Tie Shaft Coupled Axial Rotor Preload Control
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining dynamic stability and torque transmission due to the long span between supporting bearings, which requires proper preload and radial support to eliminate clearance and ensure rotational accuracy, especially in high-pressure rotor applications.
Innovation Solution
A tie shaft connection with a downstream hub providing radial support and a high-pressure compressor coupling nut for preload, along with a multi-layer interference fit and axial preload from a lock nut, ensures dynamic stability and torque transmission between compressor and turbine rotor stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a long span is used between supporting bearings to accommodate high-pressure rotor applications, then the rotor can span the distance between forward and aft supports, but dynamic stability and rotational accuracy are compromised due to clearance and potential whirling
Solution Approach 1:
A downstream hub is introduced as an intermediary component between the forward and aft bearings. This hub provides a middle support that divides the long span into shorter segments, thereby maintaining dynamic stability while accommodating the required span length for high-pressure rotor applications
Solution Approach 2:
The long span between supporting bearings is segmented by introducing a downstream hub with middle support. This divides the single long unsupported span into multiple shorter segments, each providing adequate radial support to maintain rotational accuracy and prevent whirling
2Device complexity
If a single coupling is used to join compressor rotors with welding or bolting, then torque transmission is simplified, but assembly complexity increases and adaptability decreases
Solution Approach 1:
The coupling system transitions from fixed welded or bolted joints to a dynamic preload-based friction connection. The axial preload creates adjustable friction forces that can accommodate variations in assembly conditions while maintaining torque transmission, thereby increasing adaptability without significantly increasing device complexity
3Manufacturing precision
If axial preload is applied to eliminate clearance in bearings, then rotational accuracy is improved, but the risk of whirling and dynamic instability increases
Solution Approach 1:
The downstream hub with middle support acts as a counterbalancing element that provides radial support to counteract the destabilizing effects of axial preload. This middle support prevents whirling while maintaining the axial preload necessary for rotational accuracy, effectively balancing the competing requirements
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 achieves reliable assembly and operation of gas turbine engines by maintaining dynamic stability and torque transmission with minimal radial envelope and low-profile locking, even at high speeds exceeding 20,000 RPM, while preventing whirling and ensuring a leak-proof joint.
Implementation Method 1
a single coupling which applies an axial force through the compressor rotors stack to hold them together and create the friction necessary to transmit torque
Implementation Method 2
The aft support includes a multiple layer interference fit between the shaft and the most downstream turbine rotor. The multi-layer fit accomplishes simultaneously radial support for the rotors stack and dynamic stability for a high pressure spool
Data Source
AI summary
A middle support member is used to provide axial support and control to the tie shaft. The middle support member includes a high pressure compressor coupling nut that applies a preload that allows the high pressure compressor stack to be installed separately from the high pressure turbine rotor through a kickstand.