Variable Pitch Fan Exit Guide Vanes for Gas Turbine Engine Efficiency
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Solution Overview
Problem
Current gas turbine engines are oversized for cruise thrust conditions, leading to increased weight, performance, and fuel consumption penalties, as they are sized for maximum thrust requirements at top of climb and take-off conditions.
Innovation Solution
The implementation of an after-fan system with a variable pitch fan exit guide vane array and a short span after-fan turbine, which allows for independent adjustment of the fan exit guide vanes and optimized energy extraction across different flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the fan diameter is increased to increase engine Bypass Ratio for cruise propulsive efficiency, then cruise TSFC is improved, but the engine core size must be increased which increases engine/aircraft installation penalties
Solution Approach 1:
The fan exit guide vane system is segmented into multiple independently adjustable arrays (first variable pitch fan exit guide vane array and second variable pitch fan exit guide vane array) that can be controlled separately. This segmentation allows optimization of the bypass ratio for cruise conditions without requiring an increased fan diameter, as the variable pitch capability enables efficient energy extraction across different operating conditions.
Solution Approach 2:
The patent employs variable pitch fan exit guide vanes that can be independently adjusted in pitch according to operating conditions. The first and second variable pitch fan exit guide vane arrays are independently adjustable, allowing the system to adapt to different flight conditions (cruise vs. top of climb) dynamically. This dynamic adjustment enables the engine to maintain optimal performance across varying thrust requirements without oversizing the core.
2Power
If the fan diameter is increased by 45-50% to increase top of climb thrust, then required thrust is achieved, but engine weight and installation penalties increase
Solution Approach 1:
The patent changes the operating parameters of the fan exit guide vanes by making them variable pitch rather than fixed. The first and second variable pitch fan exit guide vane arrays can be independently adjusted to optimize performance at top of climb conditions. This parameter change allows the existing fan diameter to deliver maximum thrust capability without requiring a 45-50% increase in fan diameter, thereby avoiding the associated weight and installation penalties.
3Power
If the engine is sized for maximum thrust requirements, then top of climb and take-off performance is achieved, but cruise performance suffers due to oversizing
Solution Approach 1:
The variable pitch fan exit guide vane arrays enable the engine to dynamically adapt its performance characteristics. The first and second variable pitch fan exit guide vane arrays can be independently controlled to optimize the bypass ratio for cruise conditions while maintaining the capability to deliver maximum thrust when needed. This dynamic control allows the engine to be sized for maximum thrust without sacrificing cruise efficiency, as the system can operate at optimal points across the entire operating range.
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 solution enables a 6% reduction in Specific Fuel Consumption (SFC) and allows for a smaller fan diameter, reducing engine weight and installation penalties while maintaining efficient thrust production across various flight conditions.
Implementation Method 1
a variable pitch fan exit guide vane array that redirects bypass airflow from the fan section to an after-fan turbine
Implementation Method 2
an after-fan turbine that is operable to extract energy from the bypass airflow
Implementation Method 3
a splitter that divides the bypass airflow into a first stream and a second stream
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An after-fan system for a gas turbine engine includes a variable pitch fan exit guide vane array (62), an after-fan turbine (74) downstream of the variable pitch fan exit guide vane array (62) and a control (100) operable to vary a pitch of the variable fan exit guide vane array (62). A method of generating thrust for a gas turbine engine includes rotating a fan section (42) with an array of fan blades (82); rotating an after-fan turbine (74) downstream of the fan section (42); and varying a pitch of a variable fan exit guide vane array (62) downstream of the fan section (42) and upstream of the after-fan turbine (74).