Variable Pitch Bladed Disc Asymmetry for Noise Reduction
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Solution Overview
Problem
Turbine engine propellers with uniformly distributed blades generate significant noise during take-off and approach phases, limiting acoustic certification and application due to the emergence of tone components over wide band noise, causing discomfort to the human ear.
Innovation Solution
A bladed wheel with variable pitch blades, where each blade has a unique tilt of its axis of rotation relative to the radial axis, distributing acoustic energy across multiple frequencies to reduce noise emergence and perceived discomfort, allowing for simultaneous pitch modification and untuning of blade frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blades are uniformly distributed and have identical geometrical configuration, then the aerodynamic operation is consistent and simple to manufacture, but significant noise is generated during take-off and approach phases
Solution Approach 1:
The patent applies asymmetry by giving each blade a different tilt angle relative to the radial axis. Specifically, at least one first blade has a first tilt and at least one second blade has a second tilt different from the first tilt, breaking the uniform symmetry of the blade arrangement. This asymmetric configuration distributes acoustic energy across multiple frequencies, reducing the emergence of tone components and lowering perceived noise levels during critical flight phases.
2Ease of operation
If all blades have the same pitch, then the propeller operation is simplified and easier to control, but noise certification is limited due to tone component emergence
Solution Approach 1:
The patent implements local quality by allowing each blade to have different local characteristics, specifically different tilts of their rotation axes relative to the radial axis. This means that while the blades can still be controlled through a common pitch mechanism, their individual local orientations differ, causing acoustic energy to be distributed across multiple frequencies rather than concentrated at a single tone, thereby enabling acoustic certification.
3Object-generated harmful factors
If blades are configured with different tilts, then acoustic energy is distributed across multiple frequencies reducing noise, but the device complexity increases
Solution Approach 1:
The patent applies dynamics by making the blade tilts adjustable rather than fixed. The variable pitch mechanism allows the tilts of the blades to be modified during operation, enabling the propeller to adapt its acoustic characteristics to different flight conditions. This dynamic capability allows noise reduction through distributed acoustic energy while maintaining manageable device complexity through a unified control mechanism.
Data Source
AI summary
A variable pitch bladed disc including a plurality of blades, each being of variable pitch about a blade axis of rotation and having a root, the plurality of blades including at least one first blade and at least one second blade, a plurality of rotor connecting shafts, each shaft having a root and a tip, the root of each blade being mounted on the tip of a corresponding rotor connecting shaft via a pivot so as to allow each blade to be rotated about the blade axis of rotation, the first blade having a first rotation axis inclination such that the rotation axis thereof is inclined in a fixed manner with respect to a radial axis passing through the root of the corresponding shaft, and the second blade has a second rotation axis inclination different from the first rotation axis inclination.