Steam Turbine Last Stage Flow Instability Control
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Solution Overview
Problem
Steam turbines experience rotating flow instabilities and vibrations in the last stage rotor blades during low volumetric flow conditions, leading to inefficiencies and potential failure of other stages, with existing solutions either costly or inefficient.
Innovation Solution
A configuration with circumferentially shaped passages in the vane carrier of the steam turbine, blowing fluid onto the rotor blades at specific angles to stabilize the flow, reducing vibrations and resonance, with the fluid injection angle ranging from zero to -90 degrees, and the passages covering approximately 80% of the blade height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the last stage low pressure channel is removed and replaced with a perforated plate, then rotating flow instabilities are reduced, but steam turbine efficiency is greatly reduced and cost increases
Solution Approach 1:
The invention divides the flow control function into multiple segments: the circumferential groove segments the flow path, multiple bores segment the fluid injection points around the circumference, and this segmentation allows comprehensive coverage of the rotor blade leading edge to effectively control rotating flow instabilities while preserving turbine efficiency
Solution Approach 2:
The invention introduces a circumferential groove as an intermediary structure between the stator blades and rotor blades. This groove, combined with bores that inject fluid, acts as a mediator to modify the flow field and eliminate rotating instabilities without requiring removal of the low pressure channel, thus maintaining efficiency
2Temperature
If cold steam is delivered into the tip recirculation zone to reduce windage heating, then windage heating is reduced, but the complexity of the diaphragm assembly increases with multiple bores and grooves
Solution Approach 1:
The invention merges the windage heating control function with the rotating instability control function into a single integrated diaphragm assembly structure. The same circumferential groove and bore system that controls rotating instabilities also delivers cold steam to reduce windage heating, eliminating the need for separate cooling structures and reducing overall complexity
Solution Approach 2:
The diaphragm assembly with circumferential grooves and bores serves multiple functions simultaneously: it controls rotating flow instabilities by injecting fluid onto the rotor blade leading edge, and it reduces windage heating by delivering cold steam into the tip recirculation zone. This multi-functionality reduces the need for additional separate components
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 effectively eliminates rotor blade vibrations and resonance, maintaining efficiency at full-load conditions without the drawbacks of previous solutions, as demonstrated by tests showing reduced vibrational amplitude and dynamic stress.
Implementation Method 1
Through these passages 20, a fluid is blown onto the rotor blades 2
Implementation Method 2
the flow is centrifuged radially outwards in the rotor blades
Data Source
Figure 1~2
Figure 3
Figure 4a
AI summary
Configuration (10) of the last stage of a steam turbine where rotor blades (2) rotate encircled by a vane carrier (1), such that a plurality of passages (20) are located in the vane carrier (1), such that a fluid is blown through these passages (20) forming a flow that impinges onto the rotor blades (2), the number of passages (20), the location of the passages (20) in the vane carrier (1) and the velocity of the flow impinging onto the rotor blades (2), being calculated in such a way that rotating flow instabilities in the rotor blades (2) when the steam turbine operates at low volumetric flow conditions are avoided.