Tapan K. Sengupta · Swagata Bhaumik DNS of Wall- Bounded Turbulent Flows A First Principle Approach DNS of Wall-Bounded Turbulent Flows Tapan K. Sengupta Swagata Bhaumik (cid:129) DNS of Wall-Bounded Turbulent Flows A First Principle Approach 123 Tapan K.Sengupta Swagata Bhaumik Department ofAerospace Engineering Department ofMechanical Engineering Indian Institute of Technology Kanpur Indian Institute of Technology Jammu Kanpur,Uttar Pradesh Jammu,Jammu &Kashmir India India ISBN978-981-13-0037-0 ISBN978-981-13-0038-7 (eBook) https://doi.org/10.1007/978-981-13-0038-7 LibraryofCongressControlNumber:2018940403 ©SpringerNatureSingaporePteLtd.2019 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. 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Printedonacid-freepaper ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSingaporePteLtd. partofSpringerNature Theregisteredcompanyaddressis:152BeachRoad,#21-01/04GatewayEast,Singapore189721, Singapore Preface A long habit of not thinking a thing is wrong gives it a superficial appearance of being right. Reason obeys itself, andignorancesubmitstowhateverisdictatedtoit. TomPaine There are many books and monographs on instability and transition, including onebyoneoftheauthorsofthismonograph.Despitethesebooks,thismonograph is written with a specific purpose of presenting a detailed account of what consti- tutes direct numerical simulation (DNS) of flow from receptivity stage to fully developed turbulent flow over flat plate, while simulating the classical transition experimentsforzeropressuregradientboundarylayer.Thishasbeenmadepossible with the work of the authors’ colleagues and students, proposing new theoretical andcomputationalresults,whichestablishadeterministicroutetoturbulence,asin the classical experimental efforts [3, 5, 7]. TheNavier–StokesequationgovernsfluidflowsandReynoldsexplainedthatthe exact solution of the Navier–Stokes equation, even when it exists, is unable to maintainitsstabilitywithrespecttoomnipresentsmalldisturbancesintheflow.An equilibrium solution ensures satisfaction of conservation principles of mass, momentum,andenergybalance,yettheflowinthefamouspipeflowexperimentof Reynolds disintegrated into sinuous motion, eventually leading to turbulent flow. Thisonsethasbeenattributedtotheinstabilityofflowseversince.However,even today the transition to turbulence in pipe flow is not completely understood. Another canonical problem which attracted the attention of researchers in the beginning is the flow over a flat plate. In studying instability of this flow field, Rayleigh developed his stability equation, but it was not amenable to study con- vective disturbances, which is the signature of transition for zero pressure gradient boundarylayerflow.Bythebeginningoftwentiethcentury,itbecameevidentthat the instability problem is intractable without the inclusion of the effects of second derivative of velocity profile and viscous actions. These latter effects have been termedasresistiveinstability,whichisincontradictiontotheassumptionmadeby v vi Preface earlypioneers,whomistakenlyconsideredtheactionofviscousforcestoattenuate disturbances and was considered not central to the study of instability. ThiswasthereasonforOrrandSommerfeldtoindependentlycomeupwiththe famous Orr–Sommerfeld equation, which was investigated by Tietjens [14] and Heisenberg [4]. However, it was the definitive attempt by Tollmien that paved the understanding the concept of critical Reynolds number [15]. Following this lead, Schlichting also studied the instability of zero pressure gradient boundary layer, while making some implicit assumption which connected the temporal and spatial growthofdisturbances,whichhassincebeenaddressedbyinvokingtheconceptof group velocity [8]. One of the central themes of Tollmien and Schlichting’s work was to show the presence of growing waves in limited part of the flow, and this is now called the Tollmien–Schlichting (TS) waves. This eigenvalue analysis is performed by neglecting the growth of boundary layer. We would like to mention thatstudyingflowinstabilitybytemporalandspatialtheoryandartificiallypatching thetwotogetherisfraughtwithdanger.Thishasbeendemonstratedbytheauthors and colleagues that there is really no need to make this artificial demarcation into spatialandtemporalroutes.Thebestcourseofactionistoadoptthespatio-temporal route to avoid this ambiguity. While studying instability of mixed convection