Bleed Air Relief System Cover for Engine Cooling
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Solution Overview
Problem
Conventional bleed air relief systems in aircraft engines are inadequate in reducing the high temperature of bleed air injected into the bypass duct, leading to potential damage and failure of engine components due to prolonged exposure, especially when the bleed valve is in a failed open state.
Innovation Solution
A bleed air relief system that includes a diffuser nozzle and a cover with perforations over the outlet of the bleed air duct, creating a shear layer to enhance mixing of bleed air with bypass air, reducing its temperature through turbulence and heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional perforated cover is used to mix bleed air with bypass air, then some cooling effect is achieved, but the temperature reduction is limited under high pressure and high velocity flow conditions
Solution Approach 1:
The cover is segmented into multiple flow passages with different orientations (first set at first orientation, second set at second orientation). This segmentation creates multiple mixing zones that enhance turbulence and heat transfer, achieving more effective temperature reduction compared to a single conventional perforated cover design.
Solution Approach 2:
Different portions of the cover provide different flow control characteristics. The first set of flow passages and second set of flow passages are oriented differently to create localized mixing zones with varying turbulence intensities, optimizing cooling in different regions of the bypass duct.
2Temperature
If the bleed valve is in a failed open state, then continuous high pressure bleed air is injected into the bypass duct, but conventional covers cannot sufficiently reduce the temperature
Solution Approach 1:
The system dynamically adapts to failed open valve conditions through its multi-orientation flow passage design. The combination of differently oriented flow passages creates enhanced turbulence and mixing that dynamically responds to high velocity flow conditions, achieving effective cooling even when the valve remains continuously open.
Solution Approach 2:
The cover acts as an intermediary device between the high temperature bleed air source and the vulnerable engine components. By introducing multiple flow passages with different orientations, it creates intermediate mixing zones that progressively cool the bleed air before it reaches components like cascades and translating sleeves.
3Temperature
If high temperature bleed air is continuously injected into the bypass duct, then component damage occurs, but adding complex mixing structures increases device complexity
Solution Approach 1:
The cover serves multiple functions: it distributes bleed air through multiple flow passages, creates turbulence for mixing, directs flow in different orientations, and protects downstream components. This multi-functionality is achieved within a single integrated component rather than requiring multiple separate devices.
Solution Approach 2:
The cover incorporates a porous or perforated structure with multiple flow passages of different orientations. This porous design enables effective mixing and cooling through the walls of the bypass duct while maintaining a relatively simple overall structure that does not require complex external components.
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 reduces the temperature of bleed air impinging on engine components by up to 50°F, minimizing damage and extending the lifespan of components like cascades and translating sleeves.
Implementation Method 1
A diffuser is located ahead of the cover exit in a position to control the flow of bleed air. As the flow of bleed air passes through the flow passages and merges with the air exiting the diffuser, a shear layer is created between the flow passage and the diffuser nozzle.
Implementation Method 2
the velocity of at least a portion of the bleed air passing through the upper surface of the cover is changed to enhance mixing of the bleed air with the bypass air and accordingly reduce the temperature of the bleed air
Implementation Method 3
induce mixing of the bleed air with the bypass air for cooling of the bleed air prior to it impinging upon the walls of the bypass duct
Data Source
AI summary
A bleed air relief system for engines in which a flow of bleed air from the engine compressor is passed along a bleed air duct and exhausted into a bypass air stream passing through the engine. A cover is mounted over the outlet of the bleed air duct and can include flow passages and a diffuser for controlling the flow of bleed air being exhausted to enhance mixing of the bleed air with the bypass air stream.