Aft Fuselage Profile for Boundary Layer Ingestion
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Solution Overview
Problem
Existing aircraft designs with aft-mounted engines face challenges in efficiently ingesting low-momentum boundary layer airflow due to non-uniform velocity and total pressure profiles caused by stabilizers and other aft-end structures, which hampers propulsive efficiency.
Innovation Solution
The design of a fuselage with specific surface profiles and shapes at the aft end, including convex and concave regions, is intended to uniformly distribute and ingest boundary layer airflow into the aft engine, reducing swirl distortion and enhancing propulsive efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a fan is positioned at the aft end of the fuselage to reenergize boundary layer airflow, then propulsive efficiency is improved, but the airflow ingested by the fan becomes non-uniform with swirl distortion due to stabilizer structures
Solution Approach 1:
The fuselage surface is designed with different curvature characteristics in different regions: a first region with positive curvature (convex) and a second region with negative curvature (concave). This local differentiation of surface geometry creates corresponding differences in boundary layer development, allowing the airflow to be shaped into a more uniform profile by the time it reaches the fan inlet, thereby resolving the contradiction between propulsive efficiency and airflow uniformity.
2Stability of the object's composition
If stabilizer structures are present at the aft end of the fuselage, then aircraft stability is improved, but swirl distortion and non-uniform velocity profile are generated in the boundary layer airflow
Solution Approach 1:
The fuselage surface geometry is designed to create a beneficial boundary layer profile in advance, before the airflow reaches the stabilizer structures. By having the first region with positive curvature followed by the second region with negative curvature, the boundary layer is shaped to compensate for the disruptive effect of the stabilizers, thereby reducing swirl distortion while maintaining stability.
Solution Approach 2:
The design changes the geometric parameters of the fuselage surface by defining specific curvature characteristics (positive curvature in the first region, negative curvature in the second region). These parameter changes in the fuselage geometry directly affect boundary layer development and airflow characteristics, allowing the system to maintain stability while reducing swirl distortion.
3Manufacturing precision
If the fuselage surface is designed with specific convex and concave regions, then boundary layer airflow uniformity is improved, but the complexity of the fuselage structure increases
Solution Approach 1:
Rather than redesigning the entire fuselage, the invention applies specific curvature characteristics only to local regions: a first region with positive curvature and a second region with negative curvature. This localized approach to geometric modification achieves boundary layer control and airflow uniformity without requiring complete redesign of the fuselage structure, thereby limiting the increase in structural complexity.
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 fuselage design effectively captures and accelerates boundary layer airflow, improving the propulsive efficiency of the aircraft by reducing drag and enhancing thrust, while minimizing vibration, noise, and wear on the fan blades.
Implementation Method 1
the airflow ingested by such a fan may not have a uniform velocity or total pressure profile along the circumferential and radial directions of the fan. More specifically, the structures at the aft end of the fuselage may generate a boundary layer or wake resulting in swirl distortion
Data Source
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AI summary
An aircraft is provided including a fuselage that extends along a longitudinal direction between a forward end and an aft end. A boundary layer ingestion fan is mounted to the fuselage at the aft end and is configured for ingesting boundary layer airflow off the surface of the fuselage. The fuselage defines a profile proximate the boundary layer ingestion fan that is optimized for ingesting a maximum amount of boundary layer air and improving propulsive efficiency of the aircraft. More specifically, the fuselage defines a cross sectional profile upstream of the boundary layer ingestion fan that has more cross sectional area in a top half relative to a bottom half as defined relative to a centerline of the boundary layer ingestion fan.