Gas Turbine Fan Blade Root Zone of Weakness Impact Management
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Solution Overview
Problem
Current designs for turbofan gas turbine engines face challenges in managing the impact of detached fan blades, which require additional material reinforcement in the fan casing to absorb the energy of the remaining blade portion, leading to increased weight and potential moisture path issues in composite materials.
Innovation Solution
Incorporating a root former with a zone of weakness, such as a line of separation or a space defined between adjacent root former parts, to reduce the root part's ability to withstand impact forces, allowing for controlled break-up and reduced load on the fan casing, thereby minimizing the need for additional reinforcement and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional material reinforcement is provided in the rear fan containment region to contain the remaining blade portion, then the containment capability is improved, but the weight of the turbofan gas turbine engine increases
Solution Approach 1:
The root part is divided into multiple root former parts with zones of weakness between them, allowing the root to segment and break up upon impact. This segmentation enables the blade to dissipate energy through controlled fragmentation rather than requiring the containment region to absorb all impact energy, thus reducing the reinforcement needed in the fan casing.
Solution Approach 2:
The mechanical properties of the root part are changed by introducing zones of weakness that reduce its ability to withstand transverse forces. This parameter change allows the root to fail in a controlled manner during impact, transforming it from a rigid structure that transmits full impact force to a more compliant structure that dissipates energy through progressive collapse.
2Weight of stationary object
If apertures or passages are drilled in the root to promote break up upon impact, then the reinforcement required in the casing is reduced, but moisture paths are created in composite materials leading to laminar cracking
Solution Approach 1:
Instead of creating through-drills or passages that penetrate the entire root structure, zones of weakness are introduced as localized features within the root former parts. These zones reduce material density and strength only in specific locations where break-up is desired, while maintaining the integrity of the surrounding composite material and preventing moisture infiltration paths.
3Strength
If the root part is designed with high strength to withstand operational loads, then the blade can handle higher forces, but the rear fan containment region requires more reinforcement to contain the blade upon detachment
Solution Approach 1:
The root part is designed with dynamic failure characteristics through the inclusion of zones of weakness that allow progressive collapse under impact loads. During normal operation, the root maintains sufficient strength, but upon detachment and impact, the zones of weakness enable controlled break-up that dynamically dissipates impact energy, reducing the static reinforcement requirements of the containment region.
Data Source
AI summary
A fan blade for a gas turbine engine has an aerofoil part and a root part. The root part includes a root former; the root former includes a zone of weakness, which reduces the ability of the root part to withstand an impact force. Thus, in an impact situation in which the fan blade has separated from the fan rotor and the fan blade has itself separated into fragments, the root part will fracture or buckle more easily than would be the case with conventional arrangements. This will lower the impact force of the root part upon the fan casing, thus permitting the fan casing to be designed to withstand lower impact forces. The fan casing can therefore be made lighter, and cheaper, than in conventional arrangements.