Variable Area Fan Nozzle for Gas Turbine Noise Reduction
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Solution Overview
Problem
Gas turbine engines, particularly those used in aircraft, face significant noise challenges due to fan operation, with existing designs failing to maintain optimal fan tip leading edge relative flow angles across various operating points, leading to inefficiencies and increased noise levels.
Innovation Solution
The design maintains the absolute value of the difference between the design point and off-design point fan tip leading edge relative flow angles within specific ranges (e.g., zero to five degrees), utilizing a variable area fan nozzle and geared architecture to control airflow and tip speed, ensuring optimal incidence angles and reduced noise across acoustic operating points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the fan operates at high speed to increase power output, then the power increases, but the fan noise increases significantly
Solution Approach 1:
The patent applies dynamics by making the fan nozzle area variable rather than fixed. The fan nozzle area is adjusted dynamically based on operating conditions to maintain optimal flow angles across different power settings. This allows the fan to operate efficiently at various speeds while minimizing noise generation, particularly at part-power conditions where noise is most problematic relative to power output.
Solution Approach 2:
The patent changes physical parameters by controlling the fan nozzle area and fan tip speed ratio to maintain the fan tip leading edge relative flow angle within a specific range (0-5 degrees from design point). By adjusting these parameters dynamically, the system achieves reduced noise emission while maintaining required power output levels across different operating conditions.
2Device complexity
If the fan nozzle area is fixed to simplify the system, then the device complexity is reduced, but the fan cannot maintain optimal flow angles at off-design points, increasing noise
Solution Approach 1:
The patent transforms the static fan nozzle into a dynamic component whose area can be adjusted. This dynamic adjustment capability allows the system to adapt to different operating conditions (part-power, full-power, approach, takeoff) and maintain optimal flow angles, thereby reducing noise without requiring overly complex control systems.
Solution Approach 2:
The variable fan nozzle area mechanism serves multiple functions: it controls flow angle at different power settings, optimizes fan efficiency across the operating range, and reduces noise emission. This multi-functionality justifies the added complexity by delivering comprehensive performance improvements across all operating conditions.
3Productivity
If the fan tip speed is increased to improve efficiency, then the engine efficiency increases, but the fan noise increases
Solution Approach 1:
The patent optimizes the relationship between fan tip speed and nozzle area by treating them as interconnected variables. By adjusting the fan tip speed ratio and nozzle area together to maintain optimal flow angles, the system achieves high efficiency while minimizing noise. This coordinated parameter adjustment allows the fan to operate at efficient speeds without proportionally increasing noise.
Data Source
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AI summary
In accordance with one aspect of the disclosure, a gas turbine engine, method of using and designing such is disclosed. The gas turbine engine may comprise a fan including a plurality of blades, and a variable area fan nozzle. The fan may be configured to have a design point fan tip leading edge relative flow angle PADP, and may be further configured to have an off-design point fan tip leading edge relative flow angle β at an off-design fan operating point. The variable area fan nozzle may be configured to manipulate the amount of air flowing through the fan so that the absolute value of a difference between the design point fan tip leading edge relative flow angle PADP and the off-design point fan tip leading edge relative flow angle β is in a specified range.