A Conceptual Design Methodology For Acoustic Fatigue Mitigation

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A Conceptual Design Methodology For Acoustic
Fatigue Mitigation
MSc in Integrated Aerospace Systems Design (IASD)

• Rafic.M.Ajaj
• Project Advisor Dr.Giuliano Allegri

14/10/2009
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Contents

• Objectives
• Problem Definition
• Methodology Outline
• Noise Estimation Process
• Parametric Study
• Costing Analysis
• Conclusions

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Objectives

• To establish a conceptual design methodology in a
  multi-disciplinary framework for acoustic fatigue
  mitigation in aircraft structures positioned
  close to engine efflux
• To generalize the applicability of this
  methodology to cover most aircraft morphologies
  and advanced aerospace material systems
• To illustrate, in the format of a case study
  covering three aerospace materials, the material
  system with the superior fatigue performance
• To elaborate the significance of acoustic fatigue
  problems on innovative aircraft morphologies
  powered by 2020 turbofans
• To reduce the number of design iterations during
  the conceptual design phase, and yield more
  accurate outcomes

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• Problem Definition
• The need to establish a methodology to mitigate
  acoustic fatigue is driven by the followings
• Passive airframe/engine shielding using
  innovative morphologies(BWB) leads to increase in
  localized exposure of airframe components to
  acoustic loading
• The market demand for more electric aircrafts
  urges to adopt more powerful engines thus
  increasing noise emissions
• Crack initiation and propagation due to acoustic
  fatigue have significant impacts on the
  inspection frequencies
• Development of new aerospace materials (FRP,FML)
  that have widely different dynamic
  characteristics under acoustic loadings
• High costs associated with structural failures

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• Methodology Outline
• quantifying noise emission from an ACARE 2020
  compliant turbofan engine and identify the
  skin/stringer panel subject to the highest
  acoustic loading
• 2. conducting a parametric study over
  safe-life critical skin/stringer panels designs
  with different geometries and made-up from
  different materials, and estimate their
  cumulative endurance
• estimating the costs associated with safe-life
  design of structural panels subjected to sonic
  loading
• To simplify the process, Aquila is used as a
  reference aircraft
• (i.e. a design that doesnt lead to cascade
  failure over the design life of the vehicle)

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• Noise estimation Process

• Noise mapping is performed over the lower wing
  panel of Aquila to define the critical panel
  which is subject to the highest acoustic level.

The noise level varies significantly over the
critical panel at various flight segments
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• Parametric Study
• The study consists of five major steps
• Estimate the natural frequency of the critical
  panel
• (Using Lin semi-analytical method)
• Estimate the RMS stress/strain at each flight
  segment
• (Using ESDU 73014 method)
• Obtain the endurance using safe-life design
  curves at each flight segment
• (Using S-N curves from ESDU applying a
  scatter factor)
• Estimate the total number of missions flown prior
  to cracks initiation using Miners Rule and
  present them in the form of nomographs
• Couple the nomographs with the SEER-H costing
  tool (bottom-up) for the Aquila case to show the
  impact of safe-life design on the cost of the
  panels

To generalize the applicability of such study,
the geometry of different critical skin/stringer
panels( thickness, stringer pitch) has been
varied for different materials
Al2024-T3,Glare-3,and CFEP
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Superior fatigue performance of CFEP
It points out that CFEP panels have the best
acoustic fatigue performance followed by
Glare-3,and finally Al 2024-T3 panels
To illustrate that CFEP panels have superior
fatigue performance over panels made from other
material systems, three critical skin/stringer
panels of T-tail conventional aircraft are
considered they have the same geometry but are
made from different materials
CFEP proves to be the best candidate materials
for skin/stringer panels positioned close to the
jet efflux, as it eliminates all costs associated
with heavy inspection and maintenance processes.
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• Costing Analysis for Aquilas Critical panels
• A detailed costing analysis is performed on three
  safe-life critical skin/stringer panels made-up
  from different materials for Aquila.

• CFEP panels offer significant weight saving over
  other materials (44 compared to Al 2024-T3and
  47 compared to hybrid Glare-3)

The impact of safe-life design on cost and weight
for Aquilas critical panels is as follows

• CFEP panel is the most expensive followed by
  Hybrid Glare-3 then Al 2024 T3

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Conclusions

• Innovative shielding techniques and the shift
  toward more powerful engines increase noise
  emissions and lead to the arise of acoustic
  fatigue problems
• CFEP has the superior acoustic fatigue
  performance followed by Glare-3, then Al
  2024-T3, hence its the best candidate material
  for skin/stringer panels positioned close to the
  engine efflux for most transport aircraft types
• CFEP panels offer significant weight savings over
  other materials (44 compared to Al 2024-T3and
  47 compared to hybrid Glare-3) however, they
  are much more expensive compared to other panels
• Glare offers the possibility of using hybrid
  structures which can lead to huge cost savings
  with small weight penalties.
• The Parametric study associated nomographs
  reduces the size of the design space of all
  candidate panels,which will save cost and time
  and reduce risk during the pre-design phase
• The trade-off between fatigue performance, cost,
  and weight depends mainly on the design drivers
  and applications

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Thank You For Listening
Any Question(s)?
This research will be published in The
Aeronautical Journal