Cambered Fan Blade Root Sections for 1F Mode Frequency

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Reducing the first bending mode of fan blades in small-diameter airplane turbojets to prevent unstable vibratory behavior and cracking, while avoiding weight and performance penalties.

Innovation Solution

Introducing a fan blade design with a cambered profile featuring a point of inflection in the skeleton curve for airfoil sections between the root and 30% radial height, which increases the 1F mode frequency without increasing the blade's chord or root section thickness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the hub ratio of the fan is reduced to increase specific flow rate and thrust, then the engine performance is improved, but the first resonant mode frequency of the blades decreases leading to unstable vibratory behavior

Engineering Contradiction:

Improvespecific flow rateVSAvoidblade stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies local quality by introducing a cambered profile specifically in the root sections (0-30% radial height) of the fan blades, while the rest of the blade maintains its original profile. This localized modification increases the 1F mode frequency and stabilizes the blade without affecting the overall blade design or requiring changes to the fan hub ratio, thus resolving the contradiction between improved productivity and maintained reliability.

Inventive Principle:

Principle #3Local quality

2Reliability

If the chord of the blade is increased to increase the 1F mode frequency, then the blade stability is improved, but the length and weight of the turbojet increase

Engineering Contradiction:

Improveblade stabilityVSAvoidblade length

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

Instead of increasing the chord length of the entire blade, the patent applies a cambered profile locally only to the root sections (0-30% radial height). This localized approach increases the 1F mode frequency and improves blade stability without increasing the overall blade length or the turbojet dimensions, thus resolving the contradiction between reliability and length.

Inventive Principle:

Principle #3Local quality

3Reliability

If the root section of the blade is thickened to increase the 1F mode frequency, then the blade stability is improved, but the weight of the fan and turbojet increases significantly

Engineering Contradiction:

Improveblade stabilityVSAvoidfan weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent introduces a cambered profile in the root sections (0-30% radial height) which modifies the shape rather than increasing the thickness. This local geometric modification increases the 1F mode frequency and improves blade stability without adding significant material or weight to the fan, thus resolving the contradiction between reliability and weight.

Inventive Principle:

Principle #3Local quality

4Reliability

If the root section of the blade is thickened to increase the 1F mode frequency, then the blade stability is improved, but the aerodynamic performance of the turbojet deteriorates

Engineering Contradiction:

Improveblade stabilityVSAvoidaerodynamic performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The cambered profile is applied locally to the root sections (0-30% radial height) rather than the entire blade. This localized modification minimizes the impact on the aerodynamic performance of the blade while still achieving the goal of increasing the 1F mode frequency and improving stability, thus resolving the contradiction between reliability and productivity.

Inventive Principle:

Principle #3Local quality

5Reliability

If the root section of the blade is thickened to increase the 1F mode frequency, then the blade stability is improved, but the risk of blocking at the fan root increases

Engineering Contradiction:

Improveblade stabilityVSAvoidblocking risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent modifies the shape of the root sections through a cambered profile rather than increasing the thickness. This local geometric change increases the 1F mode frequency and improves stability without increasing the radial height or chord at the root, thus avoiding the blocking risk that would result from thickening the root section.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11333164B2Airplane turbojet fan blade of cambered profile in its root sections

Publication Date: 2022.05.17 SAFRAN AIRCRAFT ENGINES SAS

AI summary

A fan blade for an airplane turbojet, the blade including an airfoil extending axially between a leading edge and a trailing edge and including a plurality of airfoil sections stacked radially between a root section and a tip section. All of the airfoil sections situated between the root section and an airfoil section situated at a radial height corresponding to 30% of a total radial height of the airfoil possess a skeleton curve having a point of inflection.