Mistuned Compressor Blades for Buzz Saw Noise Reduction

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Solution Overview

Problem

Gas turbine engine compressors generate annoying 'buzz saw' noise due to shock waves at the blade passing frequency, which current turbine inlet silencers only partially address, necessitating a new approach to reduce noise intensity effectively.

Innovation Solution

The compressor rotor blades are mistuned by varying their geometry parameters beyond manufacturing tolerances, shifting acoustic energy from the blade passing frequency to lower-amplitude harmonic frequencies, which are then preferentially absorbed by an inlet silencer, reducing overall noise intensity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If turbine inlet silencers are used to reduce compressor noise, then noise intensity at blade passing frequency is reduced, but the overall noise reduction is insufficient and buzz saw noise remains problematic

Engineering Contradiction:

Improvecompressor noiseVSAvoidnoise reduction effectiveness

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent changes the geometric parameters of compressor blades (pitch, axial sweep, lean angle, cutback) to create mistuned blades. This parameter modification shifts the acoustic energy distribution from a concentrated tone at blade passing frequency to multiple lower-amplitude tones at harmonic frequencies, thereby reducing the dominant noise component that silencers struggle to address effectively

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces asymmetry in blade geometry through mistuning, where individual blades are deliberately made non-uniform in their geometric parameters. This asymmetric configuration disrupts the coherent shock wave generation at blade passing frequency, scattering acoustic energy across multiple frequencies and improving overall noise reduction effectiveness

Inventive Principle:

Principle #4Asymmetry

2Productivity

If blade geometry parameters are made uniform within manufacturing tolerances, then compressor performance is optimized, but noise intensity at blade passing frequency increases

Engineering Contradiction:

Improvecompressor performanceVSAvoidnoise intensity at blade passing frequency

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent deliberately changes blade geometry parameters (pitch, axial sweep, lean angle, cutback) from uniform specifications to mistuned variations. This parameter modification maintains compressor performance while reducing noise intensity at blade passing frequency by shifting acoustic energy to multiple lower-amplitude harmonic frequencies

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful uniform blade geometry that generates intense concentrated noise into a beneficial mistuned configuration. By introducing controlled geometric variations, the intense blade passing frequency noise is transformed into multiple lower-amplitude tones, effectively converting a harmful acoustic characteristic into a more acceptable noise profile

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 significantly reduces noise intensity at the blade passing frequency and alters the subjective response to compressor noise, achieving a net decrease in total noise intensity, often by three decibels or more, while maintaining compressor performance.

Implementation Method 1

The mistuned blades reduce noise intensity at the blade passing frequency by shifting acoustic energy to multiple lower-amplitude tones

Methodology Applied

Scientific EffectAcoustic energy redistribution:

Implementation Method 2

The system is also configurable to be deployed with an inlet silencer that preferentially absorbs some of the shifted tones

Methodology Applied

Scientific EffectAcoustic absorption: Acoustic Absorption

Data Source

PatentUS8167540B2System for reducing compressor noise

Publication Date: 2012.05.01 HAMILTON SUNDSTRAND CORP

AI summary

A system for reducing compressor noise includes a rotor having a plurality of blades. The blades have a nominal geometry characterized by a blade parameter. At least some of the blades are mistuned, such that they differ from the nominal geometry by greater than a manufacturing tolerance in the blade parameter. The blades produce shock waves at a blade passing frequency, and the mistuned blades shift acoustic energy away from the blade passing frequency to multiple lower amplitude tones at other frequencies. The system is configurable to be deployed with an inlet silencer that preferentially absorbs acoustic energy at some of the shifted frequencies.