Airfoil Root Conic Transition for Fatigue Resistance
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Solution Overview
Problem
Gas turbine engine airfoils are prone to damage from high cycle fatigue due to vibratory stress cycles caused by high rotational speeds and increased stage pressure ratios, leading to cracking and failure, necessitating an airfoil design that raises resonant frequencies to avoid damage.
Innovation Solution
The airfoil design features a root with a cylindrical neck, a conically shaped segment increasing cross-sectional area from the neck to the platform, and curved transitional portions, which increases stiffness and raises the resonant frequency of lower modes, positioning them outside the range of damaging vibratory excitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If airfoils are designed for high rotational speeds and higher stage pressure ratios, then productivity and power output are improved, but airfoils become subject to high tensile stress and vibrational modes causing fatigue damage
Solution Approach 1:
The patent modifies the geometric parameters of the airfoil root by introducing a conical transition section with specific dimensions (length L1, radius R1 at platform level, radius R2 at neck level). This geometric parameter change increases the area moment of inertia, thereby raising the resonant frequencies of the airfoil to avoid damaging vibratory excitations while maintaining high rotational speed operation
Solution Approach 2:
The patent employs a conical (curved) transition section instead of a straight or abrupt connection between the platform and the cylindrical neck. This curved geometry smoothly distributes stress concentrations and increases the area moment of inertia, enhancing the airfoil's resistance to fatigue damage while maintaining structural integrity at high rotational speeds
2Power
If airfoils operate at high rotational speeds, then power output increases, but resonant frequencies fall within the range of damaging vibratory excitations
Solution Approach 1:
The patent changes the geometric parameters of the root section by adding a conical transition with optimized dimensions (length L1, radii R1 and R2). This parameter modification increases the area moment of inertia, thereby raising the resonant frequencies of the airfoil modes outside the range of damaging vibratory excitations generated at high rotational speeds
Solution Approach 2:
The patent addresses the vibration problem by modifying the radial dimension of the root section through the conical transition. By increasing the area moment of inertia in the radial direction, the patent effectively changes the dimensional distribution of material, which raises the resonant frequencies without significantly affecting the aerodynamic performance in the flow direction
Data Source
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AI summary
A root extending from a platform of an airfoil is disclosed. The root may include a first portion having a generally cylindrical shape, and a second portion extending from the first portion to the platform. The second portion may have a circumference larger than a circumference of the first portion.