Blade Outer Air Seal Heat Shield Segmentation
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Solution Overview
Problem
Gas turbine engines face challenges in effectively sealing the radial gaps between blades and the annular shroud to minimize gas flow escape, which affects efficiency and performance.
Innovation Solution
A seal assembly comprising a rail shield with radially-extending sidewalls, a spring to bias the seal, and a seal arc segment with ramped interfaces, along with a carriage to support the seal arc segment, is used to create a robust and efficient sealing system around the rotor blades, utilizing a metallic alloy and ceramic materials for high thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the shroud is placed in close radial proximity to the blade tips to reduce gas flow escape, then sealing effectiveness is improved, but thermal stresses and heat exposure to the shroud increase
Solution Approach 1:
The shroud is divided into two distinct functional zones: an inner radially-extending sidewall portion that provides the sealing surface in close proximity to blade tips, and an outer shield portion that extends axially to protect the sealing portion from direct heat exposure. This segmentation allows each portion to optimize its function independently.
Solution Approach 2:
The shield portion acts as an intermediary protective barrier between the hot gas environment and the sealing sidewall portion. It intercepts direct fluid flow and thermal radiation, reducing heat transfer to the sealing surfaces while maintaining their functional proximity to the blade tips.
2Reliability
If the shroud is placed in close radial proximity to the blade tips to reduce gas flow escape, then sealing effectiveness is improved, but thermal stresses on the shroud increase
Solution Approach 1:
The shroud is divided into two distinct functional zones: an inner radially-extending sidewall portion that provides the sealing surface in close proximity to blade tips, and an outer shield portion that extends axially to protect the sealing portion from direct heat exposure. This segmentation allows each portion to optimize its function independently.
Solution Approach 2:
The shield portion acts as an intermediary protective barrier between the hot gas environment and the sealing sidewall portion. It intercepts direct fluid flow and thermal radiation, reducing heat transfer to the sealing surfaces while maintaining their functional proximity to the blade tips.
3Stress or pressure
If cooling is applied to the inner surface of the shroud to manage thermal stresses, then thermal management is improved, but the complexity of the cooling system increases
Solution Approach 1:
Cooling is applied selectively to the inner radially-extending sidewall portion where thermal stresses are most critical for sealing functionality, rather than cooling the entire shroud structure. This localized approach reduces thermal stresses where needed while minimizing the complexity and resource requirements of the cooling system.
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 reduces gas flow escape, maintains low stress concentrations, and allows for thermal management by cooling the inner surface without exposing the outer sidewalls to the fluid flow, thereby enhancing the engine's efficiency and reducing thermal stresses.
Implementation Method 1
a spring to bias the seal
Implementation Method 2
allows for thermal management by cooling the inner surface
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A seal assembly (60) includes a seal arc segment (66) that defines radially inner and outer sides (R1, R2). The radially outer side (R2) includes radially-extending sidewalls (74) and a radially inner surface (76) that joins the radially-extending sidewalls, with the radially-extending sidewalls and the radially inner surface defining a pocket (78). A rail shield (80) has radially-extending walls (82) that line the radially-extending sidewalls. A spring (83) is configured to bias the rail shield radially inward.