Turbomachine Rotor Bulb Retaining Part Design

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Solution Overview

Problem

Turbomachine blades made of Ceramic Matrix Composite (CMC) experience stresses due to differing expansion coefficients with metal rotor disks, leading to additional stresses and reduced mechanical strength, particularly at the bulb-root connection, which limits the material available for disk teeth strength.

Innovation Solution

A turbomachine rotor design featuring a bulb with a radially inward-opening slot and a retaining part that projects outwards from the groove, allowing increased bearing area without enlarging the bulb dimensions, and a disk with a radially outward slot to accommodate the retaining part, thereby reducing bulb size and mass while maintaining strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the lateral dimensions of the bulb are increased to resist stresses from CMC blades, then the blade can resist thermal expansion stresses, but the lateral dimensions of the groove must also increase, which limits the quantity of material available for mechanical strength of the disk teeth

Engineering Contradiction:

Improveblade stress resistanceVSAvoiddisk tooth material area

Core Design Contradiction:

StrengthVSArea of stationary object

Solution Approach 1:

The patent introduces a retaining part that extends into the groove from the disk, creating an additional bearing dimension. The retaining part has a bearing surface that contacts the bulb, effectively adding a new dimension to the bearing area without increasing the lateral dimensions of the groove or bulb. This allows the bulb to resist thermal expansion stresses while maintaining sufficient disk tooth material area.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The bearing function is segmented between two distinct components: the groove in the disk and the retaining part extending from the disk. The retaining part is separated from the main disk body but works together with it to provide the necessary bearing support. This segmentation allows the bearing area to be increased without proportionally increasing the groove dimensions.

Inventive Principle:

Principle #1Segmentation

2Stress or pressure

If the bulb bearing area is increased to reduce stresses, then the bulb can better resist compression and shear stresses, but the bulb dimensions would need to increase, increasing the rotor mass

Engineering Contradiction:

Improvebulb bearing stressVSAvoidrotor mass

Core Design Contradiction:

Stress or pressureVSWeight of moving object

Solution Approach 1:

The retaining part acts as an intermediary element between the disk and the bulb. It provides additional bearing support to the bulb without requiring the bulb itself to be larger. The retaining part transfers loads from the bulb to the disk, effectively increasing the bearing area while keeping the bulb dimensions and thus the rotor mass unchanged.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If CMC blades are used to reduce mass and improve heat resistance, then the blade mass is lower and combustion gas resistance is better, but the different expansion coefficients generate additional stresses on the blade and internal clearances

Engineering Contradiction:

Improvecombustion gas resistanceVSAvoidthermal expansion stress

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The patent modifies the bearing geometry parameters by introducing the retaining part with specific bearing surfaces. The retaining part's bearing surface is positioned and dimensioned to provide optimal support against thermal expansion stresses. This parameter change allows the system to accommodate the different expansion coefficients of CMC blades and metal disk while reducing the generated stresses.

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

This design effectively distributes stresses across the bulb and disk, enhancing the bulb's bearing capacity and maintaining disk tooth strength, even with CMC blades, by increasing the bulb's bearing area without increasing its size, thus addressing the stress issues and material limitations.

Implementation Method 1

a radially outer end of the retaining part fits into the slot of the bulb and bears radially inwards on the inner wall of the slot in the bulb

Methodology Applied

Scientific EffectMechanical bearing contact: Friction

Implementation Method 2

Cooperation between the bulb and the groove holds the blade connected to the disk, despite forces generated by centrifugal action when the rotor rotation speed is high

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Implementation Method 3

These two materials have different expansion coefficients, which can consequently generate additional stresses on the blade, or internal clearances due to the different expansions of the components as the temperature varies in the turbomachine

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10072508B2Turbomachine rotor with optimised bearing surfaces

Publication Date: 2018.09.11 SAFRAN AIRCRAFT ENGINES SAS

AI summary

The invention relates to a turbomachine rotor including a disk and at least one blade wherein the root comprises a bulb accommodated into a groove associated with the disk, wherein the bulb includes a slot that opens up radially inwards at its lower face, and in that the rotor includes a retaining part extending partly into the groove projecting radially outwards from the bottom face of the groove, of which a radially outer end of the retaining part fits into the slot of the bulb and bears radially inwards on the inner wall of the slot of the bulb.