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//INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–1–[1–8/8]29.3.20053:23PM Computational Fluid Dynamics Computational Fluid Dynamics: Applications in Environmental Hydraulics. Edited by P.D. Bates, S.N. Lane and R.I. Ferguson Copyright  2005 John Wiley & Sons, Ltd. ISBN: 0-470-84359-4 (HB) //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–3–[1–8/8]29.3.20053:23PM Computational Fluid Dynamics Applications in Environmental Hydraulics Editors PAULD.BATES UniversityofBristol STUARTN.LANE UniversityofDurham ROBERTI.FERGUSON UniversityofDurham //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–4–[1–8/8]29.3.20053:23PM Copyright(cid:1)2005 JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester, WestSussexPO198SQ,England Telephone (þ44)1243779777 Email(forordersandcustomerserviceenquiries):[email protected] VisitourHomePageonwww.wiley.com AllRightsReserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystemor transmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recording,scanningor otherwise,exceptunderthetermsoftheCopyright,DesignsandPatentsAct1988orunderthetermsof alicenceissuedbytheCopyrightLicensingAgencyLtd,90TottenhamCourtRoad,LondonW1T4LP, UK,withoutthepermissioninwritingofthePublisher.RequeststothePublishershouldbeaddressedto thePermissionsDepartment,JohnWiley&SonsLtd,TheAtrium,SouthernGate,Chichester,West SussexPO198SQ,England,[email protected],orfaxedto(þ44)1243770620. 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OtherWileyEditorialOffices JohnWiley&SonsInc.,111RiverStreet,Hoboken,NJ07030,USA Jossey-Bass,989MarketStreet,SanFrancisco,CA94103-1741,USA Wiley-VCHVerlagGmbH,Boschstr.12,D-69469Weinheim,Germany JohnWiley&SonsAustraliaLtd,33ParkRoad,Milton,Queensland4064,Australia JohnWiley&Sons(Asia)PteLtd,2ClementiLoop#02-01,JinXingDistripark,Singapore129809 JohnWiley&SonsCanadaLtd,22WorcesterRoad,Etobicoke,Ontario,CanadaM9W1L1 Wileyalsopublishesitsbooksinavarietyofelectronicformats.Somecontentthatappearsinprintmay notbeavailableinelectronicbooks. LibraryofCongressCataloginginPublicationData Computationalfluiddynamics:applicationsinenvironmentalhydraulics/editors, PaulD.Bates,StuartN.Lane,RobertI.Ferguson. p. cm. Includesbibliographicalreferencesandindex. ISBN-13978-0-470-84359-8(HB) ISBN-100-470-84359-4(HB) 1. Environmentalhydraulics—Mathematicalmodels. 2. Fluiddynamics—Mathematical models. I. Bates,PaulD. II. Lane,StuartN. III. Ferguson,RobertI. TC163.5.C662005 6270.042—dc22 2004028499 BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN-13978-0-470-84359-8(HB) ISBN-100-470-84359-4(HB) Typesetin10/12ptTimesbyIntegraSoftwareServicesPvt.Ltd,Pondicherry,India PrintedandboundinGreatBritainbyAntonyRoweLtd,Chippenham,Wiltshire Thisbookisprintedonacid-freepaperresponsiblymanufacturedfromsustainableforestryinwhichat leasttwotreesareplantedforeachoneusedforpaperproduction. //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–5–[1–8/8]29.3.20053:23PM Contents List of Contributors vii 1 ComputationalFluid Dynamicsmodelling for environmental hydraulics 1 P.D. Bates, S.N. Lane andR.I.Ferguson PART ONE AN OVERVIEW OF COMPUTATIONAL FLUID DYNAMICSSCHEMES 17 2 Fundamental equations for CFD in river flow simulations 19 D.B. Ingham and L. Ma 3 Modellingsolutetransport processesin free surfaceflow CFD schemes 51 I.Guymer, C.A.M.E. Wilson and J.B. Boxall 4 Basic equations for sedimenttransport inCFD for fluvial morphodynamics 71 E.Mosselman 5 Introduction tostatistical turbulence modelling for hydraulic engineering flows 91 F.Sotiropoulos 6 Modellingwetting anddrying processesin hydraulic models 121 P.D. Bates andM.S. Horritt 7 Introduction tonumerical methodsfor fluidflow 147 N.G. Wright 8 Aframework for model verification andvalidation of CFD schemesin naturalopen channel flows 169 S.N. Lane, R.J. Hardy, R.I. Ferguson and D.R. Parsons //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–6–[1–8/8]29.3.20053:23PM vi Contents 9 Parameterisation, validation and uncertainty analysis ofCFD modelsof fluvial and flood hydraulics in thenaturalenvironment 193 M.S. Horritt PART TWO APPLICATIONPOTENTIAL FOR FLUVIAL STUDIES 215 10 