Serrated Flow-Splitter Nose for Turbofan Broadband Noise Reduction
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Solution Overview
Problem
In Ultra-High Bypass Ratio turbofan engines, the interaction between the fan wake and stationary guide vanes generates dominant broadband noise sources, necessitating new solutions to reduce noise levels.
Innovation Solution
A serrated profile with specific undulation geometry on the leading edge of the annular dividing wall's slat, optimizing the spacing and orientation of teeth and depressions to minimize noise radiation, including criteria such as integral length scales of airflow and angular positioning relative to guide vanes, to reduce turbulence and noise correlation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the axial distance between the slat and the trailing edge of the fan blades is reduced to increase fan diameter and reduce suspension pod length, then the engine compactness is improved, but the noise level increases due to stronger interaction between fan wake and slat
Solution Approach 1:
The slat leading edge is given a serrated curved profile with sinusoidal or triangular undulations instead of a straight edge. This curvature modifies the flow interaction with fan wake, reducing broadband noise generation while maintaining the reduced axial distance for engine compactness
Solution Approach 2:
The leading edge geometry is changed by introducing specific undulation parameters (amplitude h, wavelength λ) that optimize noise reduction. The amplitude and wavelength are dimensioned according to integral length scales of the airflow to minimize correlation between noise sources and turbulence
2Object-generated harmful factors
If a serrated profile with undulations is introduced on the slat leading edge, then the noise radiation is reduced by minimizing correlation between noise sources and turbulence, but the device complexity increases
Solution Approach 1:
The serrated profile uses simple sinusoidal or triangular wave patterns that can be manufactured with standard techniques. The curvature is defined by two parameters (amplitude and wavelength) rather than complex multi-dimensional geometry, keeping manufacturing feasible
Solution Approach 2:
The leading edge is segmented into repeating elementary geometries with identical undulations. This periodic segmentation allows the complex noise reduction function to be achieved through simple repeating units rather than a uniquely complex shape
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 serrated profile effectively reduces noise radiation by minimizing the correlation between noise sources and turbulence, optimizing airflow interaction with guide vanes, and reducing mechanical stress, thereby lowering overall noise levels.
Implementation Method 1
the interaction of the wake generated by the fan with the IGVs, the OGVs and the slat is one of the dominant broad band sources of noise
Implementation Method 2
For aerofoils having a serrated, i.e. undulated, leading edge, irrespective of the shape of the undulations, the interaction noise having turbulent flow is generated in particular at the depressions of the undulations, where the pressure fluctuations are more intense
Data Source
AI summary
A front fan turbomachine includes an annular separating wall having a slat for separating an air flow between a primary flow and a secondary flow, the slat having a leading edge; inlet guide vanes (IGV) for guiding the primary flow and outlet guide vanes (OGV) blades for guiding the secondary flow. The leading edge of the slat has a serrated profile having a succession of teeth and depressions.