Aft Fan Counter-Rotating Engine Boundary Layer Ingestion

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Solution Overview

Problem

Conventional aircraft engines are oversized to counteract boundary layer drag, leading to decreased efficiency due to the resistance caused by the air boundary layer formed around the fuselage during flight.

Innovation Solution

An aft fan gas turbine engine configuration with a counter-rotating fan and turbine setup, where the aft fan ingests the boundary layer air, reducing drag and allowing the wing-mounted engines to be downsized, utilizing a gas generator that can operate as an auxiliary power unit and provide pressurized cooling air for active cooling of engine components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If engines are oversized to overcome boundary layer drag, then thrust requirement is met, but engine efficiency decreases

Engineering Contradiction:

ImprovethrustVSAvoidengine efficiency

Core Design Contradiction:

ForceVSUse of energy by moving object

Solution Approach 1:

The patent converts the harmful boundary layer drag into a beneficial force by using the aft fan to ingest the boundary layer air and redirect it to provide additional thrust. The boundary layer air, which previously resisted forward motion, is now utilized to enhance propulsion, thereby meeting thrust requirements without oversizing the engines and maintaining engine efficiency.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If conventional forward fan configuration is used, then engine structure is simple, but boundary layer drag cannot be effectively utilized

Engineering Contradiction:

Improveengine configurationVSAvoidboundary layer utilization

Core Design Contradiction:

Device complexityVSForce

Solution Approach 1:

The patent inverts the conventional engine configuration by placing the fan at the aft position instead of the forward position. This inversion allows the fan to ingest the boundary layer air that forms along the fuselage and redirect it to produce thrust, effectively utilizing the boundary layer drag that would otherwise be harmful. The counter-rotating twin fans further optimize this configuration.

Inventive Principle:

Principle #13The other way round (Inversion)

3Power

If wing-mounted engines are used, then thrust generation is effective, but they must be oversized to compensate for boundary layer resistance

Engineering Contradiction:

Improvethrust generationVSAvoidengine size

Core Design Contradiction:

PowerVSWeight of moving object

Solution Approach 1:

The patent merges the function of boundary layer management with thrust generation by integrating the aft fan system with the wing-mounted engines. The aft fan ingests boundary layer air and redirects it to augment thrust, allowing the wing-mounted engines to be downsized while maintaining effective thrust generation. This combination reduces the overall engine size and weight while preserving propulsion effectiveness.

Inventive Principle:

Principle #5Merging (Combining)

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 aft fan engine reduces thrust requirements by up to 15%, enabling wing-mounted engines to be downsized by 85%, and provides efficient power extraction and cooling, enhancing overall engine efficiency and reducing thermal stress on components.

Implementation Method 1

the aft fan is configured to ingest the boundary layer and redirect the air to provide additional thrust

Methodology Applied

Scientific EffectBoundary layer ingestion: Boundary Layer

Implementation Method 2

reducing drag and allowing the wing-mounted engines to be downsized

Methodology Applied

Scientific EffectDrag reduction: Drag

Implementation Method 3

An aft fan gas turbine engine configuration with a counter-rotating fan and turbine setup

Methodology Applied

Scientific EffectCounter-rotation:

Implementation Method 4

provides pressurized cooling air for active cooling of engine components

Methodology Applied

Scientific EffectActive cooling: Cooling

Implementation Method 5

reducing thermal stress on components

Methodology Applied

Scientific EffectThermal stress reduction:

Implementation Method 6

the exhaust duct is at least partially defined by a rotating frame

Methodology Applied

Scientific EffectExhaust flow:

Data Source

PatentEP3415437B1Aft fan counter-rotating turbine engine

Publication Date: 2020.08.19 RTX CORP

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AI summary

An exemplary boundary layer ingestion engine (300) includes a gas generator (310), a turbine (320) fluidly connected to the gas generator (310), and a fan (330) mechanically linked to the turbine (320) via at least one shaft (340). The linkage is configured such that rotation of the turbine (320) is translated to the fan (330). The boundary layer ingestion engine (300) further includes an exhaust duct fluidly connected to an outlet of the turbine (320). The exhaust duct is positioned radially inward of the fan (330).