Aircraft Nacelle Secondary Flow Path Angular Offset

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Solution Overview

Problem

The existing aircraft propulsion units face challenges in maintaining effective sealing and aerodynamic alignment between the turbojet engine and the nacelle due to torsional deformations caused by fan twist, leading to leakage and reduced aerodynamic qualities of the secondary flow path.

Innovation Solution

Introducing an initial angular offset between the secondary flow path portions defined by the engine and the nacelle when the engine is stopped, allowing for improved alignment during operation, and using a gasket with high crushing amplitude to manage relative movements and deformations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the nacelle structure is rigidly aligned with the engine when stopped, then manufacturing and assembly are simplified, but aerodynamic alignment deteriorates during operation due to fan twist

Engineering Contradiction:

Improvealignment simplicityVSAvoidaerodynamic alignment precision

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The nacelle structure is pre-aligned at an angle relative to the engine when the engine is in the stopped state, rather than being perfectly aligned. This preliminary angular offset compensates for the fan twist that occurs during operation, ensuring that the secondary flow path remains aerodynamically aligned when the engine is running.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If a gasket with high crushing amplitude is used to accommodate relative movements, then sealing reliability improves, but gasket weight and cost increase

Engineering Contradiction:

Improvesealing reliabilityVSAvoidgasket weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The gasket is designed with specific material parameters and geometric characteristics that allow it to accommodate the relative movements between the nacelle and engine while maintaining effective sealing. The gasket's crushing amplitude is optimized to match the expected displacement range, avoiding excessive material usage while ensuring sealing reliability throughout the operational envelope.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the secondary flow path is sealed with high precision, then aerodynamic losses are reduced, but the system becomes sensitive to relative movements and deformations

Engineering Contradiction:

Improveaerodynamic lossesVSAvoidtolerance to relative movement

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The gasket serves as an intermediary element between the nacelle structure and the engine, providing a compliant sealing interface that accommodates relative movements and deformations. This intermediary allows the system to maintain aerodynamic alignment and sealing effectiveness despite the dynamic conditions during engine operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9963999B2Aircraft propulsion assembly

Publication Date: 2018.05.08 SAFRAN NACELLES

AI summary

The disclosure relates to an aircraft propulsion assembly comprising a bypass turbojet engine equipped with a nacelle, the bypass turbojet engine including a structure defining a first part of a secondary flow path for channeling secondary flow, and the nacelle having a structure defining a second part of the secondary flow path. The structure of the nacelle defining the second part of the secondary flow path is arranged such that the first part and the second part of the secondary flow path are angularly offset around a longitudinal axis of the engine when the engine is shut down/stopped.