Turbofan Fan Case Rub Elements for Blade Containment
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Solution Overview
Problem
Existing turbofan fan case designs face challenges in efficiently containing blade fragments while maintaining optimal tip clearance, which affects fan performance and requires careful selection of tip clearance to prevent blade penetration through the containment fabric.
Innovation Solution
A fan case with an annular softwall sandwiched structure featuring an isogrid outer support structure, abradable tip clearance control layer, and a containment fabric layer, along with rub elements made of harder materials to direct and retain blade fragments, minimizing the outside diameter and weight while ensuring containment capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the tip clearance between fan blades and case is increased to allow for blade deformation during containment, then blade containment capability is improved, but fan performance deteriorates due to larger clearance gaps
Solution Approach 1:
The fan case is segmented into multiple functional layers: an outer case structure, an abradable tip clearance control layer, and a containment fabric layer. This segmentation allows each layer to perform its specific function - the outer case provides structural support with minimal clearance, the abradable layer controls tip clearance and absorbs blade energy, and the fabric layer contains blade fragments - thereby resolving the contradiction between containment capability and fan performance.
Solution Approach 2:
The abradable tip clearance control layer acts as an intermediary between the outer case and the containment fabric. It provides a controlled interface that allows blade tips to rub against it during containment events, absorbing energy and reducing the force transmitted to the containment fabric, thus enabling effective containment with minimal clearance and maintaining fan performance.
2Reliability
If the containment fabric layer is made thicker to improve blade containment effectiveness, then containment capability is improved, but the outer diameter and weight of the fan case increase
Solution Approach 1:
The abradable tip clearance control layer provides beforehand cushioning by absorbing blade kinetic energy through controlled rubbing before the blade reaches the containment fabric. This pre-absorption of energy reduces the force impact on the fabric, allowing it to be thinner while still maintaining effective containment capability, thus reducing fan case weight.
Solution Approach 2:
The fan case employs composite materials including the containment fabric (such as Kevlar®) combined with the abradable tip clearance control layer and the outer case structure. This composite structure achieves high containment effectiveness with reduced material usage and weight compared to a single thick fabric layer.
3Weight of stationary object
If the containment fabric layer is made thinner to reduce weight and diameter, then fan case weight is reduced, but the risk of blade penetration increases
Solution Approach 1:
The abradable tip clearance control layer provides beforehand cushioning that absorbs blade kinetic energy through controlled rubbing before the blade reaches the thinner containment fabric. This pre-absorption mechanism protects the thinner fabric from penetration while maintaining weight reduction benefits.
Solution Approach 2:
The abradable layer serves as an intermediary protective barrier between the blade and the thin containment fabric. It transfers and dissipates blade energy through controlled material removal, preventing direct impact on the fabric and enabling the use of thinner, lighter fabric while maintaining penetration resistance.
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 design reduces the outer diameter and weight of the fan case while maintaining effective blade containment, allowing for closer tolerances and reduced risk of blade penetration, thereby enhancing fan performance and reducing material usage.
Implementation Method 1
abradable tip clearance control layer
Implementation Method 2
rub elements made of harder materials to direct and retain blade fragments
Data Source
Figure 1
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AI summary
A turbofan engine (10) comprises an annular inner wall (28) surrounding tips of the fan blades (22), a layer of insulating material (30) surrounding the inner wall (28), and an outer casing (21) including an annular outer wall (32) surrounding the insulating material (30) and concentric to the inner wall (28). At least two annular rub elements (50, 150) extend radially inwardly from the outer wall (32) through only part of a radial thickness of the layer of insulating material (30). At least two of the rub elements (50, 150) are in axial alignment with the blade tips at every point around a circumference of the fan. Each rub element (50, 150) has a radially inner end (52) spaced apart from the inner wall (28) and made of a material harder than that of the blades (22). A containment fabric layer (34) is wrapped around a support structure (33) of the outer wall (32).