Geared Turbofan Fan Blade Stagger Angle Variation
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Solution Overview
Problem
Geared turbofan engines face challenges in managing aerodynamic stability margin due to lower fan pressure ratios, which conventional methods to improve often result in performance, weight, or cycle penalties.
Innovation Solution
The design of fan blades with a greater difference in stagger angles between the mid-span and tip regions, along with varying camber angles, to enhance stability and efficiency, particularly suited for slower rotational speeds associated with geared fan configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional fan blade design with uniform stagger angles is used to maximize peak efficiency, then fuel efficiency is improved, but aerodynamic stability margin deteriorates
Solution Approach 1:
The fan blade is designed with non-uniform stagger angles where different radial sections have different stagger angles. Specifically, the stagger angle varies from the root to the tip of the blade, with the tip section having a larger stagger angle than the mid-span section. This local variation allows each section to operate at its optimal angle for stability while maintaining overall blade efficiency.
Solution Approach 2:
The invention changes the geometric parameters of the fan blade by introducing a specific stagger angle difference (20°-80°) between mid-span and tip regions. This parameter modification shifts the operating characteristics of the blade sections, allowing the tip section to operate away from its local peak efficiency point but with improved stability margin.
2Reliability
If more fan blades or greater blade chords are used to improve stability margin, then aerodynamic stability is improved, but weight and device complexity increase
Solution Approach 1:
Instead of uniformly increasing blade chord or number of blades, the invention applies local quality variation by adjusting stagger angles specifically in the tip region. This targeted geometric modification improves stability without requiring additional material or structural complexity throughout the entire blade.
Solution Approach 2:
The invention achieves stability improvement through parameter change (stagger angle variation) rather than through increasing blade quantity or overall size. This allows stability margin enhancement without the associated weight penalty of adding more blades or increasing chord dimensions.
3Use of energy by moving object
If fan blades are designed for peak efficiency at cruise conditions, then fuel consumption is reduced, but robustness against disturbances deteriorates
Solution Approach 1:
The fan blade design applies local quality differentiation where the tip section has a larger stagger angle than the mid-span section. This creates different operating characteristics along the blade span, with the tip section operating at a higher stagger angle that provides inherent robustness against disturbances while the mid-span maintains efficiency.
Solution Approach 2:
The non-uniform stagger angle design acts as a preemptive measure by building in stability margin at the blade tip before disturbances occur. The geometric configuration inherently resists stall and bird strike effects by operating away from the critical peak efficiency point where flow separation is more likely.
Data Source
AI summary
A fan stage of a ducted fan gas turbine engine has a rotor hub having a principal axis of rotation and a plurality of fan blades having a hub end attached to the hub and extending radially towards a tip end so as to define a blade span dimension. Each blade has a leading and a trailing edge, a chord for a section of the blade being a straight line joining the leading and trailing edges within the section. A difference between a stagger angle in a mid-span region and in the vicinity of the tip end of each blade is greater than or equal to 20°. The fan blades are twisted to a greater extent than conventional between the mid-span and tip end. A camber angle difference between the mid-span region and the tip end may be greater than 30 degrees.