Profiled Structure Serrations for Aircraft Noise Reduction
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Solution Overview
Problem
Aero-acoustic management in aerodynamic profiled structures, such as turbomachine blades, faces challenges in reducing noise while minimizing aerodynamic losses and mechanical stresses, particularly in Ultra-High Bypass Ratio turbofan engines where the interaction of the fan wake with guide vanes and air intake beaks generates significant noise.
Innovation Solution
The introduction of serrations on the leading and trailing edges of these structures, with varying amplitudes and spacings that follow monotonic laws, covering only a partial length and transitioning smoothly to a smooth part, helps in noise reduction while limiting mechanical stresses and aerodynamic losses. The serrations are strategically placed to align with the evolution of the turbulence integral scale, and their amplitude and spacing respect specific ratios to ensure efficient acoustic and mechanical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If serrations are introduced on the leading and trailing edges of profiled structures, then noise levels are reduced, but mechanical stresses and aerodynamic losses increase
Solution Approach 1:
The patent applies local quality by implementing serrations only on specific portions of the leading and trailing edges rather than uniformly across the entire structure. The serrations are strategically positioned in zones where they provide maximum noise reduction while minimizing mechanical stress concentration and aerodynamic losses in critical areas.
Solution Approach 2:
The patent utilizes parameter changes by varying the amplitude, spacing, and distribution of serrations along the leading and trailing edges. By adjusting these geometric parameters, the design optimizes noise reduction effectiveness while controlling mechanical stresses and aerodynamic performance within acceptable ranges.
2Object-affected harmful factors
If serrations cover the entire length of the profiled structure, then noise reduction is maximized, but manufacturing complexity and mechanical constraints increase
Solution Approach 1:
The patent applies segmentation by dividing the leading and trailing edges into distinct zones: serrated portions and smooth portions. This segmentation allows the structure to benefit from noise reduction where needed while maintaining manufacturing simplicity and structural integrity in other areas, thereby reducing overall manufacturing complexity.
Solution Approach 2:
The patent implements partial action by applying serrations only to the extent necessary for effective noise reduction rather than covering the entire length. This partial application of serrations achieves sufficient acoustic performance while significantly reducing manufacturing complexity and mechanical constraints compared to full-length serrations.
3Power
If the fan diameter is increased in Ultra-High Bypass Ratio turbofan engines, then thrust efficiency is improved, but the distance between the fan and guide vanes is reduced, increasing noise interaction
Solution Approach 1:
The patent applies preliminary anti-action by equipping the guide vanes and air intake beak with serrated leading edges before the airflow from the large-diameter fan interacts with them. This preliminary design feature preemptively reduces the noise generated by the wake-fan interaction, allowing the engine to achieve high thrust efficiency with a large fan diameter without suffering from excessive noise interaction.
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 noise levels, minimizes mechanical stresses, and facilitates the integration of the profiled structures into their environment by aligning with the turbulence characteristics, thereby enhancing the overall performance and reducing manufacturing constraints.
Implementation Method 1
the serrations have variations in amplitude (d) and/or in spacing (L2) between two successive vertices of teeth or of depressions, said variations being monotonic... aligning with the evolution of the turbulence integral scale
Implementation Method 2
noise is mainly produced at the leading and/or trailing edge, more precisely at the depressions of the serrations where pressure fluctuations are more intense
Data Source
AI summary
A profiled structure for an aircraft or turbomachine is elongated in a direction in which the structure has a length exposed to an airflow and includes serrations defined by successive teeth and depressions. The serrations may be transverse to a leading edge and/or a trailing edge of the profiled structure and in the direction of elongation. Along the profiled leading edge and/or profiled trailing edge, the successive teeth and depressions may extend only over a part of the length exposed to the flow. The amplitude and/or spacing of the teeth may vary monotonically except for the few teeth nearest each end of the part, with a remaining part of the length being smooth.