Aft Fuselage Boundary Layer Ingestion Fan Design
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Solution Overview
Problem
Conventional aircraft configurations with turbofan jet engines mounted under the wings face challenges in propulsive efficiency due to drag, and positioning a fan at the aft end of the fuselage can interfere with takeoff and landing capabilities.
Innovation Solution
An aircraft design featuring a boundary layer ingestion fan positioned within the fuselage at the aft end, with a circumferentially extending inlet and exhaust, allowing for the ingestion and re-energization of slow-moving boundary layer airflow without compromising takeoff or landing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fan is positioned at the aft end of the fuselage to reenergize boundary layer airflow, then propulsive efficiency is improved, but the aircraft's ability to take-off or land is negatively affected
Solution Approach 1:
The inlet is designed with nonuniform geometry where the lower half inlet area is greater than the upper half inlet area. This local differentiation allows the inlet to preferentially capture slow-moving boundary layer airflow from the lower fuselage regions while maintaining appropriate take-off and landing geometry.
Solution Approach 2:
The boundary layer ingestion fan is positioned within the fuselage at the aft end, creating a dynamic system that can ingest and reenergize boundary layer airflow during cruise flight to improve propulsive efficiency, while the inlet geometry is designed to prevent interference with take-off and landing operations.
2Object-affected harmful factors
If turbofan jet engines are mounted under the wings separated from the fuselage, then turbulence in the air entering the engine inlet is reduced, but drag on the aircraft increases
Solution Approach 1:
The patent converts the harmful drag effect into a benefit by designing the fuselage inlet to capture the slow-moving boundary layer airflow that is created by the fuselage itself. This boundary layer airflow, which would normally represent energy loss, is reenergized by the fan to improve overall propulsive efficiency.
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
This design enhances propulsive efficiency by re-energizing boundary layer airflow while maintaining the aircraft's ability to take off and land without interference, improving net propulsive thrust and reducing drag-related inefficiencies.
Implementation Method 1
Positioning a fan at an aft end of the fuselage of the aircraft may assist with reenergizing a boundary layer airflow over the aft end of the fuselage
Implementation Method 2
A total amount of drag on the aircraft, including skin friction and form drag, is generally proportional to a difference between a freestream velocity of air approaching the aircraft and an average velocity of a wake downstream from the aircraft
Data Source
AI summary
An aircraft includes a boundary layer ingestion fan defining a centerline and including a plurality of fan blades rotatable about the centerline. The aircraft also includes a fuselage extending between a forward end and an aft end along a longitudinal direction, the boundary layer ingestion fan positioned within the fuselage at the aft end of the fuselage, the fuselage defining an inlet upstream of the boundary layer ingestion fan extending at least about 180 degrees around the centerline of the boundary layer ingestion fan, the fuselage further defining an exhaust downstream of the boundary layer ingestion fan.