Gas Turbine Aft Hub Sealing System for Windage Heating Reduction
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Solution Overview
Problem
Gas turbine engines face issues with windage heating and oil degradation due to heated compressed air entering the oil sump, leading to power loss and seal degradation.
Innovation Solution
An aft hub sealing assembly comprising an aft baffle, bearing cap with multiple seals, and an air shield, which reduces temperature and pressure within the bearing assembly by preventing compressed gas from entering the oil sump through a combination of brush and labyrinth seals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If compressed air is redirected along secondary paths to cool combustor and turbine sections, then cooling effectiveness is improved, but windage heating increases and leads to oil degradation
Solution Approach 1:
The bearing assembly is divided into multiple sealed compartments using bearing caps and air shields. The first bearing cap creates a first sealed compartment, while the second bearing cap and air shield create a second sealed compartment. This segmentation prevents heated compressed air from mixing with the oil sump, thereby reducing windage heating's harmful effects on oil while maintaining cooling effectiveness.
Solution Approach 2:
Air shields act as intermediary barriers between the compressed air paths and the oil sump. The air shields prevent direct communication between the heated compressed air and the oil, serving as a mediator that allows the cooling system to function while protecting the oil from thermal degradation.
2Reliability
If multiple seals are used to prevent compressed gas from entering the oil sump, then oil degradation is reduced, but device complexity increases
Solution Approach 1:
The sealing system is segmented into multiple functional components: first seals in the first bearing cap, second seals in the second bearing cap, and air shields forming additional sealed compartments. This segmentation allows each seal to address specific leakage paths, improving overall reliability while distributing the sealing function across multiple manageable components.
Solution Approach 2:
The sealing structure employs a nested arrangement where air shields are positioned within the bearing assembly, and bearing caps enclose the seals. The air shields form inner sealed compartments while the bearing caps provide outer sealing, creating a nested protective structure that prevents compressed air from reaching the oil sump through multiple concentric barriers.
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 windage heating and prevents compressed gas from entering the oil sump, thereby minimizing power loss and seal degradation, enhancing the operational efficiency and longevity of gas turbine engines.
Implementation Method 1
The device has a shaft carried in a housing on bearings with a compressor wheel on one side and an expander wheel on the other side. Labyrinth seals seal the wheels from the interior of the housing and the bearings.
Implementation Method 2
Mechanical seals are located between the bearings and the labyrinth seals for preventing leakage of oil.
Implementation Method 3
Gas is injected from the compressor discharge into a groove on the expander side of the shaft to provide a thermal barrier.
Implementation Method 4
The O-ring is located in a groove in the bore and a recess formed in the nonrotating ring. The recess is offset to deform the ring and cause it to exert a force on the nonrotating ring against the rotating ring.
Data Source
AI summary
An aft hub sealing assembly for a gas turbine engine is disclosed. The aft hub sealing assembly includes an aft hub, a bearing cap, an aft baffle, a first seal, and a second seal. The aft hub includes a body portion and a disk portion aft surface. The bearing cap includes a bearing cap inner portion spaced apart from the body portion. The aft baffle is located adjacent the disk portion. The aft baffle includes a baffle forward surface following a contour of the disk portion aft surface. The first seal is between the bearing cap inner portion and the body portion. The second seal is between the bearing cap inner portion and the body portion.