Exhaust Eductor Baffle for APU Cooling Recirculation
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Solution Overview
Problem
Conventional exhaust eductor systems for aircraft auxiliary power units face inefficiencies due to turbulent mixed flow streams recirculating back into the APU compartment, leading to inadequate cooling, especially when the active flow stream is at an angle relative to the mixing duct, resulting in high temperatures and potential system failure.
Innovation Solution
Incorporating a baffle within the mixing duct to prevent recirculation of the mixed flow streams, which is angled and positioned to divert the mixed flow back into the duct, thereby enhancing the cooling efficiency by ensuring the active and passive flow streams mix effectively without recirculating into the APU compartment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the active flow stream is at an angle relative to the mixing duct, then the exhaust eductor system can handle angled flow paths, but the mixed flow streams become turbulent and recirculate back into the APU compartment causing inadequate cooling
Solution Approach 1:
The mixing duct is divided into multiple sections with internal baffles that segment the flow path. These baffles create distinct flow zones that prevent turbulent mixing and recirculation, while still allowing the duct to accommodate angled active flow streams from the exhaust nozzle.
Solution Approach 2:
Internal baffles are introduced as intermediary elements within the mixing duct. These baffles act as flow control mechanisms that mediate between the angled active flow stream and the passive flow stream, preventing direct turbulent mixing and recirculation back into the APU compartment.
2Reliability
If cooling fans are used to cool the APU oil and engine externals, then cooling effectiveness is improved, but costs, weight, and noise levels increase
Solution Approach 1:
The patent replaces the mechanical cooling fan system with an exhaust eductor system that uses fluid dynamic principles. The eductor utilizes the kinetic energy of the exhaust stream to create a low-pressure zone that draws in cooling air, eliminating the need for separate mechanical cooling fans and reducing overall system weight.
Solution Approach 2:
The system employs pneumatic principles by using the exhaust flow to create pressure differential that drives the cooling air intake. The eductor design utilizes fluid dynamics to move cooling air through the mixing duct without mechanical pumps or fans, reducing weight while maintaining cooling effectiveness.
3Reliability
If cooling fans are used to cool the APU oil and engine externals, then cooling effectiveness is improved, but costs and noise levels increase
Solution Approach 1:
The patent replaces the mechanical cooling fan system with an exhaust eductor system that uses fluid dynamic principles. The eductor utilizes the kinetic energy of the exhaust stream to create a low-pressure zone that draws in cooling air, eliminating the need for separate mechanical cooling fans and reducing overall system weight.
Solution Approach 2:
The system employs pneumatic principles by using the exhaust flow to create pressure differential that drives the cooling air intake. The eductor design utilizes fluid dynamics to move cooling air through the mixing duct without mechanical pumps or fans, reducing weight while maintaining cooling effectiveness.
4Device complexity
If the mixed flow streams recirculate back into the APU compartment, then the exhaust eductor system can maintain simpler duct geometry, but cooling efficiency decreases and system failure can occur
Solution Approach 1:
The mixing duct is divided into multiple sections with internal baffles that segment the flow path. These baffles create distinct flow zones that prevent turbulent mixing and recirculation, while still allowing the duct to accommodate angled active flow streams from the exhaust nozzle.
Solution Approach 2:
The baffles extend into the flow path, adding a dimensional element that disrupts recirculation patterns. By introducing this third dimension (depth into the flow), the system prevents recirculation without significantly complicating the overall duct geometry.
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 baffle effectively reduces temperatures within the APU compartment from 400-700°F to 170-200°F, improving cooling efficiency and preventing system failures by preventing recirculation of mixed flow streams, thus enhancing the reliability and performance of the exhaust eductor system.
Implementation Method 1
A mixing duct at least partially surrounds the primary exhaust nozzle and transports a passive flow stream that is entrained by mixing with the active flow stream from the primary exhaust nozzle
Implementation Method 2
a baffle is on the interior of the mixing duct and configured to prevent the mixed flow streams from exiting the mixing duct back into the APU compartment
Implementation Method 3
The entrained passive flow stream flows through and cools the APU
Data Source
AI summary
An exhaust eductor system includes a primary exhaust nozzle configured to transport an active flow stream; and a mixing duct at least partially surrounding the primary exhaust nozzle and configured to transport a passive flow stream that is entrained by mixing with the active flow stream from the primary exhaust nozzle. The mixing duct has an interior, and a baffle on the interior of the mixing duct is configured to prevent the mixed flow streams from exiting the mixing duct.