boundary layer, authors came across a perplexing situation, when a singularly cooledplatedemonstratedsimultaneouspresenceoftemporalandspatialinstability [10].TheproblemwasresolvedbecauseoftheavailabilityofDNSresultsobtained by high-accuracy method, which showed the flow to follow primarily temporal growth, and not the spatial route (the growth should be strictly stated to be via spatio-temporal route). This emphasizes the need to perform spatio-temporal analysis, which has been practiced and yielded new insights, which form the contents of this treatise. However, despite Taylor demonstrating the strength of linear stability of flow insideconcentriccylinder[12],TSwavecouldnotbedetectedexperimentally.This created doubts about the existence of TS wave and, in turn, on the relevance of viscous linear theory. This problem was resolved by Dryden’s group, by demon- strating for the first time the existence ofTS wave by vibrating a ribbon inside the boundarylayer,withtheresultsannouncedaftertheSecondWorldWar[3,5].This experimentalapproachmaybetermedasfrequencyresponseofthefluiddynamical system.Itwouldbeappropriatetonotethatexcitingtheflowatanyfrequencywill notleadtoflowinstability,asthevibratingdiaphragmexperimentofTaylor[13]at 2 Hz demonstrated. The frequencies to be excited were present in the works of Tollmien and Schlichting [8, 15], but Taylor’s experimental vibration was at too low a frequency [13]. This aspect of how to experimentally study eigenvalue problemisnotclearlyunderstood.Inarecentwork,researchershaveexplainedthe relationship between frequency response and instability for an associated problem of bifurcation [6]. Viewing fluid flows as dynamical systems, it is thus unwise to ignore the receptivity aspect. Receptivity was emphasized by Schubauer and Skramstad in reporting their classic experimental results [7]. Thereafter, reported TS waves as Preface vii earlymarkerofflowinstabilitywasreadilyembracedbytheresearchcommunityto conclude prematurely that TS waves are the cause for flow transition. It is worth- while remembering that vortical excitation validated instability theory, while the acoustic excitation did not! Also, instability theory does not require any specific excitation,exceptinprescribingthequalitativenatureofboundaryconditions.The main feature of this monograph is to relate receptivity with flow instability and show how different routes of excitation lead to different types of disturbance evolution. This has been achieved here primarily by DNS to explain theoretical aspects of the flow. Viscous instability results also suffered credibility due to the use of a parallel flow assumption for the equilibrium flow, along with linearization. This criticism waspartlysilencedbyexperimentalverificationprovided[7],butwhetherTSwaves cancausetransitionornotwasnotknownforalongtime,tillthedefinitiveroutesof transitionwereidentifiedfor2Dzeropressuregradientflow[9].Ithasbeenshown by the present authors that when the Navier–Stokes equation is computed in 2D framework to mimic the experiment [7] for moderate- to high-frequency wall excitation, created TS wave packet remains passive, while the spatio-temporal wave-front (STWF) causes transition. The STWF is the first wave front that is createduponstartingofftheexcitation,asinanexperiment,whichhastheproperty to regenerate other STWF in its wake [9]. It is interesting to note that STWF was originally proposed in research on electromagnetic wave propagation [2]. In fluid dynamics,themajorsuccessintrackingSTWFfromthespatio-temporaldynamics ofOrr–Sommerfeldequationwasreported[11],followingthedevelopedtechnique of Bromwich contour integral method. While these have been obtained for the frequency response of disturbance evolution, corresponding role of STWF during impulse response has been reported only recently [1], which also shows that the same physical mechanism of STWF explains the features of geophysical phenom- ena like tsunami and rogue waves. This book has evolved into an account of the research interests of the authors over the years. Efforts are made to keep the treatment at an elementary level requiring rudimentary knowledge of calculus, Laplace–Fourier transform, and complexanalysis,whichshouldbeequallyamenabletoundergraduatestudents,as well as serious researchers in the field of hydrodynamics and mixed convection. Thismonographshowstoreadersthatwithoutgoodcomputing,thissubjectwillbe poorer in linking spatio-temporal