Intermediate Turbine Rotor Noise Reduction via Blade Passage Frequency
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Solution Overview
Problem
Gas turbine engines face noise sensitivity issues due to fluid dynamic interactions between blade and vane rows, particularly in low pressure turbine and compressor sections, which are mitigated by controlling the vane-to-blade ratio but result in increased weight and reduced aerodynamic efficiency.
Innovation Solution
The design incorporates an intermediate pressure turbine with a specific blade count and rotational speed formula (number of blades × speed)/60 ≥ 5500 Hz to reduce noise sensitivity, allowing for a gear reduction system that drives a fan at a lower speed, thereby reducing noise frequencies sensitive to human hearing.
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, then noise sensitivity to human hearing is reduced, but weight increases and aerodynamic efficiency decreases
Solution Approach 1:
The patent changes the operating parameters of the intermediate pressure turbine by controlling the blade passage frequency to be at least 5500 Hz, which shifts the noise away from the sensitive human hearing range. This parameter change allows the use of a lower vane-to-blade ratio while still achieving acoustic cut-off, thereby reducing weight and improving aerodynamic efficiency without sacrificing noise mitigation.
2Object-affected harmful factors
If the vane-to-blade ratio is controlled to achieve acoustic cut-off, then noise sensitivity is reduced, but aerodynamic efficiency decreases
Solution Approach 1:
By establishing that the blade passage frequency of the intermediate pressure turbine shall be at least 5500 Hz, the patent changes the operational parameters to allow for a lower vane-to-blade ratio. This parameter change enables the system to maintain acoustic cut-off while improving aerodynamic efficiency, as the lower ratio reduces flow separation and improves blade row interaction.
3Object-affected harmful factors
If the number of turbine blades and rotational speed are increased to achieve higher blade passage frequency, then noise sensitivity is reduced, but the complexity of the turbine design increases
Solution Approach 1:
The patent establishes a clear parameter relationship: the blade passage frequency of the intermediate pressure turbine shall be at least 5500 Hz. This parameter change provides a design guideline that balances noise mitigation with practical design complexity, allowing engineers to select appropriate numbers of blades and rotational speeds that achieve the frequency target without excessive complexity.
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 effectively reduces noise frequencies sensitive to human hearing while maintaining aerodynamic efficiency and thrust production, applicable to high-bypass engines rated for 15,000 pounds of thrust or more.
Implementation Method 1
noise is produced by fluid dynamic interaction between the blade rows and the vane rows
Implementation Method 2
These interactions produce tones at a blade passage frequency of each of the low pressure turbine rotors
Implementation Method 3
The fan drive turbine drives a gear reduction to in turn drive a fan, and effects a reduction in the speed of the fan relative to an input speed from the fan drive turbine
Data Source
AI summary
A turbine section including a high pressure turbine, an intermediate pressure turbine and a fan drive turbine, the fan drive turbine driving a gear reduction to in turn drive a fan, and effecting a reduction in the speed of the fan relative to an input speed from the fan drive turbine and said high pressure turbine driving a high pressure compressor, and the intermediate pressure turbine driving a low pressure compressor, with the intermediate pressure turbine having a number of turbine blades in at least one row, and the turbine blades operating at least some of the time at a rotational speed, and the number of turbine blades in the at least one row, and the rotational speed being such that the following formula holds true for the at least one row of the intermediate pressure turbine: (number of blades×speed)/60?5500 Hz.