Axial-Centrifugal Compressor Bleed for Combustor Start Airflow
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Solution Overview
Problem
Gas turbine engines with high-pressure compressors face challenges in providing sufficient compressed airflow to the combustor during start or restart conditions due to front-to-rear stage off-design mismatching, leading to potential stall and choked conditions.
Innovation Solution
A gas turbine engine design incorporating an axial-centrifugal compressor with a surge bleed plenum, a secondary airflow duct, and a valve that allows for controlled communication between the surge bleed plenum and the combustor inlet to bypass compressed air directly to the combustor, enhancing airflow during start or restart.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the overall cycle pressure ratio is increased to improve engine performance, then engine performance is improved, but the compressed airflow to the combustor during start operation decreases
Solution Approach 1:
The compressor airflow path is segmented into two separate paths: the main compression path through the axial-centrifugal compressor, and a bypass path through the surge bleed plenum and secondary airflow duct. This segmentation allows independent control of airflow to the combustor during starting conditions, resolving the contradiction by providing sufficient compressed airflow through the bypass path while maintaining high overall pressure ratio for performance.
Solution Approach 2:
The surge bleed plenum acts as an intermediary storage chamber that accumulates compressed air from the axial compressor outlet. During starting conditions, this intermediary plenum supplies compressed airflow to the combustor through the secondary airflow duct, bypassing the centrifugal compressor. This mediator resolves the contradiction by decoupling the high pressure ratio requirement from the combustor airflow requirement during start operation.
2Use of energy by moving object
If the high-pressure compressor operates at low speeds during starting conditions, then the compressor consumes less energy, but the front stages operate near stall conditions and rear stages operate in choked conditions, resulting in insufficient compressed airflow to the combustor
Solution Approach 1:
The axial compressor continuously compresses air and stores it in the surge bleed plenum during engine operation. During starting conditions, this pre-stored compressed air is readily available through the secondary airflow duct, eliminating the need for the centrifugal compressor to operate at high speeds. This preliminary action resolves the contradiction by providing sufficient compressed airflow without requiring high compressor speeds.
3Quantity of substance
If a bypass system is added to provide additional compressed airflow to the combustor, then compressed airflow to the combustor is increased, but the device complexity increases
Solution Approach 1:
The surge bleed plenum, originally designed for surge control in axial compressors, is given a dual function: it continues to protect against surge while also serving as a storage chamber for bypass airflow to the combustor during starting conditions. The secondary airflow duct and valve assembly are integrated into the existing compressor structure. This multi-functionality resolves the contradiction by providing additional compressed airflow capability without proportionally increasing system complexity.
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 ensures increased compressed airflow to the combustor, improving engine starting and restart capabilities by bypassing the centrifugal compressor, thus ensuring sustained combustion.
Implementation Method 1
The axial compressor has an axial compressor inlet and an axial compressor outlet
Implementation Method 2
the centrifugal compressor has a centrifugal compressor inlet and a centrifugal compressor outlet
Implementation Method 3
The valve is mounted on the secondary airflow duct and is movable between a closed position, in which the secondary airflow duct does not provide fluid communication between the surge bleed plenum and the combustor air inlet, and at least one open position, in which the secondary airflow duct provides fluid communication between the surge bleed plenum and the combustor air inlet
Implementation Method 4
the centrifugal compressor has a centrifugal compressor inlet and a centrifugal compressor outlet
Data Source
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AI summary
A gas turbine engine includes a combustor having a combustor air inlet, an axial-centrifugal compressor, a shroud, a secondary flow duct, and a valve. The shroud surrounds at least a portion of the axial-centrifugal compressor and has a surge bleed plenum defined therein that is in fluid communication with, and receives compressed air from, the axial compressor outlet. The secondary airflow duct has a duct inlet that is in fluid communication with the surge bleed plenum, and a duct outlet that is in fluid communication with the combustor air inlet. The valve is mounted on the secondary airflow duct and is movable between a closed position, in which the secondary airflow duct does not provide fluid communication between the surge bleed plenum and the combustor air inlet, and an open position, in which the secondary airflow duct provides fluid communication between the surge bleed plenum and the combustor air inlet.