Non-axis symmetric aft engine inlet for boundary layer ingestion
Solution Overview
Problem
Conventional aircraft propulsion systems face inefficiencies due to drag caused by turbofan jet engines, which can be exacerbated by the nonuniform velocity profile of boundary layer air ingestion, and existing solutions like boundary layer ingestion propulsors interfere with takeoff angles.
Innovation Solution
An aft engine is mounted to the fuselage near the rear of the aircraft, configured as a boundary layer ingestion engine with a frustoconical fuselage shape and a recessed portion to allow for efficient capture of boundary layer air without interfering with the takeoff angle, using a fan and nacelle design that directs and energizes this air to reduce drag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a boundary layer ingestion propulsor is added to the aircraft at the aft end, then drag is reduced by reenergizing the boundary layer airflow, but the takeoff angle of the aircraft is interfered with
Solution Approach 1:
The aft engine is designed with a non-axis symmetric inlet shape that is asymmetric with respect to the aircraft's longitudinal centerline. The inlet extends further below the longitudinal centerline than above it, allowing the engine to be positioned such that it ingests boundary layer air from the fuselage without interfering with the takeoff angle. This asymmetric configuration enables the engine to capture slow-moving boundary layer air while maintaining proper ground clearance during takeoff.
Solution Approach 2:
The inlet of the aft engine is configured to extend in multiple directions, particularly below the longitudinal centerline of the aircraft. This three-dimensional inlet configuration allows the engine to access boundary layer air that flows along the fuselage surface without requiring the engine to be positioned high enough to interfere with takeoff operations. The inlet captures air from various angular directions to achieve boundary layer ingestion while preserving takeoff geometry.
2Loss of energy
If boundary layer air is ingested into the turbofan jet engine, then drag is reduced, but the efficiency of the engine is reduced due to nonuniform velocity profile
Solution Approach 1:
The aft engine is specifically designed as a boundary layer ingestion engine with localized inlet positioning and shaping optimized for capturing boundary layer air. The non-axis symmetric inlet configuration is tailored to match the local boundary layer flow patterns around the fuselage, allowing efficient ingestion of slow-moving air without compromising overall engine performance. The engine's inlet geometry is locally optimized to accommodate the distorted velocity profile of boundary layer air.
3Reliability
If turbofan jet engines are mounted beneath the wings, then they can interact with separate freestream airflows, but drag on the aircraft increases
Solution Approach 1:
The aft engine merges the boundary layer air that flows along the fuselage surface with the freestream air. By positioning the engine at the rear of the fuselage with an inlet that captures boundary layer air, the design combines the previously separate airflow paths (boundary layer and freestream) into a unified propulsion system. This merging allows the engine to utilize both air sources, reducing drag while maintaining adequate airflow quality 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
This configuration enhances propulsive efficiency by reducing drag and maintaining the aircraft's takeoff angle, effectively capturing and energizing boundary layer air to improve net thrust without interference.
Implementation Method 1
boundary layer air forming a boundary layer across the fuselage of the aircraft
Implementation Method 2
reduce drag by reenergizing the boundary layer airflow downstream from the aircraft
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An aircraft (10) including a fuselage (20) and an aft engine (200) is provided. The fuselage (20) extends from a forward end of the aircraft (10) towards an aft end (16) of the aircraft (10). The aft engine (200) is mounted to the fuselage (20) proximate the aft end (16) of the aircraft (10). The aft engine (200) includes a fan (222) rotatable about a central axis (220) of the aft engine (200), the fan (222) including a plurality of fan blades (228). The aft engine (200) also includes a nacelle (224) surrounding the plurality of fan blades (228) and defining an inlet (244). The inlet (244) defines a non-axis symmetric shape with respect to the central axis (220) of the aft engine (200) to, e.g., allow for a maximum amount of airflow into the aft engine (200).