Modellingreach-scale fluvial flows 217 S.N. Lane and R.I. Ferguson 11 Numerical modellingof floodplainflow 271 P.D. Bates, M.S. Horritt, N.M. Hunter, D. Mason and D. Cobby 12 Modellingwater qualityprocessesin estuaries 305 R.A. Falconer,B. Lin and S.M. Kashefipour 13 Roughness parameterization inCFD modelling of gravel-bed rivers 329 A.P.Nicholas 14 Modellingof sanddeposition in archaeologicallysignificant reaches ofthe Colorado River inGrandCanyon,USA 357 S. Wiele andM.Torizzo 15 Modellingof open channel flow through vegetation 395 C.A.M.E. Wilson, T.Stoesser and P.D. Bates 16 Ecohydraulics:A new interdisciplinaryfrontier for CFD 429 M.Leclerc 17 Towardsrisk-based predictionin real-world applications of complex hydraulicmodels 461 B.G.Hankinand K.J. Beven 18 CFD for environmental design and management 487 G. Pender, H.P. Morvan, N.G. Wright and D.A. Ervine Author index 511 Subject index 519 //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–7–[1–8/8]29.3.20053:23PM List of Contributors Paul D. Bates Schoolof Geographical Sciences,University ofBristol, UK K.J. Beven IENS, Lancaster University, UK Joby Boxall Department of Civil and Structural Engineering, University of Sheffield, UK David Cobby Environmental SystemsScience Centre, Universityof Reading,UK D.A. Ervine Department ofCivil Engineering,University of Glasgow,UK R.A. Falconer Environmental Water Management Research Centre, Cardiff Schoolof Engineering, Cardiff University, UK RobertI.Ferguson Department ofGeography, University of Durham,UK Ian Guymer Department of Civil and Structural Engineering, University of Sheffield, UK B.G. Hankin Hydro-Logic Ltd, UK R.J. Hardy Departmentof Geography, University of Durham,UK M.S. Horritt School ofGeographicalSciences,University of Bristol, UK Neil M.Hunter Schoolof Geographical Sciences,University ofBristol, UK D.B. Ingham Department of Applied Mathematics, University ofLeeds,UK S.M. Kashefipour Cardiff Schoolof Engineering, Cardiff University, UK Stuart N. Lane Department of Geography, University ofDurham, UK Michel Leclerc Institut National de la Recherche´ Scientifique – Eau, Terre et Environnement,Canada //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/PRELIMS.3D–8–[1–8/8]29.3.20053:23PM viii ListofContributors B. Lin Environmental Water Management Research Centre, Cardiff School of Engineering, Cardiff University, UK L. Ma Energyand Resource Research Institute,University ofLeeds,UK David Mason EnvironmentalSystems Science Centre, University of Reading,UK H.P. Morvan Schoolof Civil Engineering, The University ofNottingham,UK Erik Mosselman WL/Delft Hydraulics, The Netherlands A.P. Nicholas Department of Geography,University ofExeter, UK D.R. Parsons School ofEarthSciences, Universityof Leeds,UK G.Pender DepartmentofCivil&OffshoreEngineering,Heriot-WattUniversity,UK F.Sotiropoulos SchoolofCivil andEnvironmentalEngineering,GeorgiaInstitute of Technology, USA T. Stoesser Institute for Hydromechanics,University of Karlsruhe, Germany MargaretTorizzo Water Resources Division,US Geological Survey, USA Stephen Wiele Water Resources Division,US Geological Survey, USA Catherine Wilson Division of Civil Engineering, Cardiff School of Engineering, CardiffUniversity, UK Nigel G. Wright School ofEngineering,The University of Nottingham, UK //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/C01.3D–1–[1–16/16]28.3.20055:00PM 1 Computational Fluid Dynamics modelling for environmental hydraulics P.D. Bates, S.N. Lane and R.I. Ferguson 1.1 Introduction Computational Fluid Dynamics (CFD) was developed over 40 years ago by engineers and mathematicians to solve heat and mass transfer problems in aeronautics, vehicle aerodynamics, chemical engineering, nuclear design and safety, ventilation andindustrialdesign.Whilstthefundamentalequationsoffluidmotionthatformed thebasisofsuchcodeshadbeenwellknownsincethe19thcentury,theirsolutionfor problems with complex geometry and boundary conditions required the develop- mentofefficientnumericalsolutiontechniquesandtheabilitytoimplementtheseon digitalcomputers.Thedevelopmentofthistechnologyinthe1950sand1960smade suchresearchpossible,andCFDwasoneofthefirstareastotakeadvantageofthe