Acoustic Liner Depth-to-Gap Ratio for Fan Buzz Saw Noise
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Solution Overview
Problem
Gas turbine engines experience significant 'buzz saw noise' during take-off and climb, primarily due to supersonic flow interactions with the fan, which existing acoustic liners have not adequately addressed, especially when the fan tip relative Mach number is around 1.2.
Innovation Solution
The design of a gas turbine engine incorporates an acoustic liner with a specific depth-to-gap ratio calculated using a desired reactance, optimized to attenuate fan blade passage frequency noise, where the depth-to-gap ratio is determined by the formula d/τ = tan(1 - X/2/πMtip, with Mtip ranging from 0.8 to 1.2, to effectively mitigate buzz saw noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing acoustic liners are used to attenuate fan noise, then some noise reduction is achieved, but the liners are too deep and do not effectively mitigate buzz saw noise when fan tip relative Mach number is around 1.2
Solution Approach 1:
The patent applies parameter changes by optimizing the depth-to-gap ratio of the acoustic liner based on the fan tip relative Mach number. The depth d is calculated using the formula d/τ = tan(1 - X/2/πMtip), where Mtip is the fan tip relative Mach number and X is the desired reactance. This parameter optimization enables effective buzz saw noise attenuation at shallower liner depths compared to existing designs, specifically targeting the critical Mach number range of 1.0 to 1.3 where buzz saw noise is most prominent.
2Object-affected harmful factors
If acoustic liners are made deeper to improve noise attenuation, then noise reduction performance improves, but the device complexity and space requirements increase
Solution Approach 1:
The patent optimizes the acoustic liner parameters by calculating the depth-to-gap ratio as a function of the fan tip relative Mach number and desired reactance. This parameter optimization achieves maximum noise attenuation at specific Mach numbers (1.0-1.3) without requiring excessive liner depth, thereby reducing device complexity and space requirements while maintaining effective noise control performance.
3Ease of manufacture
If acoustic liners are designed with fixed depth, then manufacturing is simplified, but they cannot effectively address buzz saw noise across varying Mach numbers
Solution Approach 1:
The patent establishes a design methodology where the acoustic liner depth-to-gap ratio is determined by the fan tip relative Mach number and desired reactance using the formula d/τ = tan(1 - X/2/πMtip). This approach allows the liner to be optimized for specific operating conditions while maintaining manufacturability. The formula provides a systematic way to adjust parameters based on expected operating Mach numbers, balancing manufacturing simplicity with adaptability across the critical Mach number range of 1.0 to 1.3.
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 substantially reduces buzz saw noise by targeting the fan blade passing frequency and associated acoustic modes, achieving maximum attenuation in the range of 0.035 to 0.08 for the depth-to-gap ratio, effectively addressing the noise issue across a range of Tip Relative Mach numbers from 1 to 1.3.
Implementation Method 1
Gas turbine engines are treated with acoustic liners to attenuate fan noise
Implementation Method 2
the depth-to-gap ratio is determined by the formula d/τ = tan(1 - X/2/πMtip, with Mtip ranging from 0.8 to 1.2, to effectively mitigate buzz saw noise
Data Source
Figure 1
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AI summary
A gas turbine engine has a propulsor including a fan and a liner positioned upstream of the fan. The liner has a backing plate, a cellular structure with cells extending from the backing plate, and a perforated sheet with a depth defined as a distance between the perforated sheet and the backing sheet. The depth is selected to achieve a desired ratio of the depth relative to a gap ?. A depth to gap ratio is substantially in a range of 0.035 to 0.08. A method is also disclosed.