growth, instability at low frequencies, and the actual physical mechanisms of transition. In providing computational results from receptivitytoafullydevelopedturbulentstageof2Dand3Ddisturbanceflows,we also definitely provide the basis of experimental approach for transition to turbu- lence. In doing so, we state that turbulence is deterministic in its origin, as it is implicitly assumed in transition experiments [3, 5, 7]. Trained with high-accuracy computing methods, users of this monograph will be able to further contribute in this rich field of nonlinear dynamics. Thus, the emphasis of the monograph is on DNS of transitional and turbulent flows,basisofwhicharelaidoutinChap.2.TheapplicationsofDNStechniqueare usedtoexplainreceptivityandinstabilityinhydrodynamics andmixedconvection viii Preface flows in Chap. 3. The power of DNS is demonstrated by using results to explain vortex-induced instability in a nonlinear framework to explain receptivity and instability in Chap. 4. This is done by developed disturbance enstrophy transport equation [16, 17]. This provides a nonlinear framework based on Navier–Stokes equation without making any assumption on the equilibrium flow. Another non- linear framework to study instability in this chapter is by using enstrophy-based proper orthogonal decomposition. The last two chapters are to demonstrate the powerandaccuracypresentedbytheDNStechniques described inearlierchapters toshowthatSTWFistheprecursorsoftransitiontoturbulence,forboth2Dand3D disturbanceflowsimulations.Theresultingturbulentflowsareashavebeencreated experimentally[3,5,7].Thetransitiontoturbulenceisshowntobeexperimentally obtained for the integral properties and presented in textbooks. In closing this discussion, we note that the subject has matured very rapidly in recent times with the advent of very high-accuracy methods of computing, which will lead to an explosive growth of activities in the subject field. The contents of the monograph canbeadoptedastextforahigh-levelcourseonDNSandtransitiontoturbulence. The contents of this monograph are based on the doctoral thesis work of one of the authors and the other graduate students who have been associated with the firstauthoroverthelastthreedecades.Thecontentshavebeenspecificallyenriched by faculty colleagues in NUS, Singapore, specifically by Profs. Y. T. Chew, T.T.Lim,B.C.Khoo,K.S.Yeo,andS.ChangandProf.PierreSagaut(UPMC), Prof. Julio Soria (Monash University), Prof. W. Schneider (TUW, Vienna), Prof. K. R. Sreenivasan (ICTP and NYU), Prof. M. Klocker (University of Stuttgart), Dr.J.M.Kendall(JetPropulsionLab,USA),Dr.B.R.Noack(Pprime,University of Poitier, France), Prof. M. Deville and Prof. F. Gallaire (EPFL, Switzerland), Prof.S.Girimaji(TAMU,USA),Prof.P.J.Strykowski(UniversityofMinnesota), and Prof. A. Tumin (University of Arizona). Much of our work on receptivity has been influenced by the works of Prof. H. Fasel (University of Arizona). The first author acknowledges the influence of Prof. M. Gaster and Prof. D. G. Crighton (University of Cambridge) for encouraging him to develop a theory of receptivity. Manyofthecontributorsofthisbookarenowfacultycolleaguesindifferent parts. It is our pleasant duty to acknowledge the contributions by Sandeep Nijhawan, Manish Ballav, A. P. Sinha, Vivek Rana, Manoj T. Nair, K. Venkatasubbaiah, A. K. Rao, Manojit Chattopadhyay, Z. Y. Wang, A. Dipankar, S. Sarkar, S. De, Yogesh Bhumkar, Vijay Vedula, Manoj Rajpoot, S. Unnikrishnan, R. Bose, N.A.Sreejith,AshishBhole,andSoumyoSengupta.Inaveryrecentdevelopment, the authors have been looking at “exact” nonlinear theories of instability for incompressible flows, based on disturbance mechanical energy and disturbance enstrophy, with the former covered in the text here. However, we refrain from providingthedetailsonthetheorybasedondisturbanceenstrophyandiscurrently being probed for different types offlow fields and would be described elsewhere. The authors acknowledge Aditi Sengupta and V. K. Suman for helping with the development of this instability theory based on disturbance enstrophy [17]. Preface ix Theauthorswouldliketoacknowledgethecompetenthelpprovidedintypingthis materialbyMrs.BabyGaurandMrs.ShashiShukla.Specifically,Mrs.Gaurtakes exceptional care in typing the text and preparing figures at all times. We also acknowledge various helps provided to us by Mr. Mukesh Kumar. Kanpur, India Tapan K. Sengupta Jammu & Kashmir, India Swagata Bhaumik References 1. Bhaumik,S.,&Sengupta,T.K.