Numerical Simulation of Aircraft Ditching of a Generic Transport Aircraft Aerospace Engineering

94 Pages·2015·22.44 MB·English

by  Joel Bruno Gomes

Numerical Simulation of Aircraft Ditching of a
Generic Transport Aircraft
Implementation of an Aerodynamic Model
Joel Bruno Gomes
Thesis to obtain the Master of Science Degree in
Aerospace Engineering
Supervisors: Prof. Afzal Suleman
Dipl.-Ing. Martin Siemann
Examination Committee
Chairperson: Prof. Fernando Jos´e Parracho Lau
Supervisor: Prof. Afzal Suleman
Members of the Committee: Prof. Jo˜ao Manuel Melo de Sousa
November 2015

Acknowledgments
First and foremost, I would like to express my deepest gratitude to my supervisor Martin Siemann for
alltheknowledge, feedbackandsupportduringtheexecutionofthisthesis. Hisoverallguidanceenabled
me to complete my work with great motivation.
Besides my advisor, I would like to thank the rest of my colleagues at DLR Institute of Structures and
Design for all the assistance and intellectual support provided during this work.
My sincere thanks also goes to my supervisor at Instituto Superior T´ecnico, Prof. Afzal Suleman for
taking me as his student, for his advice and revision of this document.
A special thanks goes to all the great friends that I have met around Europe, for the support, friendship
and for sharing all the good moments that made these last five years memorable.
Additionally, I would like to thank to Qi for all the encouragement, patient and joy throughout the
years.
Finally, Iwouldliketothankmyfamily: tomysisterforsupportingmespirituallythroughouttheyears,
to my father for his example and advices, and to my mother for being the most kind and patient person
that I have ever met. Without them, all of this would not have been possible.
Lisbon, October 2015,
Joel Gomes
iii

Resumo
A certifica¸c˜ao de aeronaves requer uma an´alise de aterragem de emergˆencia em ´agua (amaragem) para
assegurar a seguran¸ca dos passageiros. De forma a apoiar o processo de design e certifica¸c˜ao, modelos
para simulac¸˜oes num´ericas de amaragem de aeronaves est˜ao a ser desenvolvidos.
NasequˆenciadotrabalhodesenvolvidonoprojetoSMAES(SMartAircraftinEmergencySituations,2011-
2014), que consistiu no refor¸co das capacidades de simula¸c˜ao para a an´alise de amaragem de aeronaves,
o DLR est´a a transferir o conhecimento adquirido para amaragem de aeronaves em escala real. Devido
`a complexidade envolvida na modela¸c˜ao em escala real, uma ferramenta de pr´e-processamento est´a at-
ualmente em desenvolvimento de forma a permitir uma gerac¸˜ao autom´atica de modelos de amaragem de
aeronaves em escala real para o c´odigo expl´ıcito Virtual Performance Solution (VPS).
O objetivo geral deste trabalho´e implementar e validar um modelo aerodinˆamico na simula¸c˜ao num´erica
deformaapermitirumamelhoriadoestadodaartedeamaragemdeaeronavesemescalareal. Omodelo
desenvolvidocalculafisicamenteascargascomequa¸c˜oesaerodinˆamicasadequadas,edestaformamelhora
fortemente a previsibilidade das cargas que ocorrem durante uma simula¸c˜ao de amaragem.
Para a implementa¸c˜ao do modelo aerodinˆamico na simulac¸˜ao num´erica, ´e proposta a cria¸c˜ao de um
novo m´odulo na ferramenta de pr´e-processamento. O c´alculo aerodinˆamico da sustenta¸c˜ao, arrasto e
momento de picada, com base na evolu¸c˜ao do ˆangulo de ataque e velocidade de voo, ´e realizado com
a implementa¸c˜ao de uma external user subroutine na simulac¸˜ao num´erica. A superioridade do modelo
aerodinˆamicodesenvolvidosobreoestadodaarte´edemonstradacombasenacompara¸c˜aodosresultados
de estudos de sensibilidade e de parˆametros.
Palavras-chave:
Amaragemdeaeronavesdeasafixa,simula¸c˜aonum´erica,modeloaerodinˆamico,
external user subroutine.
v

Abstract
Aircraftcertificationrequirestheanalysisofwateremergencylanding(ditching)withrespecttopassenger
safety. In order to support the design and certification processes, models for numerical simulation of
aircraft ditching are being developed.
Following the work developed in the SMAES project (SMart Aircraft in Emergency Situations, 2011-
2014), which consisted in the enhancing of simulation capabilities for aircraft ditching analysis, DLR is
transferringtheacquiredknowledgetofull-scaleaircraftditching. Duetothecomplexityinvolvedinfull-
scale modeling, a pre-processing tool is currently under development for an automatic model generation
of full-scale aircraft ditching models for the explicit solver Virtual Performance Solution (VPS).
The overall goal of this work is to implement and validate an aerodynamic model in the numerical
simulation to allow an improvement in the state of the art of full-scale aircraft ditching. The developed
model physically calculates the loads with proper aerodynamic equations and strongly improves the
predictability of loads occurring during a ditching simulation.
For the implementation of the aerodynamic model in the numerical simulation, the creation of a new
module in the pre-processing tool is proposed. The aerodynamic calculation of lift, drag and pitch
moment, based on the evolution of the angle of attack and flight velocity, is accomplished with the
implementation of an external user subroutine within the numerical simulation. The superiority of the
developed aerodynamic model over the state of the art is demonstrated based on comparison of results
of sensitivity and parameter studies.
Keywords:
Fixed-wing aircraft ditching, numerical simulation, aerodynamic model, external user
subroutine.
vii

Contents
Acknowledgments iii
Resumo v
Abstract vii
List of Symbols xi
List of Figures xiv
List of Tables xvi
Notation xvii
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives and structure of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Ditching of fixed-wing aircraft 5
2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Airworthiness regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Current analysis and certification procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Numerical simulation approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 Smoothed Particle Hydrodynamics (SPH) . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.2 Coupled FE-SPH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.3 State of the art of coupled FE-SPH. . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5 Pre-processing tool AC-Ditch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.6 Critical review and definition of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3 Aerodynamics 21
3.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.1 Governing equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.2 LIFTING LINE tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1.3 High-lift devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.4 Ground effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 Aerodynamics module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2.1 Integration into AC-Ditch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2.2 Aerodynamic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 External user subroutine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
ix
4 Validation 41
4.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3 Final remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5 Numerical investigations 49
5.1 Simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.2 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.2.1 Comparison of conventional lift model against aerodynamic model . . . . . . . . . 52
5.2.2 Influence of aerodynamic drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.2.3 Influence of aerodynamic pitch moment . . . . . . . . . . . . . . . . . . . . . . . . 55
5.2.4 Comparison of lift model against aerodynamic model with presence of suction . . . 57
5.3 Parametric analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.3.1 COG position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.3.2 Weight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.3.3 Impact conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6 Conclusions 69
6.1 Achievements and major findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Bibliography 71
A The Common Parametric Aircraft Configuration Schema - CPACS 75
x