Transition Piece Cooling Air Channel Design for Gas Turbine Stress Reduction
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Solution Overview
Problem
Conventional transition pieces in gas turbines suffer from thermal fatigue, oxidation, and creep deformation due to high temperatures and pressure differences, leading to damage and deformation, especially near the picture frame, where the cooling air pressure is higher than the combustion gas pressure, causing uneven stress and increased heat transfer coefficients.
Innovation Solution
A transition piece with a double-shell structure featuring a cooling air channel with a gradually decreasing cross-sectional area, increasing from a throat portion to a high-velocity zone and then recovering to a pressure recovery zone, which increases the cooling air velocity and heat transfer coefficient, reducing the differential pressure and stress on the inner duct, and using larger ejection holes and channel guides to enhance cooling efficiency and uniform flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the inner duct is cooled by impingement cooling holes with cooling air ejected onto the outer surface, then the cooling effect is improved, but the differential pressure between cooling air side and combustion gas side increases causing deformation
Solution Approach 1:
The patent changes the geometric parameters of the cooling air channel, specifically creating a converging section that increases cooling air velocity and a diverging section that recovers pressure. This parameter optimization allows maintaining effective cooling while reducing the differential pressure that causes deformation.
Solution Approach 2:
The patent introduces dynamic flow control by creating a cooling air channel with varying cross-sectional area that accelerates cooling air through a converging section. This dynamic approach optimizes the balance between cooling effectiveness and pressure differential.
2Ease of manufacture
If the cross-sectional area of the cooling air channel is uniform, then the manufacturing is simplified, but the cooling air velocity is insufficient and pressure recovery is poor
Solution Approach 1:
The patent employs curved streamlines in the cooling air channel design, with a converging section that smoothly accelerates flow and a diverging section that recovers pressure. The curved geometry optimizes flow dynamics while maintaining manufacturability through standard forming techniques.
3Stability of the object's composition
If the inner duct has non-circular cross section connected to turbine, then the flow distribution is improved, but the deformation resistance decreases due to external pressure
Solution Approach 1:
The patent applies different structural characteristics to different sections of the inner duct. The upstream section maintains circular cross-section for strength, while the downstream section transitions to non-circular for flow distribution. Reinforcement ribs are added locally at the picture frame area to strengthen the weaker non-circular section.
4Quantity of substance
If the cooling air channel has large ejection holes, then the cooling air flow is improved, but the structural integrity of the outer duct is reduced
Solution Approach 1:
The patent divides the cooling air delivery system into multiple smaller ejection holes distributed around the outer duct circumference. This segmentation provides sufficient total cooling air flow while maintaining structural integrity, as each individual hole is small and their collective effect achieves the required cooling.
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
The solution effectively suppresses deformation and enhances cooling efficiency, reducing thermal stress and pressure differences, thereby improving the durability and performance of the transition piece by optimizing the flow and pressure dynamics within the transition piece.
Implementation Method 1
a cooling air channel 50 that is formed between the inner duct 20 and the outer duct 30 and through which the air ejected from the ejection holes 31 flows
Implementation Method 2
ejected onto an outer peripheral surface at an outlet side of the inner duct 20 formed therein
Implementation Method 3
The channel cross-sectional area of the cooling air channel 50 gradually decreases at a cooling air flow downstream side rather than a portion where the ejection holes 31 are formed
Data Source
AI summary
A transition piece 10 in an embodiment is provided with an inner duct 20 through which a combustion gas is led to a turbine part 130 and an outer duct 30 that is provided so as to cover an outer periphery of the inner duct 20 and has a plurality of ejection holes 31 to eject air onto an outer peripheral surface of the inner duct 20 formed therein. It is structured such that a channel cross-sectional area of a cooling air channel 50 that is formed between the inner duct 20 and the outer duct 30 and through which the air ejected from the ejection holes 31 flows gradually decreases at an air flow downstream side rather than the portion where the ejection holes 31 are formed, and gradually increases from a throat portion 60 having the minimized channel cross-sectional area to an air flow downstream side.