Boundary Layer Guide Walls for Embedded Engine Drag Reduction

Solution Overview

Problem

Civil airplanes with partially embedded turbojet engines face challenges in reducing aerodynamic drag, which affects fuel consumption and engine efficiency due to the ingestion of the boundary layer.

Innovation Solution

The use of boundary layer guide walls extending upstream from the air intake of the engine, flaring apart and converging to form a half-chute, combined with an S-shaped fuselage profile, to maximize boundary layer absorption and reduce drag, while ensuring efficient air guidance and thermal protection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If engines are partially embedded in the fuselage to reduce drag and eliminate pylons, then weight is reduced and fuel consumption decreases, but the boundary layer is ingested by the engines causing fan distortion and shaft vibration

Engineering Contradiction:

Improveweight of propulsion assemblyVSAvoidengine stability

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The air intake is segmented into two distinct zones: an upper zone that ingests high-quality free stream air and a lower zone that ingests boundary layer air. This segmentation allows the engine to selectively process different air qualities, maintaining fan stability while still benefiting from boundary layer absorption for drag reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A diversion wall acts as an intermediary structure between the boundary layer and the fan. It redirects the low-speed boundary layer air away from the fan inlet, preventing direct ingestion that would cause distortion and vibration, while still allowing the boundary layer to be absorbed into the engine through controlled pathways.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If boundary layer traps are installed upstream from air intakes to prevent boundary layer ingestion, then engine stability is maintained, but aerodynamic drag is not sufficiently reduced

Engineering Contradiction:

Improveengine stabilityVSAvoidaerodynamic drag

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

Instead of using traditional boundary layer traps that block and redirect boundary layer air away from the engine, this invention inverts the approach by allowing boundary layer air to be directly ingested into the engine through a dedicated lower intake zone. This inversion converts the harmful boundary layer into a useful resource for drag reduction while maintaining engine stability through proper flow management.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The air intake system is designed with different velocity thresholds for its two zones. The upper intake targets higher velocity free stream air, while the lower intake captures lower velocity boundary layer air. This parameter-based differentiation optimizes both drag reduction and engine performance by matching air source characteristics to engine requirements.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the air intake is positioned to absorb more boundary layer, then aerodynamic drag is reduced and fuel consumption decreases, but fan distortion and shaft vibration increase

Engineering Contradiction:

Improveaerodynamic dragVSAvoidengine stability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The air intake is segmented into two distinct zones: an upper zone that ingests high-quality free stream air and a lower zone that ingests boundary layer air. This segmentation allows the engine to selectively process different air qualities, maintaining fan stability while still benefiting from boundary layer absorption for drag reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A diversion wall acts as an intermediary structure between the boundary layer and the fan. It redirects the low-speed boundary layer air away from the fan inlet, preventing direct ingestion that would cause distortion and vibration, while still allowing the boundary layer to be absorbed into the engine through controlled pathways.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces aerodynamic drag and increases engine efficiency by absorbing a greater portion of the boundary layer, leading to a 3% to 5% decrease in fuel consumption and improved engine performance.

Implementation Method 1

a boundary layer at substantially zero speed is formed around the fuselage of the airplane

Methodology Applied

Scientific EffectBoundary layer: Boundary Layer

Implementation Method 2

absorbing a portion of the boundary layer in the engines makes it possible significantly to reduce the aerodynamic drag of the airplane

Methodology Applied

Scientific EffectDrag reduction through boundary layer absorption: Drag

Implementation Method 3

the portion of the fuselage situated between the two guide walls has an S-shaped profile with a concave side towards the air intake of the engine, thus enabling the air to be accelerated between the two guide walls, and enabling the air suction effect to be increased

Methodology Applied

Scientific EffectAir suction effect: Suction

Data Source

PatentUS8684302B2Airplane having engines partially encased in the fuselage

Publication Date: 2014.04.01 SAFRAN AIRCRAFT ENGINES SAS

AI summary

An airplane provided with dual-flow turbojet engines having nacelles at least partially encased in the fuselage, wherein the air intake of each engine is connected to the fuselage by two boundary layer guiding walls, the walls extending towards the upstream side of the air intake and being spaced apart towards the upstream side.