Gas Turbine Shaft Break Mitigation via Nozzle Area Reduction

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Solution Overview

Problem

In gas turbine engines, shaft breakages can lead to rapid turbine acceleration, posing a risk of turbine disintegration and damage due to over-speed events, necessitating rapid mitigation strategies to prevent disc burst and further damage.

Innovation Solution

A method and system that detect a shaft break event and activate a fluid introduction into the gas flow downstream of the turbine to reduce the nozzle's effective area, thereby decreasing the mass flow rate and terminal speed of the turbine, using a shaft break mitigation system controlled by an electronic engine controller, which can modify fuel schedules or increase reheat fuel supply to flood nozzles and adjust nozzle geometry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the turbine is allowed to accelerate freely after shaft break, then the turbine can maintain high power output, but the turbine disc may burst due to over-speed events

Engineering Contradiction:

Improveturbine power outputVSAvoidturbine disc integrity

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The system detects shaft break conditions and immediately activates mitigation measures by introducing fluid into the gas flow downstream of the turbine. This preliminary anti-action counteracts the harmful acceleration effect before the turbine disc can reach critical speeds, preventing disc burst while maintaining operational safety.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

A fluid (such as water or another liquid/gas) is introduced as an intermediary substance into the exhaust gas flow downstream of the turbine. This intermediary fluid absorbs kinetic energy and reduces the effective area of the nozzle, thereby limiting the turbine's acceleration potential without directly contacting or mechanically stopping the turbine itself.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If fluid is introduced into the gas flow downstream of the turbine to reduce terminal speed, then the risk of disc burst is reduced, but the mass flow rate through the turbine decreases

Engineering Contradiction:

Improveturbine disc safetyVSAvoidmass flow rate through turbine

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The fluid introduction is applied locally at a specific location downstream of the turbine where it can most effectively reduce nozzle area and terminal speed. The mitigation system targets the exhaust flow region rather than interfering with the entire gas path, thereby minimizing impact on overall mass flow rate while maximizing safety benefit.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system changes physical parameters of the exhaust flow by introducing fluid that alters density, viscosity, and flow area characteristics. These parameter changes reduce the effective nozzle area and terminal speed of the turbine without requiring a complete shutdown or significant reduction in overall engine mass flow rate.

Inventive Principle:

Principle #35Parameter changes

3Speed

If the nozzle effective area is reduced to limit terminal speed, then the turbine acceleration is controlled, but the energy transfer to the turbine is reduced

Engineering Contradiction:

Improveturbine terminal speedVSAvoidenergy transfer to turbine

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The fluid introduction is activated in response to detected shaft break conditions, performing preliminary action to prevent excessive acceleration. By introducing the fluid at the appropriate moment and location, the system prepares the exhaust flow to limit terminal speed while minimizing disruption to normal energy transfer operations.

Inventive Principle:

Principle #10Preliminary action

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 solution effectively reduces the risk of turbine disc burst by decreasing the terminal speed and energy transfer to the turbine post-shaft break, either by reducing gas flow energy or adjusting turbine weight, thereby maintaining safe operational speeds.

Implementation Method 1

introduces a fluid into a gas flow of the gas turbine engine downstream of the turbine... whereby the fluid reduces an effective area of a nozzle for the gas flow so as to reduce the mass flow rate of the gas flow through the turbine

Methodology Applied

Scientific EffectFluid mixing:

Implementation Method 2

The terminal speed of the turbine can therefore be reduced, as there is less energy in the gas flow to drive the (now decoupled) turbine

Methodology Applied

Scientific EffectEnergy transfer:

Data Source

PatentUS11629613B2Gas turbine engine shaft break mitigation

Publication Date: 2023.04.18 ROLLS ROYCE PLC

AI summary

A method of controlling a gas turbine engine includes the steps of: detecting a shaft break event in a shaft connecting a compressor of the gas turbine engine to a turbine of the gas turbine engine; and in response to this detection, activating a shaft break mitigation system which introduces a fluid into a gas flow of the gas turbine engine downstream of the turbine, or increases an amount of a fluid being provided into the gas flow of the gas turbine engine downstream of the turbine, whereby the fluid reduces an effective area of a nozzle for the gas flow so as to reduce the mass flow rate of the gas flow through the turbine.