Composite Airfoil Bulbous Root for Interdigitated Rotor
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Solution Overview
Problem
Attaching composite blades to an outer rotor in an interdigitated gas turbine engine rotor assembly poses challenges such as increased rotor thickness and stress concentrations, which are not effectively addressed by existing technologies.
Innovation Solution
A composite blade design with a bulbous root shape and chisel-shaped end surfaces that minimizes rotor thickness and stress concentrations, utilizing continuous CMC plies and sacrificial machine stock plies for precise attachment to the outer rotor, reducing weight and attachment stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If composite blades are attached to an outer rotor in an interdigitated rotor assembly, then weight is reduced and temperature capability is improved, but rotor thickness increases and stress concentrations occur at the attachment area
Solution Approach 1:
The composite blade root is divided into multiple functional segments: a bulbous root portion for attachment, end surfaces for contact with the rotor, and a transition section. This segmentation allows each portion to be optimized for its specific function, enabling thin rotor attachment while maintaining structural integrity and reducing stress concentrations.
Solution Approach 2:
The blade root features localized geometric variations including a bulbous portion with increased thickness at the attachment zone, and chisel-shaped end surfaces with specific orientations. These local quality changes concentrate material where needed for attachment strength while keeping the overall blade lightweight, and distribute stresses appropriately at the rotor interface.
2Weight of moving object
If composite blades are attached to an outer rotor in an interdigitated rotor assembly, then weight is reduced and temperature capability is improved, but stress concentrations occur at the attachment area
Solution Approach 1:
The blade root is pre-formed with a bulbous geometry and chisel-shaped end surfaces during manufacturing, creating built-in stress distribution features before attachment. This preliminary action ensures that stress concentrations are minimized from the outset rather than requiring post-attachment modifications or reinforcement.
Solution Approach 2:
The blade is constructed from composite materials with tailored fiber orientations and ply stacks that provide both weight reduction and enhanced attachment strength. The composite structure allows for anisotropic material properties that optimize both the lightweight requirement and the attachment strength requirement simultaneously.
3Power
If composite blades are attached to an outer rotor in an interdigitated rotor assembly, then efficiency and power output are improved, but device complexity increases due to specialized attachment structures
Solution Approach 1:
The attachment structure is merged with the blade root geometry itself, eliminating the need for separate attachment components or complex mechanical fastening systems. The bulbous root and chisel-shaped end surfaces are integrated directly into the blade structure, simplifying the overall device while maintaining the performance benefits of composite materials.
Data Source
AI summary
Rotor assemblies and methods for manufacturing airfoils for rotor assemblies are provided. For example, a rotor assembly comprises a rotary structure extending circumferentially about an axial centerline of a gas turbine engine and an airfoil having a root and a tip. The root is coupled to the rotary structure and has a bulbous shape. The airfoil is formed from a plurality of composite plies, a portion of which defines at the root first and second end surfaces, which are in contact with the rotary structure and together define a chisel-shaped end of the root. In another embodiment, a rotor assembly comprises an outer rotor extending circumferentially about an axial centerline of a gas turbine engine and a composite outer rotor blade having a root and a tip. The blade root is coupled to the outer rotor and extends inward along a radial direction toward the axial centerline.