(2017).Impulseresponseandspatio-temporalwave-packets: Thecommonfeatureofroguewaves,tsunamiandtransitiontoturbulence.PhysicsofFluids, 29,124103. 2. Brillouin,L.(1960).Wavepropagationandgroupvelocity.NewYork:AcademicPress. 3. Dryden, H. L. (1955). Fifty years of boundary-layer theory and experiment. Science, 121 (3142),375–380. 4. Heisenberg, W.(1924).Üeberstabilitätundturbulenz von flüssigkeitsströmen.Annalender Physik,74,577–627. 5. Klebanoff,P.S.,Tidstrom,K.D.,&Sargent,L.M.(1962).Thethree-dimensionalnatureof boundary-layerinstability.JournalofFluidMechanics,12,1–34. 6. Lestandi,L.,Bhaumik,S.,Avatar,G.R.K.C.,Mejdi,A.,&Sengupta,T.K.(2018).Multiple Hopf bifurcations and flow dynamics inside a 2D singular lid driven cavity. Computers & Fluids. 7. Schubauer, G. B.,& Skramstad, H. K.(1947). Laminar boundarylayer oscillations andthe stabilityoflaminarflow.JournaloftheAeronauticalSciences,14(2),69–78. 8. Schlichting, H. (1933). Zur entstehung der turbulenz bei der plattenströmung. Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, 181–208. 9. Sengupta,T.K.,&Bhaumik,S.(2011).Onsetofturbulencefromthereceptivitystageoffluid flows.PhysicalReviewLetters,107(15),154501. 10. Sengupta,T.K.,Bhaumik,S.,&Bose,R.(2013).Directnumericalsimulationoftransitional mixedconvectionflows:Viscousandinviscidinstabilitymechanisms.PhysicsofFluids,25, 094102. 11. Sengupta,T.K.,Rao,A.K.,&Venkatasubbaiah,K.(2006).Spatio–temporalgrowingwave frontsinspatiallystableboundarylayers.PhysicalReviewLetters,96(22),224504. 12. Taylor, G. I.(1923). Stability of aviscous liquid contained between tworotating cylinders. PhilosophicalTransactionsoftheRoyalSociety(London),A223,289–343. 13. Taylor,G.I.(1939).Somerecentdevelopmentsinthestudyofturbulence.InJ.P.DenHartog &H.Peters(Eds.),ProceedingsoftheVthInternationalConferenceonAppliedMechanics. 14. Tietjens,O.(1925).Beiträgezurenstehungderturbulenz.ZAMM,5,200–217. 15. Tollmien,W.(1931).Überdieenstehungderturbulenz.I,Englishtranslation.NACATM609. 16. Sengupta, T. K., Sharma, N. & Sengupta, A. (2018). Non-linear instability analysis of the two-dimensional Navier-Stokes equation: The Taylor-Green vortex problem. Physics of Fluids(Accepted). 17. Sengupta, A., Suman, V. K., Sengupta, T. K. & Bhaumik, S. (2018). An enstrophy-based linearandnon-linearreceptivitytheory.PhysicsofFluids(Accepted). Contents 1 DNS of Wall-Bounded Turbulent Flow: An Introduction. . . . . . . . . 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Why Deterministic Study Is More Relevant than Stochastic Approaches?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2.1 Historic Developments . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Present State of Art in the Field . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Different Transition Routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.5 Role of Equilibrium Flow in DNS. . . . . . . . . . . . . . . . . . . . . . . . 6 1.6 What Is Instability? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.7 Temporal and Spatial Instability . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.8 Some Instability Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.8.1 Kelvin–Helmholtz Instability . . . . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2 DNS of Navier–Stokes Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.1 Fluid Dynamical Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.1.1 Equation of Continuity. . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2 Momentum Conservation Equation . . . . . . . . . . . . . . . . . 19 2.1.3 Energy Conservation Equation . . . . . . . . . . . . . . . . . . . . 22 2.1.4 Alternate Forms of the Energy Equation . . . . . . . . . . . . . 23 2.1.5 Vorticity Transport Equation for Incompressible Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.6 Derived Variable Formulation for 2D Incompressible Navier–Stokes Equation . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2 Spatial and Temporal Scales for Transitional and Turbulent Flows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3 Numerical Methods for Developing DNS/LES . . . . . . . . . . . . . . . 31 2.3.1 Waves – Building Blocks of a Disturbance Field. . . . . . . 31 2.3.2 Resolution of Spatial Discretization. . . . . . . . . . . . . . . . . 34 2.3.3 High-Accuracy Compact Schemes for Evaluation of First Derivatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 xi