Bleed Ejector FOD Expulsion in Gas Turbine Compressors
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Solution Overview
Problem
Gas turbine engines face challenges in expelling Foreign Object Debris (FOD) due to insufficient pressure ratios between the compressor and bypass duct, leading to potential FOD accumulation and flow reversal.
Innovation Solution
A bleed valve system with a duct, valve member, and ejector is implemented, where the valve member diverts fluid flow to create a vena contracta and the ejector supplies additional fluid to accelerate the flow, increasing the pressure ratio and preventing FOD from returning to the compressor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the compressor rotational speed decreases, then the power consumption and mechanical stress are reduced, but the static pressure in the compressor decreases leading to insufficient pressure ratio for FOD expulsion
Solution Approach 1:
An ejector is introduced as an intermediary device that uses a motive fluid (bled air or external source) to accelerate the main flow through a nozzle, creating a low-pressure region that enhances FOD expulsion capability without requiring high compressor rotational speed. The ejector acts as a mediator between the available pressure and the required expulsion force.
Solution Approach 2:
The system changes the flow parameters by introducing a motive fluid that accelerates the main flow, transforming the pressure ratio mechanism from relying solely on compressor speed to utilizing jet acceleration effects. This parameter change allows effective FOD expulsion at lower compressor speeds.
2Loss of energy
If the pressure ratio between compressor and bypass duct is insufficient, then energy loss is reduced, but FOD accumulates within the compressor and flow reversal occurs
Solution Approach 1:
The ejector utilizes pneumatic principles by introducing a motive fluid that creates a jet flow through a nozzle. This jet flow generates a low-pressure region that entrains and accelerates the main flow, providing sufficient force to expel FOD without requiring a large static pressure difference between compressor and bypass duct.
Solution Approach 2:
The system changes from relying on static pressure difference to utilizing dynamic pressure through jet acceleration. The motive fluid transforms the energy form, allowing effective FOD expulsion with minimal energy loss while preventing FOD accumulation.
3Device complexity
If a traditional bleed system is used without ejector, then the device complexity is low, but the FOD expulsion reliability is insufficient under certain operating conditions
Solution Approach 1:
The ejector is introduced as a relatively simple intermediary component that consists of a nozzle and mixing section. It mediates between the available bled air pressure and the required FOD expulsion force, significantly improving reliability without adding substantial complexity to the bleed system.
Solution Approach 2:
The ejector introduces dynamic flow characteristics through jet acceleration and flow entrainment. This dynamic mechanism allows the system to adapt to varying operating conditions and maintain effective FOD expulsion across a wider range of compressor speeds and pressure ratios.
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 system effectively expels FOD from the compressor by increasing the pressure ratio, ensuring that FOD is directed out of the system and preventing flow reversal, thus enhancing the safety and efficiency of gas turbine engines.
Implementation Method 1
According to Bernoulli's principle, as the speed of a flow increases, the static pressure of the flow decreases. Therefore, by supplying the additional flow of fluid, the part of the main flow of fluid diverted by the valve member accelerates downstream of the valve member and its static pressure decreases.
Implementation Method 2
The valve member may divert at least a part of the main flow of fluid to create a vena contract in that part of the main flow downstream of the valve member.
Data Source
AI summary
A bleed valve system comprises a duct, featuring a central longitudinal axis and allowing a main flow of fluid to pass from a first environment at a first static pressure to a second environment at a second static pressure along a bleed direction, a valve comprising a valve member arranged within the duct between the first and second environments and movable to partially obstruct the duct and deviate the main flow of fluid to direct at least a part of it towards a portion of an internal wall of the duct; and an ejector, arranged within the duct, downstream of the valve member and offset from the central longitudinal axis in correspondence of said portion of the internal wall, adapted to supply an additional flow of fluid within the duct to accelerate the main flow of fluid and reduce the second static pressure.