Turbomachine Rotor Segmentation for Tie Rod Frequency
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Solution Overview
Problem
Compressor rotors in turbomachines are limited by low natural frequencies of tie rods, which restrict achievable rotational frequencies and compressor power, due to the length and material properties of single central tie rods, and increasing tensile force is limited by material constraints to avoid damage.
Innovation Solution
Divide rotor segments into groups with additional bracing means to subdivide the tie rod into shorter sections, increasing natural frequencies and allowing higher rotational frequencies, using stepped tie rods and adjustable bracing components like nuts and threaded bores for precise force application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single central tie rod is used to connect rotor segments, then production and assembly simplicity is maintained, but the natural frequency of the tie rod becomes too low, limiting the rotational frequency and compressor power
Solution Approach 1:
The single central tie rod is segmented into multiple shorter sections by introducing additional bracing means between rotor segment groups. This segmentation reduces the free oscillation length of each tie rod section, thereby increasing the natural frequency to allow higher rotational frequencies and compressor power while maintaining the simplicity of a central tie rod structure
2Speed
If the tensile force on the tie rod is increased to raise natural frequency, then the natural frequency increases, but the material strength limit is exceeded, risking tie rod damage or breakage
Solution Approach 1:
Instead of increasing tensile force on a single long tie rod beyond material limits, the tie rod is segmented into multiple shorter sections. The natural frequency increases because the free oscillation length of each section is reduced, not because of increased tensile force. This allows achieving higher natural frequencies without exceeding the material strength of the tie rod
3Speed
If the length of the tie rod is reduced to increase natural frequency, then natural frequency increases, but the rotor cannot accommodate enough rotor segments to achieve desired compressor power
Solution Approach 1:
The tie rod is segmented into multiple sections by adding bracing means between rotor segment groups. This allows the overall rotor length to remain sufficient for accommodating multiple rotor segments (enabling desired compressor power) while each individual tie rod section remains short enough to provide high natural frequency. The segmentation decouples the conflict between overall length and section length
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 approach increases the maximum possible rotational frequency of the rotor without damaging the tie rod, maintaining simplicity in production and assembly like a single central tie rod, while preventing resonance oscillations by ensuring oscillation frequencies remain below natural frequencies.
Implementation Method 1
the natural frequency of the tie rod, in particular of a compressor rotor, which natural frequency is determined in principle by the dimensions and material properties of the tie rod and by the tensile force exerted on the tie rod with the aid of the bracing means
Implementation Method 2
oscillation frequencies equal to or close to the natural frequency of the tie rod are to be avoided since such resonance oscillations of the tie rod can impair the function of the turbomachine or can lead to damage/destruction of the tie rod
Data Source
AI summary
A rotor for a turbomachine, includes a plurality of axially adjacently arranged rotor segments which are each provided with a central opening, an individual tie rod extending through the openings of the rotor segments, and two holding devices which are arranged on axially opposing ends of the tie rod and hold the rotor segments together, the rotor segments forming at least two rotor segment groups between which at least one other holding device is arranged.