Turbine Overspeed Limiting Device with Fixed Shearing Means

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Solution Overview

Problem

Existing solutions for limiting turbine overspeed in turbomachines after a turbine shaft fracture are inefficient, complex, and increase the overall mass and modify the aerodynamic profile of the turbine, while being slow to react.

Innovation Solution

A device with fixed shearing means carried by the stage of fixed blades between the upstream and downstream disks of the rotor, which shears the moving blades at the start of downstream displacement, preventing overspeed by destroying them and projecting them onto other blades, thus stopping mechanical energy transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mechanical braking means are used to brake the turbine rotor after shaft fracture, then the rotor speed is limited, but the response time is slow reducing efficiency

Engineering Contradiction:

Improveoverspeed limitationVSAvoidresponse time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The fixed shearing means are pre-positioned on the stator such that when the rotor displaces downstream after shaft fracture, the moving blades immediately contact and are sheared by these pre-positioned means. This eliminates the delay associated with activating mechanical brakes, as the destructive action begins instantly upon rotor displacement, rapidly limiting overspeed

Inventive Principle:

Principle #10Preliminary action

2Reliability

If guide blades are made detachable or pivoting to destroy moving blades during rotor displacement, then overspeed is limited, but the device complexity and cost increase

Engineering Contradiction:

Improveoverspeed limitationVSAvoidblade mechanism complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of making the guide blades detachable or pivoting as in conventional solutions, the invention fixes the shearing means firmly on the stator. The moving blades are designed with fragile struts that are intended to be sheared. This inversion simplifies the device by eliminating complex mounting mechanisms while achieving the same protective function through the fragility of the moving blade struts

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If protective means are added to prevent turbine overspeed, then safety is improved, but the overall mass of the turbine increases

Engineering Contradiction:

Improvesafety against overspeedVSAvoidturbine mass

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The moving blades incorporate fragile struts that are inherently designed to break under overspeed conditions. When the rotor displaces downstream after shaft fracture, these self-contained fragile elements automatically shears against the fixed shearing means, eliminating the need for additional heavy protective components. The blades themselves provide the protective function through their deliberate fragility

Inventive Principle:

Principle #25Self-service

4Reliability

If additional protective components are installed to limit overspeed, then reliability is improved, but the aerodynamic profile of turbine components is modified

Engineering Contradiction:

Improveoverspeed protectionVSAvoidaerodynamic profile

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The shearing means are merged with the existing stator structure, utilizing the fixed blades that are already part of the turbine's aerodynamic path. This integration ensures that the protective function is achieved without adding separate components that would disrupt gas flow or modify the aerodynamic profile of the turbine

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

The solution quickly and effectively prevents turbine overspeed, eliminating the risk of explosion and perforation, without modifying the gas flow or reducing performance, and is simpler and less costly to produce than existing methods.

Implementation Method 1

these means of destruction are fixed and carried by a stage of fixed blades situated between the upstream disk of the rotor and the following disk of that rotor and are intended to shear the blades of the upstream disk of the rotor

Methodology Applied

Scientific EffectShear stress: Shear Stress

Data Source

PatentUS7484924B2Device for limiting turbine overspeed in a turbomachine

Publication Date: 2009.02.03 SAFRAN AIRCRAFT ENGINES SAS

AI summary

Device for limiting turbine overspeed in a turbomachine, the turbine comprising a rotor formed of disks mounted on a turbine shaft and carrying moving blades, stages of fixed blades disposed between the disks of the rotor, and means for shearing the moving blades of the upstream disk of the rotor, these means being carried by a circumferential rim of a stage of fixed blades of the turbine.