Inter-turbine duct variable area ratios
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Solution Overview
Problem
Conventional gas turbine engines face challenges in designing inter-turbine ducts that balance size and boundary layer separation, leading to suboptimal performance due to increased radial angles and pressure losses.
Innovation Solution
The inter-turbine duct is designed with a hub and shroud configuration that converges in one portion and diverges in another, maintaining a specific meridional area ratio to reduce air flow separation and pressure losses, using a constant or decreasing meridional area ratio in the forward portion and an increasing ratio in the aft portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the inter-turbine duct length is decreased to reduce engine size and weight, then the radial angle of the duct increases, but this causes boundary layer separation and pressure losses that adversely affect low pressure turbine performance
Solution Approach 1:
The inter-turbine duct is divided into multiple sections with different area ratios: a forward portion with a first area ratio and an aft portion with a second area ratio. This segmentation allows each section to be optimized for its specific flow conditions, enabling the duct to be shorter while preventing boundary layer separation through appropriate area expansion in the aft portion.
Solution Approach 2:
Different portions of the duct are given different geometric properties - the forward portion has one area ratio configuration while the aft portion has another. This local differentiation allows the duct to maintain compact overall length while providing the necessary flow area expansion downstream to prevent separation and pressure losses.
2Reliability
If the inter-turbine duct is designed with a compromise between size and boundary layer separation, then engine weight and efficiency are suboptimal, but elongated ducts reduce boundary layer separation
Solution Approach 1:
By dividing the duct into forward and aft portions with different area ratios, the design achieves effective boundary layer control without requiring an overall elongated duct configuration, thus reducing engine weight while maintaining flow quality.
Solution Approach 2:
The area ratio parameter is changed between different portions of the duct - the forward portion uses one ratio while the aft portion uses another. This parameter variation enables compact duct design that still prevents boundary layer separation by providing appropriate area expansion where needed.
3Ease of manufacture
If the inter-turbine duct uses a constant area ratio throughout, then manufacturing is simpler, but it cannot optimize flow conditions in different duct regions
Solution Approach 1:
The duct is segmented into forward and aft portions with different area ratios, allowing optimization of flow efficiency in each region while maintaining reasonable manufacturing complexity through a relatively simple two-section geometry.
Solution Approach 2:
Each portion of the duct is given the specific area ratio quality needed for its location - the forward portion for incoming flow and the aft portion for flow expansion. This local optimization improves overall flow efficiency while keeping the manufacturing approach straightforward.
Data Source
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AI summary
A turbine section (150) of a gas turbine engine is annular about a longitudinal axis (102). The turbine section includes a first turbine with a first inlet and a first outlet (162); a second turbine with a second inlet (172) and a second outlet; and an inter-turbine duct (180) extending from the first outlet (162) to the second inlet (172) and configured to direct an air flow from the first turbine to the second turbine. The inter-turbine duct (180) has a first station (290) with a first meridional area, a second station (292) with a second meridional area, and a third station (296) with a third meridional area. The first station (290) is upstream of the second station (292) and the second station is upstream of the third station (296), and the second meridional area is less than or equal to the first meridional area.