newlyemergentfieldofscientificcomputing.Intheprocess,itwassoonrealizedthat CFDcouldbeanalternativetophysicalmodellinginmanyareasoffluiddynamics, with its advantages oflowercostand greaterflexibility. Computational fluid dynamics is therefore an area of science made possible by, and intrinsically linked to, computing. Its development has paralleled that of com- puterpowerandavailability,andaswemoveintoanageofcheap,powerfuldesktop computing it is now possible, with a little knowledge, to run large and complex 3D simulations on an average personal computer. However, most research advances in CFDcontinuetooriginateintheaeronauticsandindustrialdesigncommunitiesasa Computational Fluid Dynamics: Applications in Environmental Hydraulics. Edited by P.D. Bates, S.N. Lane and R.I. Ferguson Copyright  2005 John Wiley & Sons, Ltd. ISBN: 0-470-84359-4 (HB) //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/C01.3D–2–[1–16/16]28.3.20055:00PM 2 ComputationalFluidDynamics result of the significant investment levels available in these areas. In such applications the boundary conditions, problem geometry and material properties of any solidsurfaces(e.g.dragcoefficients)aretypicallyknownverypreciselyandthecode is applied to a closed system. In such cases it may be possible to characterize the complete set of process mechanisms that exist and also obtain good experimental data for model validation. Major research questions, therefore, concern improvements to the quality of the numerical solution, the scales of flow resolved by the model for fixed computational costs and the representation of sub-grid-scale processes such as turbulence. Considerable effort is expended on topics such as numerical analysis, turbulence modelling, grid generation and adaptive meshing. Tolerance of solution errors is also low, and such codes are predominantly used in a deterministic fashion as alternatives to laboratory experimentation. This reduc- tionist epistemology serves industrial engineering applications well, and the tech- niquesthusdevelopedhaveconsiderablespin-offbenefitinotherdisciplinessuchas environmental hydraulics. EarlyoninthedevelopmentofCFDitwasrealizedthatthetechniquecouldalso be applied to environmental problems to simulate heat and mass transfer in rivers, lakes,oceans,atmospheresandporousmediasuchassoilandrock(e.g.Freezeand Harlan, 1969; King and Norton, 1978; Fischer etal., 1979). The potential for using computermodelstosimulateenvironmentalflowswasobvious;however,theseearly applicationsadoptedthesamedeterministicmethodologyusedinindustrialapplica- tionswhichoftenprovedinappropriate,giventhedatathenavailable.Inreality,the application of CFD to environmental flows leads to a series of problems not encounteredinindustrialapplications:geometryandboundaryconditionsarerarely known with any precision; drag coefficients vary in time and space as result of complex interactions between the material properties of the surface and the flow itself; the driving forces are highly variable, often at scales smaller than the model grid; and the geometry of the problem rarely approximates to a simple, easily meshable surface. Moreover, environmental systems are open and should be conceivedascomplexassemblagesofmanydifferentprocessesandinputs,notallof whichwillbewellcharacterizedinanygivenapplication.Modelvalidationdatamay notbeavailablewhichtestsallrelevantaspectsofmodelperformancetoasufficient level of detail. In fact, given that CFD models adopt finite representations of time and space that may be very different to the time and space scales over which observations are obtained, it may actually be very difficult to measure those quan- tities predicted by a given code. In contrast to industrial applications of CFD, environmental applications are characterized by considerable uncertainty over almost every aspect of the modelling process and it may therefore become very difficulttodiagnosewhyamodelisgoingwrong.Forexample,amismatchbetween a model and available validation data may be the result of a poor choice of conceptual model given the problem in hand, lack of data to characterize the problem geometry and boundary conditions, an incorrect parameterization