Variable Bleed Valve for Gas Turbine Booster Stall Prevention
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Solution Overview
Problem
Modern high bypass ratio gas turbine engines face difficulties in bleeding sufficient air from downstream of the booster to prevent stall and efficiently provide cooling air for thermal management systems, due to the reduced pressure difference between the booster exit and the fan bypass duct.
Innovation Solution
A gas turbine engine variable bleed apparatus featuring axially adjacent annular booster bleed plenums, a rotatable valve body with a variable bleed valve door, and a rotatable plenum door that controls flow through an inter plenum aperture, allowing for efficient bleeding of air and directing it through exhaust ducts to a bypass flow path, which includes heat exchangers for thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher pressure core compressors and lower pressure boosters are used to increase bypass ratio, then engine efficiency is improved, but the pressure difference between booster exit and fan bypass duct is reduced making it difficult to bleed sufficient air for stall prevention
Solution Approach 1:
The bleed valve is divided into multiple independently controllable doors (first bleed door, second bleed door, third bleed door) that can be operated separately to regulate air flow through different passages, enabling precise control of bleed air quantity despite reduced pressure differential
Solution Approach 2:
The bleed valve incorporates variable geometry with movable doors that can dynamically adjust opening positions based on operating conditions, allowing the system to adapt to varying pressure differences and maintain sufficient bleed air flow for stall prevention across different engine operating points
2Temperature
If more air is bled from the booster for thermal management, then cooling capability is improved, but the pressure difference available for bleeding is reduced in high bypass ratio engines
Solution Approach 1:
The system provides different bleed air flows to different locations (fan bypass duct for stall prevention, thermal management system for cooling) through separate controllable passages and doors, allowing optimized air distribution based on local requirements despite limited overall pressure availability
Solution Approach 2:
The variable bleed valve dynamically adjusts door positions and opening areas to modulate bleed air flow parameters, enabling the system to extract sufficient cooling air for thermal management while maintaining adequate pressure differential for booster stall prevention
3Device complexity
If conventional single door bleed valves are used, then device complexity is low, but sufficient air bleeding for both stall prevention and thermal management cannot be achieved
Solution Approach 1:
The bleed valve is divided into multiple independently controllable doors (first bleed door, second bleed door, third bleed door) that can be operated separately to regulate air flow through different passages, enabling precise control of bleed air quantity despite reduced pressure differential
Solution Approach 2:
The multi-door bleed valve structure serves multiple functions simultaneously: preventing booster stall through controlled bleeding to the fan bypass duct and providing cooling air to the thermal management system, making a single device capable of addressing both requirements that a conventional single door valve cannot satisfy
Data Source
AI summary
Axially adjacent annular booster bleed aft and forward plenums with annular common wall therebetween extend radially outwardly from transition duct. Variable bleed valve includes bleed valve door in bleed inlet in transition duct, attached to rotatable valve body rotatable about axis of rotation, operable to open and close bleed inlet to aft plenum. Rotatable plenum door clocked or circumferentially spaced apart from variable bleed valve door and attached to rotatable valve body, operable to close and open up and control flow through an inter plenum aperture in common wall. Aft and forward bleed exhaust ducts extend from booster bleed aft and forward plenums to bypass flow path. One or more heat exchanger, such as from thermal management system, may be disposed in the bleed exhaust ducts. Heat exchangers may be used for cooling oil for power gear box and/or engine bearings, air conditioning, or variable frequency generator.