Counter-rotating Low Pressure Turbine Architecture for Gas Engine Length Reduction

Solution Overview

Problem

There is a conflict between achieving a high pressure core ratio and shortening the overall length of a gas turbine engine, as a long low shaft is required for desirable pressure ratios but counteracts the goal of increasing power density by lengthening the engine.

Innovation Solution

The implementation of a counter-rotating low pressure compressor and turbine architecture, with bearings positioned strategically to support the outer rotor and shaft, allowing for a reduction in engine length while maintaining high pressure core ratios through the use of roller and ball bearings and an air seal at the interface between the mid-turbine frame and outer rotor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stress or pressure

If a long low shaft is used to achieve high pressure core ratio, then the pressure ratio is improved, but the engine length increases and power density decreases

Engineering Contradiction:

Improvepressure core ratioVSAvoidengine length

Core Design Contradiction:

Stress or pressureVSLength of moving object

Solution Approach 1:

The low pressure turbine is divided into two counter-rotating sections: an inner rotor with first blade rows connected to the low shaft, and an outer rotor with second blade rows rotating in the opposite direction. This segmentation allows the shaft to be shorter while maintaining the required pressure ratio through the combined effect of both turbine sections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The outer rotor is designed to rotate in the opposite direction to the inner rotor and low shaft. This counter-rotation allows both turbine sections to extract energy from the gas flow in opposite rotational directions, effectively doubling the torque extraction capability within a compact axial length, thus achieving high pressure ratio without a long shaft.

Inventive Principle:

Principle #13The other way round (Inversion)

2Stress or pressure

If a long low shaft is used to achieve high pressure core ratio, then the pressure ratio is improved, but the power density decreases due to increased engine length

Engineering Contradiction:

Improvepressure core ratioVSAvoidpower density

Core Design Contradiction:

Stress or pressureVSPower

Solution Approach 1:

The low pressure turbine is divided into two counter-rotating sections: an inner rotor with first blade rows connected to the low shaft, and an outer rotor with second blade rows rotating in the opposite direction. This segmentation allows the shaft to be shorter while maintaining the required pressure ratio through the combined effect of both turbine sections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The outer rotor is designed to rotate in the opposite direction to the inner rotor and low shaft. This counter-rotation allows both turbine sections to extract energy from the gas flow in opposite rotational directions, effectively doubling the torque extraction capability within a compact axial length, thus achieving high pressure ratio without a long shaft.

Inventive Principle:

Principle #13The other way round (Inversion)

3Length of moving object

If counter-rotating components are used to reduce engine length, then the engine length is reduced, but the device complexity increases

Engineering Contradiction:

Improveengine lengthVSAvoidturbine architecture complexity

Core Design Contradiction:

Length of moving objectVSDevice complexity

Solution Approach 1:

The bearing system is integrated into the mid-turbine frame structure, with bearings positioned upstream of the blade rows to support both the inner and outer rotors. This merging of support functions into a single structural element reduces overall complexity compared to having separate support systems for each rotor.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The mid-turbine frame structure serves multiple functions: it provides structural support, houses the bearing system for both rotors, and positions the seals. This multi-functionality reduces the number of separate components needed, offsetting the complexity introduced by the counter-rotating architecture.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentEP2820281B1Counter-rotating low pressure turbine without turbine exhaust case

Publication Date: 2019.11.13 UNITED TECH CORP

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AI summary

A gas turbine engine includes a shaft defining an axis of rotation. An inner rotor directly drives the shaft and includes an inner set of blades. An outer rotor has an outer set of blades interspersed with the inner set of blades. The outer rotor is configured to rotate in an opposite direction about the axis of rotation from the inner rotor. A gear system is engaged to the outer rotor and is positioned upstream of the inner set of blades.