Fan Rotor Blade Root Extension for Stress Reduction
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Solution Overview
Problem
In turbofan engines, increasing the bypass ratio to reduce fuel consumption and noise levels leads to increased engine weight due to larger fan diameters and hub/tip ratios, causing stress issues in the fan rotor blade and spin cone when using conventional dovetail structures.
Innovation Solution
A fan rotor blade support structure where the upstream end of the extension part at the root is a free end, radially outside the fan rotor blade tip, supporting centrifugal forces directly via the rotary disk and preventing excessive stress in both the root and spin cone, with a rib structure to suppress deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bypass ratio is increased to reduce fuel consumption and noise levels, then fuel efficiency and noise reduction are improved, but engine weight increases due to larger fan diameters and hub/tip ratios
Solution Approach 1:
The fan rotor blade is segmented into multiple parts: blade body, root, extension part, and attached part. This segmentation allows the extension part to extend upstream without increasing the hub diameter, enabling larger effective fan diameter for higher bypass ratio while avoiding proportional increase in hub weight
Solution Approach 2:
The extension part extends in the axial direction (upstream direction) rather than radially outward, adding a dimensional component to the blade structure. This allows increasing the effective air intake area without proportionally increasing the hub/tip ratio, thus improving bypass ratio without linearly increasing engine weight
2Weight of moving object
If the hub/tip ratio is reduced to decrease engine weight, then engine weight is reduced, but structural strength and stress distribution in the fan rotor blade deteriorate
Solution Approach 1:
Dividing the blade into blade body, root, extension part, and attached part allows independent optimization of each segment. The extension part can be designed with appropriate thickness and reinforcement to maintain strength while contributing to weight reduction through optimized material distribution
Solution Approach 2:
Different parts of the blade have different structural characteristics optimized for their specific functions. The extension part has localized reinforcement where needed, the root has optimized attachment geometry, and the blade body has aerodynamic shaping. This local optimization maintains overall structural strength while reducing unnecessary weight
3Area of stationary object
If the extension part is made long to increase air intake area, then bypass ratio is improved, but stress concentration at the root increases
Solution Approach 1:
Separating the extension part from the root with a clearly defined attached part creates distinct stress zones. The attached part is designed as a transition zone that gradually transfers loads, preventing stress concentration at the root while allowing the extension part to contribute to air intake area
Solution Approach 2:
The attached part acts as an intermediary element between the root and the extension part. It serves as a transition zone that smoothly transfers mechanical loads from the extended blade structure to the root, preventing stress concentration while enabling the extension part to increase air intake area
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 configuration effectively supports centrifugal forces on the fan rotor blade while preventing excessive stress in the root and spin cone, even at a hub/tip ratio of 0.35 or less, maintaining structural integrity and reducing weight.
Implementation Method 1
supporting centrifugal forces directly via the rotary disk
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The fan rotor blade (73) has a root (73a) located at an end at the side of a rotary disk (75), and a tip (73b) located at an outer end in a radial direction of the rotary disk (75), and extends from the root (73a) to the tip (73b). The root (73a) has an attached part (93) attached to a rotor blade fixing part (75a) of the rotary disk (75), and an extension part (95) extending from the attached part (93) toward the upstream side. An upstream end of the extension part (95) is a free end.