Mid-span shroud elliptical cross-section fan blade
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Solution Overview
Problem
Gas turbine engine fan sections experience self-induced oscillations or flutter, which can lead to airfoil fracture, and existing solutions to prevent this either increase engine weight or are not efficient in reducing flutter.
Innovation Solution
A fan blade design with a mid-span shroud having an elliptical cross-section where the distance from the center to the rotational axis varies along the length, reducing drag and weight by allowing more fan blades with decreased chord width, and eliminating the need for variable area fan nozzles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the chord width of fan blades is increased to prevent airfoil fracture from flutter, then the reliability is improved, but the weight of the engine increases
Solution Approach 1:
The fan blade is segmented into multiple parts: a blade body and a separate mid-span shroud that can be independently designed and positioned. This segmentation allows the shroud to provide structural reinforcement for flutter prevention while the blade body maintains optimized aerodynamic dimensions, preventing the need to increase overall chord width and thus avoiding weight increase.
Solution Approach 2:
The mid-span shroud acts as an intermediary structural element between adjacent fan blades. It provides the necessary stiffness and structural support to prevent airfoil fracture from flutter, while being separate from the main blade structure, allowing the blades themselves to maintain lighter, optimized dimensions without compromising reliability.
2Reliability
If the chord width of fan blades is increased to prevent airfoil fracture from flutter, then the reliability is improved, but the productivity decreases due to increased rotating mass
Solution Approach 1:
By segmenting the fan blade structure into blade bodies and separate mid-span shrouds, the invention allows the shrouds to provide flutter prevention functionality while the blade bodies maintain optimized, lighter dimensions. This reduces the rotating mass compared to increasing overall chord width, thereby improving power transfer efficiency and productivity.
3Ease of manufacture
If a mid-span shroud with constant cross-sectional area is used, then the manufacturing is simplified, but the aerodynamic drag increases
Solution Approach 1:
The mid-span shroud employs varying cross-sectional dimensions along its length rather than a constant cross-section. The cross-sectional area varies to optimize aerodynamic performance at different locations, reducing overall drag while still providing necessary structural support. This local variation in geometry balances manufacturing complexity with aerodynamic efficiency.
Solution Approach 2:
The cross-sectional parameters of the mid-span shroud (dimensions, area) are varied along its length to optimize aerodynamic drag. By changing these geometric parameters locally rather than maintaining constant dimensions, the shroud achieves reduced energy loss while maintaining structural integrity and manufacturability.
Data Source
Figure 1
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AI summary
The present invention relates to a fan (62) for a gas turbine engine (20) with a plurality of fan blades (42) rotatable about an axis (A), wherein each of the plurality of fan blades (42) includes a mid-span shroud (66) having first and second shroud members (68, 70) extending from the suction and the pressure surface of the fan blade (42) respectively. The shroud members (68, 70) have a varying cross-sectional area, the cross-section being preferably elliptical with a major axis (78) and a minor axis (76). The shroud section may comprise a cross-sectional area, which varies with the major axis (78) or the minor axis (76). The distance between the center (80) of the ellipse with respect to the rotational axis (A) may vary. Thus, drag of the mid-span shrouds (66) is substantially reduced.