Gas Turbine Exhaust Nozzle Strut Bracket Stiffness

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Solution Overview

Problem

The existing variable area exhaust nozzle of gas turbine engines faces thermal stresses due to different thermal expansion of the centerbody and struts exposed to hot core and bypass airflow, leading to structural challenges.

Innovation Solution

The exhaust nozzle incorporates a coupling arrangement with at least three brackets per strut, oriented to provide high stiffness in axial and circumferential directions while allowing low stiffness in radial directions, enabling radial movement to compensate for thermal expansion while hindering axial or circumferential displacement and reacting torsional moments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the centerbody and struts are rigidly connected to the nozzle wall, then structural stability is improved, but thermal stresses increase due to restricted thermal expansion

Engineering Contradiction:

Improvestructural stabilityVSAvoidthermal stresses

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The coupling arrangement is segmented into multiple brackets (at least three) that are spaced in the axial direction, allowing the connection to be divided into discrete segments that can independently accommodate thermal deformation while maintaining overall structural stability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The brackets are designed with direction-dependent stiffness parameters, having high stiffness in axial and circumferential directions to maintain stability, but low stiffness in radial direction to allow thermal expansion, thus changing the mechanical parameters to resolve the contradiction

Inventive Principle:

Principle #35Parameter changes

2Strength

If the brackets are made stiff in all directions, then structural integrity is improved, but thermal expansion compensation is hindered

Engineering Contradiction:

Improvestructural integrityVSAvoidthermal expansion compensation

Core Design Contradiction:

StrengthVSAdaptability or versatility

Solution Approach 1:

Each bracket is designed with non-uniform local quality, having different stiffness characteristics in different directions (high stiffness in axial and circumferential directions, low stiffness in radial direction), allowing the same component to simultaneously provide structural integrity and thermal expansion compensation

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The brackets are oriented asymmetrically with respect to the thermal expansion directions, with their highest stiffness direction aligned perpendicular to the dominant thermal expansion direction, enabling them to resist forces in certain directions while being forgiving in others

Inventive Principle:

Principle #4Asymmetry

3Stress or pressure

If multiple brackets are used to compensate thermal expansion, then thermal stress is reduced, but device complexity increases

Engineering Contradiction:

Improvethermal stressVSAvoiddevice complexity

Core Design Contradiction:

Stress or pressureVSDevice complexity

Solution Approach 1:

The brackets serve multiple functions simultaneously: they provide structural support, accommodate thermal expansion through controlled flexibility, resist torsional moments, and maintain axial positioning, thus reducing the need for separate components and lowering overall device complexity despite using multiple brackets

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Stability of the object's composition

If the brackets are oriented with high stiffness in radial direction, then radial stability is improved, but thermal expansion compensation is restricted

Engineering Contradiction:

Improveradial stabilityVSAvoidthermal expansion compensation

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The brackets are specifically oriented with their highest stiffness direction (first direction) aligned with the circumferential or axial direction, creating an asymmetric stiffness distribution that is intentionally non-uniform across different spatial directions, allowing radial movement while maintaining stability in other directions

Inventive Principle:

Principle #4Asymmetry

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 effectively compensates for thermal expansion of the centerbody and struts, reducing thermal stresses and maintaining structural integrity by allowing radial movement while constraining unwanted displacements and torsional moments.

Implementation Method 1

the centerbody and the struts are exposed both to the hot core airflow from the primary channel that has passed the core engine and to the colder bypass airflow from the bypass channel, whereas the outer nozzle wall is exposed mostly to the colder bypass airflow. This leads to a different thermal expansion of these components

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11326552B2Exhaust nozzle of a gas turbine engine

Publication Date: 2022.05.10 ROLLS ROYCE DEUT LTD & CO KG

AI summary

An exhaust nozzle of a gas turbine engine includes: a nozzle wall, a centerbody arranged in a flow channel, and two struts connecting the centerbody to the wall. One of the struts is connected to the wall by a coupling arrangement that includes two first brackets and a third bracket, the brackets being spaced in an axial direction and being connected either directly to the wall or to a sliding element that is arranged in a displaceable manner in the wall. The brackets each have a first, highest stiffness in a first direction and smaller stiffnesses in a second and third direction. The brackets are oriented such that with the two first brackets, the first direction is aligned with a circumferential direction of the nozzle and that with the third bracket, the first direction is aligned with the axial direction of the nozzle.