Combustor Liner Fastener Segmentation for Thermal Deflection

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Solution Overview

Problem

In gas turbine engine combustors, the large clearance holes used to accommodate thermal deflections in heat shields result in inaccuracies in the location of critical features like fuel injectors, which is problematic in smaller engines due to reduced space and manufacturing tolerances, and increased thermal deflections.

Innovation Solution

A combustor liner design with specific fastener configurations, including positioning holes, circumferential slots, and clearance holes, that allow controlled radial and circumferential motion to accommodate thermal deflections while maintaining accurate positioning of heat shields and fuel nozzles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If large clearance holes are used to accommodate thermal deflections, then the heat shield can move freely with thermal expansion, but the location accuracy of critical features such as fuel injector deteriorates

Engineering Contradiction:

Improvethermal deflection accommodationVSAvoidlocation accuracy of fuel injector

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The fastening system is segmented into three distinct types of openings: positioning holes for precise radial and circumferential location, circumferential slots for controlled circumferential motion only, and clearance holes for radial motion accommodation. This segmentation allows each opening type to serve a specific function in managing thermal deflections while maintaining overall positioning accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the heat shield fastening system are assigned different degrees of freedom based on local requirements. The positioning hole provides fixed positioning where precision is critical, the circumferential slot allows motion in one direction only where thermal expansion occurs primarily circumferentially, and the clearance hole allows full motion where maximum thermal deflection accommodation is needed.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If clearance holes are used to retain heat shield fasteners, then thermal deflections are accommodated, but the location inaccuracy becomes problematic in smaller engines with reduced space and tighter tolerances

Engineering Contradiction:

Improvethermal deflection accommodationVSAvoidlocation accuracy in small engines

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The fastening system transitions from a static fixed-hole approach to a dynamic multi-mode system where different openings provide different levels of motion freedom. The positioning holes provide static precision, while the circumferential slots and clearance holes provide dynamic adaptation to thermal changes, allowing the system to maintain reliability across varying thermal conditions and engine sizes.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The circumferential slot acts as an intermediary between the fully constrained positioning hole and the fully free clearance hole. It provides a intermediate level of constraint that allows controlled circumferential motion while maintaining radial positioning, serving as a mediator that balances the need for precision with the need for thermal accommodation in space-constrained small engine applications.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If internal fuel manifold is included in smaller engines, then fuel distribution is improved, but relative thermal deflections increase requiring larger clearance holes which worsens location inaccuracy

Engineering Contradiction:

Improvefuel distribution capabilityVSAvoidheat shield location accuracy

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The fastening system is segmented into different constraint levels to handle the increased thermal deflections caused by the fuel manifold. The positioning holes maintain precise radial and circumferential location, the circumferential slots accommodate circumferential expansion from the manifold, and the clearance holes allow additional radial motion, collectively managing the thermal effects of the fuel manifold without compromising overall positioning accuracy.

Inventive Principle:

Principle #1Segmentation

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

The design effectively accommodates thermal deflections, ensuring accurate positioning of heat shields and fuel nozzles, reducing inaccuracies and improving the reliability of smaller gas turbine engines.

Implementation Method 1

The limited circumferential motion of the second fastener within the slot and the limited radial and circumferential motion of the third fastener within the clearance hole accommodating a difference in thermal expansion between the dome section and each of the heat shield portions

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS7845174B2Combustor liner with improved heat shield retention

Publication Date: 2010.12.07 PRATT & WHITNEY CANADA CORP

AI summary

A combustor liner including a dome section having a positioning hole defined at a first radial distance and sized to receive a first heat shield fastener to at least substantially prevent radial and circumferential motion of the first fastener, a circumferential slot sized to receive a second heat shield fastener to at least substantially prevent radial motion of the second fastener while allowing limited circumferential motion of the second fastener, and a clearance hole defined at a second radial distance and sized to receive a third heat shield fastener to allow limited radial and circumferential motion of the third fastener.