Geared Turbofan Low Noise Compressor and Turbine
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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 difficult to mitigate without compromising weight and aerodynamic efficiency.
Innovation Solution
A gas turbine engine design featuring a gear reduction system that allows the fan and low pressure compressor to operate at distinct speeds, with a formula (number of blades × rotational speed)/60 ≥ 5500 Hz to minimize noise frequencies sensitive to human hearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a vane-to-blade ratio of 1.5 or greater is used to achieve acoustic cut-off and reduce noise, then noise propagation is prevented, but weight increases and aerodynamic efficiency decreases
Solution Approach 1:
The patent changes the operational parameters by using a gear reduction system to operate the fan at a different speed than the low pressure compressor, allowing the blade and vane counts to be optimized for aerodynamic efficiency rather than being constrained by noise propagation requirements. This parameter change enables the system to achieve noise control through speed differentiation rather than through increased structural complexity.
Solution Approach 2:
The patent introduces dynamic operation by allowing the fan and low pressure compressor to rotate at different speeds via the gear reduction system. This dynamic approach enables the blade passage frequencies to be shifted away from sensitive human hearing ranges without requiring fixed structural modifications that would increase weight.
2Object-affected harmful factors
If a vane-to-blade ratio of 1.5 or greater is used to achieve acoustic cut-off, then noise propagation is prevented, but aerodynamic efficiency decreases
Solution Approach 1:
The patent changes the operational parameters by using a gear reduction system to operate the fan at a different speed than the low pressure compressor, allowing the blade and vane counts to be optimized for aerodynamic efficiency rather than being constrained by noise propagation requirements. This parameter change enables the system to achieve noise control through speed differentiation rather than through increased structural complexity.
Solution Approach 2:
The patent introduces dynamic operation by allowing the fan and low pressure compressor to rotate at different speeds via the gear reduction system. This dynamic approach enables the blade passage frequencies to be shifted away from sensitive human hearing ranges without requiring fixed structural modifications that would reduce aerodynamic efficiency.
3Device complexity
If the low pressure turbine drives both the low pressure compressor and fan at the same speed, then the system is simpler, but noise frequencies fall within the sensitive human hearing range
Solution Approach 1:
The patent introduces a gear reduction system as an intermediary mechanism between the low pressure turbine and the fan. This intermediary allows the fan to be driven at a different speed than the low pressure compressor, shifting the noise frequencies away from the sensitive human hearing range while maintaining reasonable system complexity through the use of established gear reduction technology.
Data Source
AI summary
A gas turbine engine has a fan, a turbine section having a first turbine including a first turbine rotor, a compressor rotor, and a gear reduction configured to effect a reduction in a speed of the fan relative to an input speed from the first turbine rotor. Each of the compressor rotor and the first turbine rotor includes a number of blades in each of a plurality of blade rows, the number of blades configured to operate at least some of the time at a rotational speed, and the number of blades and the rotational speed being such that the following formula holds true for at least a majority of the blade rows of the first turbine rotor, but does not hold true for any of the blade rows of the compressor rotor: (number of blades×rotational speed)/60≧5500, and the rotational speed being an approach speed in revolutions per minute.