Variable-Geometry Boundary Layer Diverter for Gas Turbine Inlets

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Solution Overview

Problem

The ingestion of a wide fuselage boundary layer into gas turbine engines can lead to operational challenges and fan blade stress, particularly during conditions like top of descent where fan speed is reduced and inlet airflow decreases, despite high aircraft velocity.

Innovation Solution

A selectively moveable bypass door system is positioned forward of the engine inlet, allowing boundary layer air to be bypassed around the engines during specific flight conditions, such as descent, by pivoting and creating a gap for air to pass beneath the engine, thereby reducing stress on the fan rotor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the boundary layer is ingested into the engine during descent with reduced fan speed, then propulsive efficiency is improved, but fan blade stress and operational reliability deteriorate

Engineering Contradiction:

Improvepropulsive efficiencyVSAvoidengine operability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The bypass door is designed to be dynamically adjustable, transitioning between a closed position (allowing boundary layer ingestion for efficiency) and an open position (bypassing boundary layer for safety). The system adapts its configuration based on real-time flight conditions, particularly fan speed and boundary layer thickness, resolving the contradiction between efficiency and reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the flow path parameter by moving the bypass door between positions. This parameter change allows the engine to switch between two operational modes: boundary layer ingestion mode (door closed) for efficiency and boundary layer bypass mode (door open) for reliability, depending on the operating conditions.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If the boundary layer is ingested during high velocity descent, then fuel burn performance is improved, but fan blade stress increases

Engineering Contradiction:

Improvefuel burn performanceVSAvoidfan blade stress

Core Design Contradiction:

Loss of energyVSStress or pressure

Solution Approach 1:

The bypass door acts as an intermediary mechanism that mediates between the boundary layer flow and the engine inlet. By controlling the door position, the system can selectively allow or block boundary layer ingestion, thus mediating between the benefits of fuel efficiency and the risks of fan blade stress.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If a fixed geometry inlet is used, then device complexity is reduced, but adaptability to varying flight conditions deteriorates

Engineering Contradiction:

Improveinlet structure complexityVSAvoidadaptability to flight conditions

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The inlet structure incorporates a movable bypass door that transitions between fixed positions, adding minimal complexity while enabling significant adaptability. The door can be positioned to accommodate different flight conditions (climb, cruise, descent, idle), making the inlet versatile without requiring complete geometric reconfiguration.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentEP3392150B1Variable-geometry boundary layer diverter

Publication Date: 2022.08.24 RTX CORP

Figure 1A~1B
Figure 2A~3

AI summary

A gas turbine engine (24) comprises a housing having an inlet leading to a fan rotor (42). A bypass door (28) is mounted upstream of the inlet to the fan rotor (42), and is moveable away from a non-bypass position to a bypass position to selectively bypass boundary layer air vertically beneath (38) the engine (24). An aircraft (20) is also disclosed.