Turbine Last Stage Vane-to-Blade Ratio and Flow Constriction
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Solution Overview
Problem
Current turbine designs fail to effectively reduce noise emissions during noise-critical operating conditions, such as take-off and landing, due to limitations in the vane-to-blade ratio and flow cross-section management.
Innovation Solution
The design of a low-pressure turbine with a targeted vane-to-blade ratio and a convergent flow channel section to minimize the exhaust gas flow cross-section, particularly in the last stage, which reduces noise emissions by constriction of the exhaust gas stream within specific operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the vane-to-blade ratio is optimized to reduce noise emissions, then noise levels are reduced, but the flow cross-section management becomes insufficient
Solution Approach 1:
The patent applies parameter changes by optimizing the vane-to-blade ratio (V/B) to specific ranges (0.3-0.5 for single-stage turbines, 0.2-0.4 for multi-stage turbines) to shift blade-passing-frequency modes away from noise-critical ranges. Additionally, the flow cross-section area ratio (A2/A1) is changed to 0.6-0.8 to control exhaust gas flow and enhance noise reduction effectiveness.
Solution Approach 2:
The patent segments the turbine design into distinct optimization zones: the last stage with optimized vane-to-blade ratio, the convergent flow channel section with controlled area ratio, and the outlet guide grid. This segmentation allows each component to address specific aspects of noise control independently while working together systemically.
2Object-affected harmful factors
If the exhaust gas stream is constricted to reduce noise, then noise emissions are reduced, but the turbine efficiency may be compromised
Solution Approach 1:
The patent applies partial action by constricting the exhaust gas flow only in the last stage through the convergent flow channel section (area ratio 0.6-0.8), rather than throughout the entire turbine. This localized constriction is sufficient to reduce noise-critical blade-passing-frequency modes while minimizing impact on overall turbine efficiency and power output.
Solution Approach 2:
The patent implements local quality by applying different design optimizations to different parts of the turbine: the last stage features optimized vane-to-blade ratio and convergent flow channel for noise reduction, while upstream stages maintain conventional designs for efficiency. The outlet guide grid is also specifically optimized for the last stage's noise control function.
3Object-affected harmful factors
If the vane-to-blade ratio is placed in cut-off areas for blade-passing-frequency modes, then noise emissions are reduced, but the design flexibility is reduced
Solution Approach 1:
The patent establishes specific parameter ranges for the vane-to-blade ratio (V/B) that place the turbine operation in noise cut-off areas: 0.3-0.5 for single-stage turbines and 0.2-0.4 for multi-stage turbines. These parameter changes systematically shift the blade-passing-frequency modes away from noise-critical ranges while maintaining sufficient design flexibility within the specified ranges.
Data Source
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AI summary
The present invention relates to a method for designing a turbine of a gas turbine, in particular of an aircraft engine, which has a final stage with a rotating final turbine grid having several rotor blades (1) and a downstream adjacent stationary outlet guide vane grid having several guide vanes (2); wherein the final stage is characterized by a characteristic value vane-to-blade ratio ((V/B)TEC, 1; (V/B)TEC, 2) which specifies the ratio of the number of guide vanes to the number of rotor blades of the final stage; and wherein the final stage is designed such that this characteristic value vane-to-blade ratio ((V/B)TEC, 1;(V/B)TEC, 2) in a specified operating condition of the turbine above an upper cut-off limit (ok=-1) for mode k=-1 or between a lower cut-off limit (uk=-1) for mode k=-1 and an upper cut-off limit (ok=-2) for mode k=-2 or between a lower cut-off limit (uk=-2) for mode k=-2 and an upper cut-off limit (ok=-3) for mode k=-3 of a blade-passing frequency of the last stage at which its rotor blades rotate past one of its guide vanes; and that an exhaust gas flow (Q) passing through the last turbine grid in the specified operating condition is reduced before, in and/or after the outlet guide vane to a minimum flow cross-section (A2) which is at most 80% of its minimum flow cross-section (A1) in the last turbine grid.;