or just insufficientorinappropriatevalidationdata.Mostlikelyallthesefactorswillapply! Whilst this does not mean that CFD models cannot be used to perform numerical experiments in environmental hydraulics, it does suggest that care is required in interpreting model studies which purport to mimic real flow events and which include comparisons withreal data. //INTEGRAS/KCG/PAGINATION/WILEY/CPT/FINALS_28-03-05/C01.3D–3–[1–16/16]28.3.20055:00PM CFDmodellingforenvironmentalhydraulics 3 Environmental applications of CFD thus have some fundamentally different characteristics from other applications of this technology, and as a consequence suchapplicationsmayhaveverydifferentresearchpriorities. Thisisnottosaythat environmental CFD modellers should be unconcerned about the numerical tech- niquestheyuseoraboutthequalityofthenumericalsolutionstheyproduce.Neither does it imply that more highly resolved model grids and greater levels of process inclusion will not lead to more physically realistic models (even if the utility of this reductionistapproachmaybedifficulttoproveinourcase).Rather,itsuggeststhat thegreatestuncertaintiesinenvironmentalCFDmodellinglieelsewhere,andthatthe key research challenges relate to the identification, quantification and reduction of these. This new research agenda focuses on such questions as: coupling CFD with complexnaturalterrain;extendingprocessrepresentationtoconsiderationofcoupled sediment-flow, water quality-flow and biotic–abiotic problems; scale and resolution effects,includingupscaling;issuesoverwhatmakessufficientprocessrepresentationin terms of model simplification; model validation; complex sensitivity and uncertainty analysis; and possible model equifinality. Uncertainty is a particular challenge as uncertaintiesmaybecompensating,interactingandnon-linear.Further,thedatasets availabletounderstandthemmaybesparseandcontainsignificantbutpoorlyknown errors that vary strongly in time and space. The result is that there may be many combinationsofmodelsandparametersthatfittheavailabledataequallywell. In proposing solutions to these problems, environmental CFD modellers have a distinctivecontributiontomaketotheoveralldisciplineandthereisthepotentialto contribute significant innovative science that may find application in many fields. Whilst much research in ‘mainstream’ CFD requires very high level mathematical ability that is typically the preserve of a select group of specialists, solution to the problems outlined above requires a different skill set for which environmental scientists may be well suited. The ability to deal with problems characterized by sparse and uncertain data where there may even be debate over the fundamental process mechanisms at work is a key part of scientific training in environmental engineeringandthegeosciences.Hence,inenvironmentalapplicationsofCFDthere are scientific problems of model development and analysis that are not well antici- pated or solved by standard CFD research and to which civil engineers, environ- mentalscientists and geographers can contributesignificant insight. Application of CFD techniques to real-world environmental problems has increased sharply in the last decade due to an improving ability to deal with the uncertainties noted above. In part this has been due to improvements in computer powerandstorage,whichhaveallowedflowsovercomplexnaturaltopographiesto be simulated for the first time, and to wider availability of user-friendly code. However, this alone does not explain the rise of environmental applications of CFD. A further major factor is the increased availability of the necessary digital datasetstosetupandtotestsuchmodels.Instrumentationdevelopmentinavariety offieldshasyieldednewtechnologiesfortopographicsurveying(includingairborne laser altimetry, stereo-photogrammetry and the Global Positioning System), bathy- metricsurvey(includingsidescansonarandwideswathsonar)andvelocitymeasure- ment (including acoustic Doppler current profilers and large-scale particle image velocimetry). Such instruments yield data that are critical for environmental applications of CFD and allow users to at least begin the process of uncertainty