Undulating Stator for Reducing Tonal Noise
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Solution Overview
Problem
Current designs for stators in propulsion units, such as those in bypass turbojets, fail to effectively reduce tonal noise generated by the interaction with rotors without compromising structural integrity or energy performance, especially when attempting to minimize flow disturbances and maintain fine fin structures.
Innovation Solution
The introduction of radial undulations on the stator's faces, with at least two bosses in the same azimuth direction, creates temporal phase oscillations in pressure fluctuations, introducing dephasing between the rotor's wake and the stator, thereby reducing noise amplification and distributing phase radiation geometrically to minimize harmonics associated with rotor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If radial undulations with large amplitude bosses are introduced on the stator face to dephase noise sources, then tonal noise is reduced, but the stator structural resistance may be compromised
Solution Approach 1:
The patent applies a thin undulating skin layer over the stator structure. This skin carries the radial undulations with amplitude up to 10cm for noise reduction, while the underlying core structure maintains structural integrity. The skin is sufficiently thin (not specifying exact thickness but implying it's much less than the undulation amplitude) to allow the undulations to effectively dephase noise sources, yet sufficiently strong to maintain aerodynamic performance without compromising overall stator strength.
2Object-affected harmful factors
If the stator is given inclined forms to dephase noise sources, then tonal noise is reduced, but the energy performance of the engine deteriorates
Solution Approach 1:
The patent applies undulations only on the external skin of the stator, leaving the internal core structure and flow passage geometry unchanged. This localized application allows noise reduction through dephasing at the noise-generating surface, while the flow passage maintains its optimized aerodynamic shape for energy efficiency. The undulations are confined to the outer surface where they affect noise radiation without interfering with the flow path.
3Object-affected harmful factors
If Helmholtz resonator cavities are integrated in the stator to damp acoustic excitations, then tonal noise is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces the complex Helmholtz resonator cavity system with a simpler undulating surface geometry. Instead of integrating three-dimensional cavities requiring thick stator structures and complex manufacturing, the solution uses radial undulations on the external skin that passively dephase noise sources through their geometric configuration alone. This substitution dramatically reduces manufacturing complexity while achieving comparable or superior noise reduction.
4Object-affected harmful factors
If radial undulations with large amplitude are applied to dephase noise sources, then tonal noise is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies that undulation amplitudes should be at least 1cm and can exceed 5cm or even reach 10cm, which is relatively large compared to typical aerodynamic tolerances. This excessive action approach ensures that the dephasing effect is robust and maintains effectiveness across varying operating conditions. The large amplitude provides a margin of safety against manufacturing variations, as the noise reduction mechanism remains effective even with moderate deviations from the nominal undulation geometry.
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 solution effectively attenuates tonal noise across various stator forms by dephasing noise sources, maintaining structural integrity and aerodynamic performance, even in three-dimensional profiles, while ensuring the stator can withstand operational forces.
Implementation Method 1
the crossing of said flow by the stator creates on said undulating surface pressure fluctuations with oscillations of the temporal phase according to the radial position
Implementation Method 2
introducing dephasing between the rotor's wake and the stator, thereby reducing noise amplification and distributing phase radiation geometrically
Data Source
AI summary
A stator designed to be placed radially in a flow which passes through one or more rotors which share the same axis of rotation, with a leading edge and a trailing edge. The leading edge and trailing edge are connected by a lower face and an upper face, wherein at least one of the faces of the stator has radial undulations which extend axially from the leading edge to the trailing edge. The radial undulations can have at least two bosses in the same azimuth direction, the amplitude of which is at least one centimeter on at least part of the axial length of the stator. A propulsion assembly formed by the rotor and the stator, and to a turbine engine comprising such assembly is also provided.