Geared Turbofan Compressor Rotor Blade Frequency Design
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Solution Overview
Problem
Gas turbine engines produce noise frequencies sensitive to human hearing due to fluid dynamic interactions between blade and vane rows, which are typically mitigated by controlling the vane-to-blade ratio, but this approach increases weight and reduces aerodynamic efficiency.
Innovation Solution
A gas turbine engine design featuring a gear reduction system that allows the fan drive turbine rotor to drive a compressor rotor with a specific blade count and rotational speed, ensuring the formula (blade count × rotational speed)/60 ≥ 5500 Hz, reducing noise sensitivity to human hearing without compromising efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the vane-to-blade ratio is controlled to be above a certain number (e.g., 1.5 or greater) to achieve acoustic cut-off and reduce noise propagation, then noise sensitivity to human hearing is reduced, but weight increases and aerodynamic efficiency decreases
Solution Approach 1:
The patent changes the operational parameters of the compressor rotor, specifically the rotational speed and blade count, to shift the blade passage frequency above 5500 Hz. This parameter change allows the use of lower vane-to-blade ratios (improving weight and efficiency) while still achieving noise reduction by moving the noise frequency out of the human hearing sensitivity range.
Solution Approach 2:
The patent introduces a gear reduction system that enables the compressor rotor to operate at higher speeds independently of the fan speed. This dynamic adjustment of rotational speed allows the blade passage frequency to be shifted above 5500 Hz, achieving noise reduction without being constrained by fixed vane-to-blade ratio requirements.
2Object-affected harmful factors
If the vane-to-blade ratio is controlled to be above a certain number (e.g., 1.5 or greater) to achieve acoustic cut-off and reduce noise propagation, then noise sensitivity to human hearing is reduced, but aerodynamic efficiency decreases
Solution Approach 1:
The patent changes the operational parameters of the compressor rotor, specifically the rotational speed and blade count, to shift the blade passage frequency above 5500 Hz. This parameter change allows the use of lower vane-to-blade ratios (improving weight and efficiency) while still achieving noise reduction by moving the noise frequency out of the human hearing sensitivity range.
Solution Approach 2:
The patent introduces a gear reduction system that enables the compressor rotor to operate at higher speeds independently of the fan speed. This dynamic adjustment of rotational speed allows the blade passage frequency to be shifted above 5500 Hz, achieving noise reduction without being constrained by fixed vane-to-blade ratio requirements.
3Object-affected harmful factors
If the gear reduction ratio is increased to allow greater flexibility in blade and speed selection, then noise frequencies sensitive to human hearing are reduced, but device complexity increases
Solution Approach 1:
The patent introduces a gear reduction system as an intermediary mechanism between the fan drive turbine rotor and the compressor rotor. This gear system mediates the speed relationship, allowing the compressor to rotate at higher speeds than the fan, thereby shifting the blade passage frequency above 5500 Hz and reducing noise sensitivity without requiring changes to the fan design.
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 design effectively reduces noise frequencies sensitive to human hearing while maintaining or improving aerodynamic efficiency, particularly in high-thrust engines, by allowing greater flexibility in blade and speed selection.
Implementation Method 1
A gear reduction effects a reduction in the speed of the fan relative to an input speed from the fan drive turbine rotor that drives the compressor rotor
Implementation Method 2
noise is produced by fluid dynamic interaction between the blade rows and the vane rows. These interactions produce tones at a blade passage frequency of each of the low pressure turbine rotors, the low pressure compressor rotors, and their harmonics
Data Source
AI summary
A gas turbine engine has a fan and a turbine having a fan drive turbine rotor. The fan drive turbine rotor drives a compressor rotor. A gear reduction effects a reduction in the speed of the fan relative to an input speed from the fan drive turbine rotor that drives the compressor rotor. The compressor rotor has a number of compressor blades in at least one of a plurality of rows of the compressor rotor. The blades operate at least some of the time at a rotational speed. The number of compressor blades in at least one row and the rotational speed are such that the following formula holds true for at least one row of the compressor rotor turbine: (number of blades×rotational speed)/60 s≧5500 Hz, and the rotational speed is in revolutions per minute. A method of designing a gas turbine engine and a compressor module are also disclosed.