
This approach effectively reduces excess noise and enhances aerodynamic efficiency by decorrelating sound sources, leading to quieter operations and improved propulsion system integration.
Implementation Method 1
The modified contour is configured to decorrelate a phase distribution of a plurality of sound sources within a source field positioned on at least a portion of the surface
Data Source
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AI summary
An apparatus configured to reduce acoustic interactions between a propeller and a surface of an aircraft positioned downstream of the propeller includes a surface modification element of the surface of the aircraft. The surface modification element defines a modified contour of the surface. The modified contour is configured to decorrelate a phase distribution of a plurality of sound sources within a source field positioned on at least a portion of the surface.