Variable Pitch Fan Turbofan Engine Bypass Flow Control
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Solution Overview
Problem
Existing gas turbine engines with variable pitch fans face suboptimal bypass flow conditions, leading to inefficiencies in propulsive efficiency and increased weight and drag due to larger fan diameters, which outweigh the benefits of improved efficiency.
Innovation Solution
A turbofan gas turbine engine system with a variable pitch fan (VPF) coupled to a speed reduction device and a low pressure compressor (LPC) with interdigitated variable pitch stator vanes, along with a modulating pressure relief valve and a controller to manage the geometry of the flowpath based on operational states and temperature, reducing weight and drag while maintaining propulsive efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the fan diameter is increased to improve propulsive efficiency, then the propulsive efficiency is improved, but the weight and drag of the engine increase
Solution Approach 1:
The patent applies variable pitch control to fan blades, allowing the pitch angle to be dynamically adjusted based on operational conditions. This enables the fan to maintain optimal aerodynamic performance across a wide range of speeds and loads, improving propulsive efficiency without requiring a larger fan diameter, thereby avoiding the associated weight penalty.
Solution Approach 2:
The patent changes the operational parameters of the fan system by introducing variable pitch capability and interdigitated stator vanes. These parameter changes allow the system to optimize airflow characteristics and thrust generation efficiency without increasing the physical dimensions of the fan, thus improving propulsive efficiency while maintaining acceptable weight.
2Use of energy by moving object
If the fan diameter is increased to improve propulsive efficiency, then the propulsive efficiency is improved, but the drag of the engine increases
Solution Approach 1:
Variable pitch control allows the fan blades to maintain optimal attack angles across different operating conditions, reducing airflow separation and turbulence. This dynamic adjustment improves thrust efficiency while minimizing drag-generating flow disturbances, allowing high propulsive efficiency without proportionally increasing drag.
Solution Approach 2:
By changing the pitch parameter of the fan blades and incorporating interdigitated stator vanes, the system optimizes the airflow field characteristics. This results in more efficient thrust generation with reduced wake turbulence and drag, achieving improved propulsive efficiency without the drag penalty associated with larger fan diameters.
3Ease of operation
If variable pitch fan blades are used to control thrust, then thrust control is improved, but the bypass flow condition becomes suboptimal
Solution Approach 1:
The patent merges the functionality of variable pitch fan blades with interdigitated stator vanes in the bypass duct. This combination allows the system to simultaneously achieve thrust control through fan pitch variation and bypass flow optimization through the stator vanes, which straighten and condition the bypass airflow to improve its efficiency and reduce turbulence.
Solution Approach 2:
The interdigitated stator vanes serve multiple functions: they condition the bypass flow to improve efficiency, work in conjunction with variable pitch blades for thrust control, and reduce flow instability. This multi-functionality allows the system to achieve both good thrust control and optimized bypass flow conditions simultaneously.
Data Source
AI summary
A method and system for a turbofan gas turbine engine system is provided. The gas turbine engine system includes a variable pitch fan (VPF) assembly coupled to a first rotatable shaft and a low pressure compressor LPC coupled to a second rotatable shaft. The LPC including a plurality of variable pitch stator vanes interdigitated with rows of blades of a rotor of the LPC. The gas turbine engine system also includes a speed reduction device coupled to said first rotatable shaft and said second rotatable shaft. The gas turbine engine system further includes a modulating pressure relief valve positioned between an outlet of said LPC and a bypass duct and a controller configured to schedule a position of said plurality of variable pitch stator vanes and said modulating pressure relief valve in response to an operational state of said turbofan gas turbine engine system and a temperature associated with said LPC.