CFD Modeling of Abdominal Aortic Aneurysms

100 Pages·2015·22.02 MB·English

CFD Modeling
of Abdominal
Aortic Aneurysms
Tim van Kruchten
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CFD M
ODELING
A
OF BDOMINAL
A A
ORTIC NEURYSMS
by
TimvanKruchten
inpartialfulfillmentoftherequirementsforthedegreeof
MasterofScience
inAppliedPhysics
attheDelftUniversityofTechnology,
tobedefendedpubliclyonFridayJuly24,2015at14:00PM.
Supervisor: Dr.ir.C.Poelma, TUDelft
Thesiscommittee: Prof.dr.ir.J.Westerweel, TUDelft
Dr.ir.M.J.B.M.Pourquie, TUDelft
Dr.J.Kalkman, TUDelft
Anelectronicversionofthisthesisisavailableathttp://repository.tudelft.nl/.

A
BSTRACT
Anabdominalaorticaneurysm(AAA)isanexcessivelocalizedswellingoftheabdominalaorticwall. AAAs
areoftenlethalwhentheyruptureandconstituteasignificanthealthriskinthedevelopedcountries. CFD
simulationscanhelppredictformation,progression,andruptureofAAAsbytheuseofhemodynamicpa-
rameterssuchastheOscillatoryShearIndex(OSI)thatindicatestheoscillatorybehaviorofthewallshear
stressvectorattheaneurysmwall. Ideally,itisenvisionedthattheriskofruptureofaparticularaneurysm
canbeestimatedbypatient-specificparametersthatarecollectedfromapatientwithminimaleffortandto
classifytheaneurysmintodifferentcategoriesthatdoordonotposeaconsiderableriskofrupture.
Themainobjectiveofthisthesisthenaimstofocusontheunderlyingflowmechanismsinaneurysmflow
andtriestotakethefirststepstowardsanabstractaneurysmmodelbymeansofaproofofprincipleregard-
ing the prediction of formation, progression, and rupture locations within an aneurysm, based on simple
patient-specificinputparameters.
Tothisend,CFDsimulationsofpulsatilebloodflowinanabstractabdominalaorticaneurysm(4A)model
areperformedfortheindependentrangesofmeanReynoldsnumber300≥Re ≥1200,Womersleynumber
m
15.1≥α≥27.7,aneurysmlengthratio2.6≥Le≥5.3,andaneurysmdiameterratio1.81≥Di≥2.55. Theef-
fectofthevariationoftheinputparametersontheoscillatoryshearindex(OSI)isregardedandquantifiedby
the4Asurface-averagedOSI.GeneraltrendsshowthattheaverageOSIdecreases15percentoverthemean
Reynoldsnumberrangeof300≤Re≤1200,increases16percentovertheWomersleynumberrangeof15.1
≤Wo,α≤27.7,increases11percentovertheaneurysmlengthratiorangeof2.6≤Le≤5.3,anddecreases
5 percent over the aneurysm diameter ratio range of 1.81 ≤ Di ≤ 2.55, indicating that the mean Reynolds
numberandtheWomersleynumberhavethelargestinfluenceontheaverageOSIforthe4A.Thefluctuating
wallshearstressvectoratthestagnationpointsofthevorticespresentintheaneurysmispointedoutasthe
originofthehighOSIvaluedaxisymmetricringsfoundonthesurfaceofthe4A.Additionally,thereexistsan
inverserelationbetweenthesurface-averagedOSIandtheturbulenttoperiodickineticenergyratio,demon-
stratingtheimportanceoftheperiodiccomponents. Pulsatilebloodflowsimulationisalsoperformedona
patient-specificaneurysmgeometryandcomparedwiththe4AcasewithLe=4.6. Thedissimilarflowand
OSIresultsimplythattheinputparametersalonedonotpermittomakestatementsabouttheOSIvaluesin
thepatient-specificaneurysmbasedonthe4A.
iii

