Asymmetric Annular Flow Guide for Steam Turbine Exhaust
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Solution Overview
Problem
High and intermediate pressure turbine exhaust hoods experience significant pressure loss due to spatial restrictions and turbulence, limiting their diffuser effect and efficiency compared to low pressure turbines, as conventional flow guides are not optimized for these pressures.
Innovation Solution
An annular flow guide with a vertically asymmetric shape is implemented, where the downstream flow guide portion is longer than the upstream portion, and the flow guide occupancy ratios are set between 0.6 and 0.7 for the downstream and 0.3 to 0.6 for the upstream portions, ensuring continuous occupancy ratios to prevent flow interruption and enhance rectification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a vertically symmetric annular flow guide is used in high and intermediate pressure turbines, then the structure is simple and easy to manufacture, but the pressure loss is high due to insufficient diffuser effect and flow turbulence
Solution Approach 1:
The flow guide is designed with a vertically asymmetric shape where the downstream flow guide portion is longer than the upstream portion. This asymmetric configuration allows the flow guide to effectively utilize the available space in the exhaust hood while providing sufficient diffuser effect to reduce pressure loss, resolving the contradiction between pressure loss reduction and structural simplicity
Solution Approach 2:
The flow guide is divided into upstream and downstream portions with different lengths, creating local quality variations. The downstream portion being longer provides enhanced diffuser effect where needed, while the upstream portion maintains structural simplicity, thereby reducing pressure loss without excessively increasing overall complexity
2Loss of energy
If the flow guide is elongated to enhance rectification effect, then pressure loss is reduced, but the flow passage may be blocked in high and intermediate pressure turbines due to spatial restrictions
Solution Approach 1:
By采用 vertically asymmetric shape with the downstream portion being longer, the flow guide maximizes its rectification effect within the limited space of high and intermediate pressure turbine exhaust hoods. This asymmetric design allows elongation in the downstream direction where space is available, enhancing pressure loss reduction without blocking the flow passage
Solution Approach 2:
The flow guide utilizes the vertical dimension by extending the downstream portion longer than the upstream portion. This dimensional differentiation allows the flow guide to achieve enhanced rectification effect without uniformly increasing the flow passage length, thereby avoiding blockage while reducing pressure loss
3Ease of manufacture
If conventional symmetric flow guides are used, then manufacturing is straightforward, but turbulence is not effectively reduced due to insufficient diffuser effect
Solution Approach 1:
The vertically asymmetric shape with the downstream portion being longer provides enhanced diffuser effect that effectively reduces turbulence and improves flow stability. While the shape is more complex than symmetric designs, it can still be manufactured using conventional methods, balancing manufacturing ease with flow stability improvement
Data Source
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AI summary
An exhaust system for a steam turbine provided with an improved annular flow guide in a high pressure or intermediate pressure turbine. The improved flow guide reduces flow turbulence in an exhaust hood and reduces pressure loss to thereby improve turbine plant efficiency. The shape (vertically symmetric) of a flow guide 5A according to a conventional technology was modified into the shape (vertically asymmetric) of a flow guide 5 such that the length of a downstream flow guide portion 5d is greater than that of a upstream flow guide portion 5u. Numerical analyses were performed to find the optimum flow guide occupation ratio of the conventional technology and the corresponding total pressure loss coefficient. The obtained values were used as reference values. Further, the flow guide occupation ratio of the upstream flow guide portion 5u was set at 0.4 and the flow guide occupation ratio of the downstream flow guide portion 5d was set at 0.7; at values where the total pressure loss coefficient becomes lower than the reference value. The rectification effect of the flow guide can thus be enhanced.