Segmented Turbine Exhaust Case Thermal Expansion

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Solution Overview

Problem

The existing sheet metal turbine exhaust cases face challenges in thermal and structural mismatch, leading to potential deformation due to thermal growth of struts, which limits the choice of materials and construction methods, especially in achieving balanced stiffness between the outer and inner shrouds while maintaining lightweight design.

Innovation Solution

A turbine exhaust case design featuring a segmented inner shroud with arcuate panels and circumferentially spaced-apart struts that allow for thermal expansion and contraction, along with a unitary outer shroud of different stiffness, connected by struts that also serve as acoustic panels for sound attenuation, addressing thermal mismatch and stress relief.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the inner and outer shrouds are made of the same sheet metal material to maintain balanced stiffness, then structural compatibility is improved, but the ability to accommodate thermal expansion of struts deteriorates

Engineering Contradiction:

Improvestiffness balanceVSAvoidthermal expansion accommodation

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The inner shroud is divided into multiple circumferentially spaced-apart arcuate panels that can move relative to each other, allowing differential thermal expansion while maintaining overall structural integrity. This segmentation enables the shroud to accommodate strut thermal growth without requiring the entire structure to expand uniformly.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inner shroud panels are designed to be movable relative to one another, transforming the static structure into a dynamic system that can adapt to thermal changes. This allows the shroud to flex and adjust its configuration in response to thermal expansion of the struts, maintaining stiffness balance while accommodating thermal growth.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the inner shroud is segmented into arcuate panels to accommodate thermal expansion, then thermal growth accommodation is improved, but structural complexity increases

Engineering Contradiction:

Improvethermal expansion accommodationVSAvoidshroud construction

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The arcuate panels serve multiple functions: they form the inner shroud structure, provide acoustic attenuation, and enable thermal expansion accommodation. By making the panels multi-functional, the design reduces the need for separate components and justifies the added complexity through functional integration.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The segmented panel structure allows the inner shroud to self-adjust and self-accommodate thermal expansion without requiring external mechanisms or complex control systems. The panels move relative to each other in response to thermal growth, providing automatic adaptation to thermal conditions.

Inventive Principle:

Principle #25Self-service

3Object-affected harmful factors

If acoustic panels are integrated into the inner shroud to provide sound attenuation, then acoustic performance is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvesound attenuationVSAvoidpanel assembly

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The acoustic panels are merged with the inner shroud structure, combining acoustic attenuation functionality with the structural shroud. This integration eliminates the need for separate acoustic lining components and simplifies the overall assembly process while maintaining effective sound attenuation.

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

This design reduces stress levels, increases component durability, and provides effective sound attenuation by allowing the inner shroud to thermally expand and contract, while maintaining structural integrity and minimizing weight by eliminating the need for additional frame members.

Implementation Method 1

the panels being movable relative to each other to provide for thermal expansion/contraction of the radially inner annular shroud in response to thermally induced movement of the turbine exhaust struts

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

a plurality of circumferentially spaced-apart exhaust struts extending radially across the gaspath between the radially outer and the radially inner annular shrouds

Methodology Applied

Scientific EffectAcoustic absorption: Acoustic Absorption

Data Source

PatentUS8826669B2Gas turbine exhaust case

Publication Date: 2014.09.09 PRATT & WHITNEY CANADA CORP

AI summary

A turbine exhaust case for a turbofan engine comprises a plurality of arcuate acoustic panels assembled into a circumferentially extending inner shroud with circumferential gaps between adjacent acoustic panels. An outer shroud extends circumferentially about the inner shroud. The inner shroud and the outer shroud define an annular gaspath therebetween. A plurality of circumferentially spaced-apart exhaust struts extends radially across the annular gaspath and structurally connects the individual acoustic panels forming the inner shroud to the outer shroud.