Aft Engine Air Injection for Uniform Boundary Layer Ingestion
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Solution Overview
Problem
Conventional aircraft designs with turbofan jet engines positioned beneath the wings face issues with drag and inconsistent airflow velocity profiles due to structures at the aft end of the fuselage, leading to swirl distortion and reduced propulsive thrust.
Innovation Solution
The integration of an aft engine mounted to the fuselage, equipped with a boundary layer ingestion system that includes an injection assembly to redirect and uniform airflow velocity, using supplemental airflow to improve the ingestion efficiency of low momentum air and reduce swirl distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an aft engine is positioned at the aft end of the fuselage to reenergize boundary layer airflow, then boundary layer airflow can be ingested, but the existing structures at the aft end generate wake resulting in swirl distortion and inconsistent velocity profile
Solution Approach 1:
A flow conditioning assembly is introduced as an intermediary component between the aft engine inlet and the fuselage structures. This assembly includes flow straightening vanes that condition the airflow by reducing swirl distortion and uniformizing the velocity profile before the air enters the engine, thereby mediating between the boundary layer ingestion requirement and the velocity consistency requirement
Solution Approach 2:
The flow conditioning assembly provides localized flow treatment at the engine inlet region. By placing flow straightening vanes specifically at the inlet, the solution addresses the local quality of airflow non-uniformity without altering the overall aft engine positioning or fuselage structures, enabling boundary layer ingestion while maintaining velocity profile consistency
2Reliability
If conventional turbofan jet engines are mounted beneath the wings separated from the wing and fuselage, then the engines can interact with separate freestream airflows reducing turbulence, but drag on the aircraft increases affecting net propulsive thrust
Solution Approach 1:
Instead of positioning engines beneath the wings to access freestream flow, the invention inverts the approach by positioning an aft engine at the rear of the fuselage to ingest boundary layer airflow. This inverted configuration allows the engine to directly utilize the slow-moving air already present at the fuselage surface, converting what is typically considered a harmful boundary layer into a useful resource for propulsion
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
Enhances propulsive efficiency by ensuring uniform airflow distribution to the aft engine, reducing drag and increasing net thrust while maintaining a desired takeoff angle.
Implementation Method 1
a fuselage of an aircraft designed to increase the ingestion of relatively low momentum boundary layer airflow into the aft engine
Implementation Method 2
an injection assembly to redirect and uniform airflow velocity, using supplemental airflow to improve the ingestion efficiency
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An air injection assembly for an aircraft is provided. The aircraft includes a fuselage extending between a forward end and an aft end along a longitudinal direction and a boundary layer ingestion fan mounted to the fuselage at the aft end of the fuselage. The air injection assembly includes at least one injection port defined on a surface of the fuselage at a location upstream of the boundary layer ingestion fan. A supplemental airflow is provided through a fluid passageway to the injection port where it is ejected to displace at least a portion of relatively higher velocity boundary layer airflow. In this manner, the airflow entering boundary layer ingestion fan is more uniform, has less swirl distortion, and has a lower average velocity.