Low-Speed Balancing of Gas Turbine Compressor Rotors
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Solution Overview
Problem
Conventional low-speed balancing methods for gas turbine compressor rotors with compressor stage blades assemblies are inadequate as they fail to accurately balance the rotor for operational speeds due to blade movement within the assembly, leading to inconsistent unbalance measurements from one engine run to another.
Innovation Solution
A method for low-speed balancing that involves identifying and maintaining specific angular positions of blades to create sectors, introducing temporary inserts to stabilize blade positions, and adjusting movable blades to simulate operational conditions, allowing for accurate balancing without operating at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional low-speed balancing is performed on rotors with compressor stage blades assemblies, then the rotor can be balanced before installation, but blade movement within the assembly causes unbalance variation from run to run, making the balancing inaccurate for operational speeds
Solution Approach 1:
The patent applies preliminary action by performing balancing operations at simulated operational speeds rather than conventional low speeds. The rotor assembly is rotated at speeds that cause the blades to move to their operational positions, and balancing corrections are made while the blades are in these simulated operational positions. This preliminary positioning and balancing at operational speeds ensures that the same blade positions are replicated during actual operation, eliminating run-to-run variations.
Solution Approach 2:
The patent changes the rotational speed parameter from conventional low speeds (e.g., 800 rpm) to simulated operational speeds (e.g., 8000-14000 rpm or more). This parameter change causes the blades to move to their operational positions within the compressor stage blades assembly, where they remain stable during balancing measurements. By performing balancing at this elevated speed parameter, the blade positions during balancing match the blade positions during actual operation, ensuring consistent and accurate unbalance measurements.
2Ease of operation
If low-speed balancing is performed at speeds up to 20% of maximum rotational speed, then the rotor can be balanced without operating at high speeds, but the blades stay at different positions within the assembly compared to actual operation due to blade movement caused by operational speeds
Solution Approach 1:
The patent changes the rotational speed parameter from conventional low speeds (up to 20% of maximum) to simulated operational speeds (8000-14000 rpm or more, which is significantly higher). This parameter change transforms the blade positions from low-speed positions to operational positions, ensuring that the blades remain stable and in the same positions during both balancing and actual operation. The measurement precision is improved because the unbalance measurements are now taken at speeds that replicate actual operating conditions.
Data Source
AI summary
A method for low-speed balancing of a rotor having at least one compressor stage blades assembly includes a row of blades circumferentially arranged with circumferential clearance. Two or more blades are located blades, each having an angular position in the assembly, at which the located blades are maintained. The located blades define sectors. Each sector includes movable blades and sectoral circumferential clearances. The movable blades, for each sector, are circumferentially adjusted such that the sectoral circumferential clearance of the sector moves circumferentially downstream relative to the movable blades with respect to a rotational direction when the assembly is rotated. Relative position of the sectoral circumferential clearances and the movable blades within each sector is maintained by inserts. A measure of unbalance is determined for the rotor in low-speed balancing conditions. The inserts are removed after low speed balancing and the clearances are kept to accommodate the blade root thermal expansion.