A
CKNOWLEDGEMENTS
Firstandforemost,IwouldliketothankthethesiscommitteeandespeciallymysupervisorDr. ir. Christian
Poelmaforintroducingmetotheworldofbiofluidmechanicsandthemultitudeofrelevantandlessrelevant
hemodynamicparametersthatcomewithit,aswellasforthedailyguidancethroughouttheproject. Aspe-
cialthanksgoesouttoDr.ir.MathieuPourquieforhisinexhaustibleknowledgeaboutCFD,meshgeneration,
andterminals. ThankstoProf. dr. ir. JerryWesterweelandDr. JeroenKalkmanfortakingplaceinthethesis
committeeandtakingthetimetoreadthroughthethesis.
ThetimespentintheMScstudentsroomattheLaboratoryforAero&Hydrodynamicswouldhavenotbeen
thesamewithoutthecompanyoftheotherMScstudents.SpecialthankstoAvinash,Lyckle,andYvesforthe
discussionsontheperilsofwritingaMScthesisandlifeaftergraduating.
A small, but necessary thanks is in order for my roommates at Noordeinde 11, to put graduating in per-
spectivewithother,andmostlikelymoreimportantthingsinlife.AlsothankstoMaxRadermacher,without
whoseadvicedefinitelysomeinterestingflowdetailswouldbeoverlooked.
Without Huub, Yvonne, Dyonne, Rick, and Suzanne, graduating would have surely never been an option
andIhopethatsomedayIcanreturnallthesupportreceivedduringmyyearsofstudyinginDelft.
TimvanKruchten
Delft,July10,2015
v

C
ONTENTS
1 Introduction 1
1.1 Cardiovascularsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 AbdominalAorticAneurysm(AAA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Hemodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 CFDasaclinicaltool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Projectoverview 7
2.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Theoreticalbackground 13
3.1 Pulsatileflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.1 Transitionalflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Dimensionalanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 Inputparametersandtheirranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.1 MeanReynoldsnumber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3.2 Womersley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.3 Lengthanddiameterratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.4 Outputparameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4.1 Wallshearstress(WSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4.2 OscillatoryShearIndex(OSI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4.3 Vorticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4.4 Turbulencekineticenergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.5 Viscouspropertiesofblood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4 Numericalsetup 29
4.1 Geometries/Flowdomain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.1 4A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1.2 Patient-specific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2.1 4Amesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.2.2 Patient-specificmesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3 Boundaryconditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.3.1 Inletprofile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.3.2 Pressureoutlet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4 Solversettings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.5 Simulationdetails. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.6 Post-processingwithMATLAB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5 Validation 45
5.1 Developmentofinletprofile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 OSIvaluesinstraightcylindricalpipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3 ConvergenceofOSI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
6 Results&discussion 51
6.1 Generalflowdescriptionstandardcase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
6.2 OSIdependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.2.1 Reynoldsnumberrange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.2.2 Womersleyrange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.2.3 Lengthratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
vii
viii CONTENTS
6.2.4 Diameterratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.2.5 OverallOSIdependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.3 Patient-specificaneurysm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.4 Comparisonofpatient-specificaneurysmand4A. . . . . . . . . . . . . . . . . . . . . . . . . 73
7 Conclusions&recommendations 77
7.1 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
A Appendix 81
A.1 InletprofileUDFforstandardcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
A.2 Inletprofiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
A.3 OSIandstreamlinesoverlayformeanReynoldsnumbers. . . . . . . . . . . . . . . . . . . . . 84
A.4 OSIandstreamlinesoverlayforWomersleynumbers. . . . . . . . . . . . . . . . . . . . . . . 85
A.5 OSIandstreamlinesoverlayforlengthratios . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
A.6 OSIandstreamlinesoverlayfordiameterratios. . . . . . . . . . . . . . . . . . . . . . . . . . 87
Bibliography 89