Gas Turbine Rotor Motoring for Bowed Start Mitigation

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Solution Overview

Problem

Gas turbine engines face a 'bowed rotor' condition due to thermal expansion after shutdown, which makes it undesirable to restart the engine, as it can lead to high amplitude oscillations and blade tip rubbing, posing a risk of engine damage.

Innovation Solution

A bowed rotor start mitigation system that uses aircraft-derived parameters to infer engine thermal conditions, employing dry motoring with a controlled starter valve to gradually increase rotor speed, monitoring vibration levels, and adjusting the dry motoring profile to prevent high-speed resonance and reduce vibration, thereby mitigating the bowed rotor risk.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the engine is restarted after shutdown, then the engine can resume operation, but thermal expansion may cause bowed rotor condition leading to high amplitude oscillations and blade tip rubbing

Engineering Contradiction:

Improveengine operation resumptionVSAvoidengine safety

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system performs preliminary detection of thermal parameters (inferred from aircraft parameters like thrust level, flight phase, and ambient temperature) before allowing engine restart. This preliminary assessment prevents restart under bowed rotor conditions by evaluating whether the engine has cooled sufficiently after shutdown

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors aircraft parameters and uses feedback control to determine when the engine thermal state is safe for restart. The controller adjusts the restart authorization based on real-time thermal condition assessment, creating a closed-loop safety mechanism

Inventive Principle:

Principle #23Feedback

2Temperature

If thermal expansion is allowed to occur naturally after shutdown, then the engine cools down, but this extends the time before safe restart is possible

Engineering Contradiction:

Improveengine coolingVSAvoidrestart delay

Core Design Contradiction:

TemperatureVSLoss of time

Solution Approach 1:

The system replaces direct temperature sensing with an inference-based thermal model that uses readily available aircraft parameters (thrust level, flight phase, ambient temperature) to estimate engine thermal state. This substitution enables faster thermal condition assessment without requiring physical temperature sensors or extended cooling periods

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system changes the measurement parameters from direct temperature readings to inferred thermal parameters derived from aircraft operational data. This parameter transformation allows rapid thermal state evaluation and accelerates the decision-making process for safe restart timing

Inventive Principle:

Principle #35Parameter changes

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

Effectively prevents engine damage by homogenizing temperatures and reducing vibration, allowing safe engine startup without risking high amplitude oscillations or blade tip rubbing, thus ensuring reliable engine operation.

Implementation Method 1

When the gas turbine engine of an airplane has been shut off for example, after an airplane has landed at an airport, the engine is hot and due to heat rise, the upper portions of the engine will be hotter than lower portions of the engine. When this occurs thermal expansion may cause deflection of components of the engine which may result in a 'bowed rotor' condition.

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

a vibration monitor is used to set a maintenance flag based on detecting a vibration level that exceeds a maintenance action threshold while accelerating the starting spool of the gas turbine engine

Methodology Applied

Scientific EffectVibration: Vibration

Data Source

PatentUS11274604B2Bowed rotor start mitigation in a gas turbine engine using aircraft-derived parameters

Publication Date: 2022.03.15 RTX CORP

AI summary

A bowed rotor start mitigation system for a gas turbine engine of an aircraft is provided. The bowed rotor start mitigation system includes a motoring system and a controller coupled to the motoring system and an aircraft communication bus. The controller is configured to determine at least one inferred engine operating thermal parameter based on at least one aircraft-based parameter received on the aircraft communication bus, where the at least one inferred engine operating thermal parameter is based on data describing a history of the aircraft before an engine shutdown. The motoring system is controlled to drive rotation of a starting spool of the gas turbine engine below an engine idle speed based on determining that the at least one inferred engine operating thermal parameter is within a preselected range.