Turbomachine Fan Hub Design for Mass Reduction

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Solution Overview

Problem

Current turbomachines with small inlet diameters face challenges in reducing the external diameter of the fan hub due to mechanical strength, torsional resistance, and manufacturing constraints, limiting performance and mass reduction.

Innovation Solution

A compact fan design with an annular cowl and upstream flange arrangement, featuring a scalloped radial edge for axial retention and a ring with radial projections for rotational immobilization, allows for a smaller mass and more flexible design, eliminating downstream axial retention hooks and using thinner shims and a titanium alloy for the fan disc.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If the hub ratio of the turbomachinery fan is reduced to decrease mass and improve performance, then the external diameter of the hub can be reduced, but current manufacturing and mechanical constraints prevent the hub diameter from being reduced below 570-585 mm

Engineering Contradiction:

Improvemass of turbomachineVSAvoidradial mechanical strength of blades

Core Design Contradiction:

Weight of moving objectVSStrength

Solution Approach 1:

The retaining means is segmented into multiple functional elements: an annular flange with scalloped section for axial retention, a ring with radial projections for rotational immobilization, and integration with the low-pressure compressor structure. This segmentation allows each element to perform its specific function efficiently, enabling the overall hub diameter to be reduced while maintaining blade retention strength.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The retaining means is merged with the low-pressure compressor structure by engaging the scalloped section of the flange with the scalloped section of the compressor. This merging eliminates the need for separate downstream retaining hooks and integrates multiple functions into a unified structure, reducing the required hub diameter while maintaining blade retention capability.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If downstream axial retention hooks are used to prevent blade movement, then blade retention is achieved, but the mechanical components require larger radial dimensions that increase hub size and mass

Engineering Contradiction:

Improveblade retentionVSAvoidradial dimension of mechanical components

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The downstream axial retention hooks are extracted from the design entirely. Instead, axial retention is achieved through the upstream annular flange with scalloped section that engages with the low-pressure compressor. This extraction eliminates the radial space requirements for downstream hooks while maintaining reliable blade retention through the upstream retaining mechanism.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The low-pressure compressor structure serves multiple functions: it acts as both the downstream compressor component and the downstream retaining structure through its scalloped section engagement with the flange. This multi-functionality eliminates the need for separate downstream retention hooks, reducing radial dimensions while maintaining blade retention reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If thicker shims are used to engage blade root hooks and hold blades in raised position, then blade retention is secured, but the radial space required increases the hub diameter

Engineering Contradiction:

Improveblade retention positionVSAvoidradial space for shims

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The thick shims required for downstream blade retention are extracted from the design by eliminating the downstream hook mechanism. Instead, blade position control is achieved through the upstream flange and ring structure, which provides axial and rotational retention without requiring radial space for thick shims.

Inventive Principle:

Principle #2Taking out (Extraction)

4Weight of moving object

If the hub diameter is reduced below current standards, then mass and performance are improved, but manufacturing methods and tooling accessibility become problematic

Engineering Contradiction:

Improvemass of turbomachineVSAvoidmanufacturing and tooling accessibility

Core Design Contradiction:

Weight of moving objectVSEase of manufacture

Solution Approach 1:

Instead of reducing the overall hub diameter and accepting manufacturing challenges, the invention inverts the approach by maintaining adequate manufacturing access through the upstream flange structure while achieving the functional equivalent of a reduced hub through the integrated retaining means. The scalloped flange and ring structure provides manufacturing accessibility while achieving the mass reduction goals.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentEP3074639B1Fan, in particular for a turbo engine, and flange for said fan

Publication Date: 2020.02.05 SAFRAN AIRCRAFT ENGINES SAS

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AI summary

The invention relates to a fan, in particular for a small turbine engine such as a jet engine, having a hub ratio corresponding to the ratio of the diameter of the inner limit of the air intake section (26) at the radially internal ends of the leading edges of the fan blades (10), divided by the diameter of the circle through which the outer ends of the fan blades pass, which has a value of 0.25 to 0.27.